Plaintext
Linux Storage
Paul Cobbaut
Linux Storage
Paul Cobbaut
Paul Cobbaut
Publication date 2015-05-24 CEST
Abstract
This book is meant to be used in an instructor-led training. For self-study, the intent is to read
this book next to a working Linux computer so you can immediately do every subject, practicing
each command.
This book is aimed at novice Linux system administrators (and might be interesting and useful
for home users that want to know a bit more about their Linux system). However, this book
is not meant as an introduction to Linux desktop applications like text editors, browsers, mail
clients, multimedia or office applications.
More information and free .pdf available at http://linux-training.be .
Feel free to contact the author:
• Paul Cobbaut: paul.cobbaut@gmail.com, http://www.linkedin.com/in/cobbaut
Contributors to the Linux Training project are:
• Serge van Ginderachter: serge@ginsys.be, build scripts; infrastructure setup; minor stuff
• Hendrik De Vloed: hendrik.devloed@ugent.be, buildheader.pl script
We'd also like to thank our reviewers:
• Wouter Verhelst: wouter@grep.be, http://grep.be
• Geert Goossens: mail.goossens.geert@gmail.com, http://www.linkedin.com/in/
geertgoossens
• Elie De Brauwer: elie@de-brauwer.be, http://www.de-brauwer.be
• Christophe Vandeplas: christophe@vandeplas.com, http://christophe.vandeplas.com
• Bert Desmet: bert@devnox.be, http://bdesmet.be
• Rich Yonts: richyonts@gmail.com,
Copyright 2007-2015 Paul Cobbaut
Permission is granted to copy, distribute and/or modify this document under the terms of the
GNU Free Documentation License, Version 1.3 or any later version published by the Free
Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
Texts. A copy of the license is included in the section entitled 'GNU Free Documentation
License'.
Table of Contents
I. file security ................................................................................................................................................... 1
1. standard file permissions ................................................................................................................ 3
1.1. file ownership ........................................................................................................................ 4
1.2. list of special files ................................................................................................................. 6
1.3. permissions ............................................................................................................................ 7
1.4. practice: standard file permissions ...................................................................................... 12
1.5. solution: standard file permissions ...................................................................................... 13
2. advanced file permissions .............................................................................................................. 15
2.1. sticky bit on directory ......................................................................................................... 16
2.2. setgid bit on directory ......................................................................................................... 16
2.3. setgid and setuid on regular files ........................................................................................ 17
2.4. setuid on sudo ..................................................................................................................... 17
2.5. practice: sticky, setuid and setgid bits ................................................................................ 18
2.6. solution: sticky, setuid and setgid bits ................................................................................ 19
3. access control lists .......................................................................................................................... 21
3.1. acl in /etc/fstab ..................................................................................................................... 22
3.2. getfacl .................................................................................................................................. 22
3.3. setfacl ................................................................................................................................... 22
3.4. remove an acl entry ............................................................................................................. 23
3.5. remove the complete acl ..................................................................................................... 23
3.6. the acl mask ......................................................................................................................... 23
3.7. eiciel ..................................................................................................................................... 24
4. file links ........................................................................................................................................... 25
4.1. inodes ................................................................................................................................... 26
4.2. about directories .................................................................................................................. 27
4.3. hard links ............................................................................................................................. 28
4.4. symbolic links ...................................................................................................................... 29
4.5. removing links ..................................................................................................................... 29
4.6. practice : links ..................................................................................................................... 30
4.7. solution : links ..................................................................................................................... 31
II. disk management ...................................................................................................................................... 32
5. disk devices ..................................................................................................................................... 35
5.1. terminology .......................................................................................................................... 36
5.2. device naming ...................................................................................................................... 38
5.3. discovering disk devices ..................................................................................................... 39
5.4. erasing a hard disk .............................................................................................................. 44
5.5. advanced hard disk settings ................................................................................................ 45
5.6. practice: hard disk devices .................................................................................................. 46
5.7. solution: hard disk devices .................................................................................................. 47
6. disk partitions ................................................................................................................................. 49
6.1. about partitions .................................................................................................................... 50
6.2. discovering partitions .......................................................................................................... 51
6.3. partitioning new disks ......................................................................................................... 53
6.4. about the partition table ...................................................................................................... 55
6.5. GUID partition table ........................................................................................................... 56
6.6. labeling with parted ............................................................................................................. 56
6.7. practice: partitions ............................................................................................................... 58
6.8. solution: partitions ............................................................................................................... 59
7. file systems ...................................................................................................................................... 60
7.1. about file systems ................................................................................................................ 61
7.2. common file systems ........................................................................................................... 62
7.3. putting a file system on a partition ..................................................................................... 65
7.4. tuning a file system ............................................................................................................. 66
7.5. checking a file system ......................................................................................................... 67
7.6. practice: file systems ........................................................................................................... 68
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Linux Storage
7.7. solution: file systems ........................................................................................................... 69
8. mounting .......................................................................................................................................... 70
8.1. mounting local file systems ................................................................................................ 71
8.2. displaying mounted file systems ......................................................................................... 72
8.3. from start to finish .............................................................................................................. 74
8.4. permanent mounts ............................................................................................................... 75
8.5. securing mounts ................................................................................................................... 76
8.6. mounting remote file systems ............................................................................................. 77
8.7. practice: mounting file systems .......................................................................................... 78
8.8. solution: mounting file systems .......................................................................................... 79
9. troubleshooting tools ...................................................................................................................... 81
9.1. lsof ....................................................................................................................................... 82
9.2. fuser ..................................................................................................................................... 83
9.3. chroot ................................................................................................................................... 84
9.4. iostat ..................................................................................................................................... 85
9.5. iotop ..................................................................................................................................... 86
9.6. vmstat ................................................................................................................................... 87
9.7. practice: troubleshooting tools ............................................................................................ 88
9.8. solution: troubleshooting tools ............................................................................................ 89
10. introduction to uuid's .................................................................................................................. 90
10.1. about unique objects .......................................................................................................... 91
10.2. tune2fs ................................................................................................................................ 91
10.3. uuid .................................................................................................................................... 91
10.4. uuid in /etc/fstab ................................................................................................................ 92
10.5. uuid as a boot device ........................................................................................................ 93
10.6. practice: uuid and filesystems ........................................................................................... 94
10.7. solution: uuid and filesystems ........................................................................................... 95
11. introduction to raid ...................................................................................................................... 96
11.1. hardware or software ......................................................................................................... 96
11.2. raid levels .......................................................................................................................... 97
11.3. building a software raid5 array ......................................................................................... 99
11.4. practice: raid .................................................................................................................... 102
11.5. solution: raid .................................................................................................................... 103
12. logical volume management ...................................................................................................... 104
12.1. introduction to lvm .......................................................................................................... 105
12.2. lvm terminology .............................................................................................................. 106
12.3. example: using lvm ......................................................................................................... 107
12.4. example: extend a logical volume .................................................................................. 109
12.5. example: resize a physical Volume ................................................................................ 111
12.6. example: mirror a logical volume ................................................................................... 113
12.7. example: snapshot a logical volume ............................................................................... 114
12.8. verifying existing physical volumes ................................................................................ 115
12.9. verifying existing volume groups ................................................................................... 117
12.10. verifying existing logical volumes ................................................................................ 118
12.11. manage physical volumes .............................................................................................. 119
12.12. manage volume groups ................................................................................................. 121
12.13. manage logical volumes ................................................................................................ 123
12.14. practice : lvm ................................................................................................................. 125
12.15. solution : lvm ................................................................................................................. 126
13. iSCSI devices .............................................................................................................................. 130
13.1. iSCSI terminology ........................................................................................................... 131
13.2. iSCSI Target in RHEL/CentOS ...................................................................................... 131
13.3. iSCSI Initiator in RHEL/CentOS .................................................................................... 133
13.4. iSCSI target on Debian ................................................................................................... 135
13.5. iSCSI target setup with dd files ...................................................................................... 136
13.6. ISCSI initiator on ubuntu ................................................................................................ 138
13.7. using iSCSI devices ......................................................................................................... 140
13.8. iSCSI Target RHEL7/CentOS7 ....................................................................................... 141
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Linux Storage
13.9. iSCSI Initiator RHEL7/CentOS7 .................................................................................... 143
13.10. practice: iSCSI devices ................................................................................................. 145
13.11. solution: iSCSI devices ................................................................................................. 146
14. introduction to multipathing ..................................................................................................... 150
14.1. install multipath ............................................................................................................... 151
14.2. configure multipath ......................................................................................................... 151
14.3. network ............................................................................................................................ 152
14.4. start multipathd and iscsi ................................................................................................ 152
14.5. multipath list .................................................................................................................... 154
14.6. using the device ............................................................................................................... 155
14.7. practice: multipathing ...................................................................................................... 156
14.8. solution: multipathing ...................................................................................................... 157
III. backup management .............................................................................................................................. 159
15. backup ......................................................................................................................................... 161
15.1. About tape devices .......................................................................................................... 161
15.2. Compression .................................................................................................................... 162
15.3. tar ..................................................................................................................................... 162
15.4. Backup Types .................................................................................................................. 164
15.5. dump and restore ............................................................................................................. 165
15.6. cpio .................................................................................................................................. 165
15.7. dd ..................................................................................................................................... 166
15.8. split .................................................................................................................................. 167
15.9. practice: backup ............................................................................................................... 167
IV. mysql database ...................................................................................................................................... 169
16. introduction to sql using mysql ................................................................................................ 171
16.1. installing mysql ............................................................................................................... 172
16.2. accessing mysql ............................................................................................................... 173
16.3. mysql databases ............................................................................................................... 175
16.4. mysql tables ..................................................................................................................... 177
16.5. mysql records .................................................................................................................. 179
16.6. joining two tables ............................................................................................................ 182
16.7. mysql triggers .................................................................................................................. 183
V. Introduction to Samba ............................................................................................................................ 185
17. introduction to samba ................................................................................................................ 188
17.1. verify installed version .................................................................................................... 189
17.2. installing samba ............................................................................................................... 190
17.3. documentation .................................................................................................................. 191
17.4. starting and stopping samba ............................................................................................ 192
17.5. samba daemons ................................................................................................................ 193
17.6. the SMB protocol ............................................................................................................ 194
17.7. practice: introduction to samba ....................................................................................... 195
18. getting started with samba ........................................................................................................ 196
18.1. /etc/samba/smb.conf ......................................................................................................... 197
18.2. /usr/bin/testparm ............................................................................................................... 198
18.3. /usr/bin/smbclient ............................................................................................................. 199
18.4. /usr/bin/smbtree ................................................................................................................ 201
18.5. server string ..................................................................................................................... 202
18.6. Samba Web Administration Tool (SWAT) .................................................................... 203
18.7. practice: getting started with samba ................................................................................ 204
18.8. solution: getting started with samba ............................................................................... 205
19. a read only file server ................................................................................................................ 207
19.1. Setting up a directory to share ........................................................................................ 208
19.2. configure the share .......................................................................................................... 208
19.3. restart the server .............................................................................................................. 209
19.4. verify the share ................................................................................................................ 209
19.5. a note on netcat ............................................................................................................... 211
19.6. practice: read only file server ......................................................................................... 212
19.7. solution: read only file server ......................................................................................... 213
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Linux Storage
20. a writable file server .................................................................................................................. 214
20.1. set up a directory to share ............................................................................................... 215
20.2. share section in smb.conf ................................................................................................ 215
20.3. configure the share .......................................................................................................... 215
20.4. test connection with windows ......................................................................................... 215
20.5. test writing with windows ............................................................................................... 216
20.6. How is this possible ? ..................................................................................................... 216
20.7. practice: writable file server ............................................................................................ 217
20.8. solution: writable file server ........................................................................................... 218
21. samba first user account ........................................................................................................... 219
21.1. creating a samba user ...................................................................................................... 220
21.2. ownership of files ............................................................................................................ 220
21.3. /usr/bin/smbpasswd .......................................................................................................... 220
21.4. /etc/samba/smbpasswd ..................................................................................................... 220
21.5. passdb backend ................................................................................................................ 221
21.6. forcing this user ............................................................................................................... 221
21.7. practice: first samba user account ................................................................................... 222
21.8. solution: first samba user account ................................................................................... 223
22. samba authentication ................................................................................................................. 224
22.1. creating the users on Linux ............................................................................................. 225
22.2. creating the users on samba ............................................................................................ 225
22.3. security = user ................................................................................................................. 225
22.4. configuring the share ....................................................................................................... 226
22.5. testing access with net use .............................................................................................. 226
22.6. testing access with smbclient .......................................................................................... 226
22.7. verify ownership .............................................................................................................. 227
22.8. common problems ........................................................................................................... 227
22.9. practice : samba authentication ....................................................................................... 229
22.10. solution: samba authentication ...................................................................................... 230
23. samba securing shares ............................................................................................................... 231
23.1. security based on user name ........................................................................................... 232
23.2. security based on ip-address ........................................................................................... 232
23.3. security through obscurity ............................................................................................... 233
23.4. file system security .......................................................................................................... 233
23.5. practice: securing shares ................................................................................................. 235
23.6. solution: securing shares ................................................................................................. 236
24. samba domain member ............................................................................................................. 238
24.1. changes in smb.conf ........................................................................................................ 239
24.2. joining an Active Directory domain ............................................................................... 240
24.3. winbind ............................................................................................................................ 241
24.4. wbinfo .............................................................................................................................. 241
24.5. getent ................................................................................................................................ 242
24.6. file ownership .................................................................................................................. 243
24.7. practice : samba domain member .................................................................................... 244
25. samba domain controller ........................................................................................................... 245
25.1. about Domain Controllers ............................................................................................... 246
25.2. About security modes ...................................................................................................... 246
25.3. About password backends ............................................................................................... 247
25.4. [global] section in smb.conf ............................................................................................ 247
25.5. netlogon share .................................................................................................................. 248
25.6. other [share] sections ....................................................................................................... 248
25.7. Users and Groups ............................................................................................................ 249
25.8. tdbsam .............................................................................................................................. 249
25.9. about computer accounts ................................................................................................. 250
25.10. local or roaming profiles ............................................................................................... 250
25.11. Groups in NTFS acls ..................................................................................................... 251
25.12. logon scripts .................................................................................................................. 252
25.13. practice: samba domain controller ................................................................................ 253
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Linux Storage
26. a brief look at samba 4 ............................................................................................................. 254
26.1. Samba 4 alpha 6 .............................................................................................................. 256
VI. Appendix ................................................................................................................................................ 258
A. License .......................................................................................................................................... 260
Index ............................................................................................................................................................. 267
vii
List of Tables
1.1. Unix special files ...................................................................................................................................... 6
1.2. standard Unix file permissions ................................................................................................................. 7
1.3. Unix file permissions position ................................................................................................................. 7
1.4. Octal permissions ................................................................................................................................... 10
5.1. ide device naming .................................................................................................................................. 38
5.2. scsi device naming ................................................................................................................................. 38
6.1. primary, extended and logical partitions ................................................................................................ 50
6.2. Partition naming ..................................................................................................................................... 50
13.1. iSCSI Target and Initiator practice .................................................................................................... 145
13.2. iSCSI Target and Initiator practice .................................................................................................... 147
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Part I. file security
Table of Contents
1. standard file permissions .......................................................................................................................... 3
1.1. file ownership .................................................................................................................................. 4
1.2. list of special files ........................................................................................................................... 6
1.3. permissions ...................................................................................................................................... 7
1.4. practice: standard file permissions ............................................................................................... 12
1.5. solution: standard file permissions ............................................................................................... 13
2. advanced file permissions ....................................................................................................................... 15
2.1. sticky bit on directory ................................................................................................................... 16
2.2. setgid bit on directory ................................................................................................................... 16
2.3. setgid and setuid on regular files ................................................................................................. 17
2.4. setuid on sudo ............................................................................................................................... 17
2.5. practice: sticky, setuid and setgid bits .......................................................................................... 18
2.6. solution: sticky, setuid and setgid bits ......................................................................................... 19
3. access control lists ................................................................................................................................... 21
3.1. acl in /etc/fstab .............................................................................................................................. 22
3.2. getfacl ............................................................................................................................................ 22
3.3. setfacl ............................................................................................................................................. 22
3.4. remove an acl entry ...................................................................................................................... 23
3.5. remove the complete acl ............................................................................................................... 23
3.6. the acl mask .................................................................................................................................. 23
3.7. eiciel .............................................................................................................................................. 24
4. file links ..................................................................................................................................................... 25
4.1. inodes ............................................................................................................................................. 26
4.2. about directories ............................................................................................................................ 27
4.3. hard links ....................................................................................................................................... 28
4.4. symbolic links ............................................................................................................................... 29
4.5. removing links .............................................................................................................................. 29
4.6. practice : links ............................................................................................................................... 30
4.7. solution : links ............................................................................................................................... 31
2
Chapter 1. standard file permissions
This chapter contains details about basic file security through file ownership and file
permissions.
3
standard file permissions
1.1. file ownership
1.1.1. user owner and group owner
The users and groups of a system can be locally managed in /etc/passwd and /etc/group,
or they can be in a NIS, LDAP, or Samba domain. These users and groups can own files.
Actually, every file has a user owner and a group owner, as can be seen in the following
screenshot.
paul@rhel65:~/owners$ ls -lh
total 636K
-rw-r--r--. 1 paul snooker 1.1K Apr 8 18:47 data.odt
-rw-r--r--. 1 paul paul 626K Apr 8 18:46 file1
-rw-r--r--. 1 root tennis 185 Apr 8 18:46 file2
-rw-rw-r--. 1 root root 0 Apr 8 18:47 stuff.txt
paul@rhel65:~/owners$
User paul owns three files; file1 has paul as user owner and has the group paul as group
owner, data.odt is group owned by the group snooker, file2 by the group tennis.
The last file is called stuff.txt and is owned by the root user and the root group.
1.1.2. listing user accounts
You can use the following command to list all local user accounts.
paul@debian7~$ cut -d: -f1 /etc/passwd | column
root ntp sam bert naomi
daemon mysql tom rino matthias2
bin paul wouter antonio bram
sys maarten robrecht simon fabrice
sync kevin bilal sven chimene
games yuri dimitri wouter2 messagebus
man william ahmed tarik roger
lp yves dylan jan frank
mail kris robin ian toon
news hamid matthias ivan rinus
uucp vladimir ben azeddine eddy
proxy abiy mike eric bram2
www-data david kevin2 kamel keith
backup chahid kenzo ischa jesse
list stef aaron bart frederick
irc joeri lorenzo omer hans
gnats glenn jens kurt dries
nobody yannick ruben steve steve2
libuuid christof jelle constantin tomas
Debian-exim george stefaan sam2 johan
statd joost marc bjorn tom2
sshd arno thomas ronald
4
standard file permissions
1.1.3. chgrp
You can change the group owner of a file using the chgrp command.
root@rhel65:/home/paul/owners# ls -l file2
-rw-r--r--. 1 root tennis 185 Apr 8 18:46 file2
root@rhel65:/home/paul/owners# chgrp snooker file2
root@rhel65:/home/paul/owners# ls -l file2
-rw-r--r--. 1 root snooker 185 Apr 8 18:46 file2
root@rhel65:/home/paul/owners#
1.1.4. chown
The user owner of a file can be changed with chown command.
root@laika:/home/paul# ls -l FileForPaul
-rw-r--r-- 1 root paul 0 2008-08-06 14:11 FileForPaul
root@laika:/home/paul# chown paul FileForPaul
root@laika:/home/paul# ls -l FileForPaul
-rw-r--r-- 1 paul paul 0 2008-08-06 14:11 FileForPaul
You can also use chown to change both the user owner and the group owner.
root@laika:/home/paul# ls -l FileForPaul
-rw-r--r-- 1 paul paul 0 2008-08-06 14:11 FileForPaul
root@laika:/home/paul# chown root:project42 FileForPaul
root@laika:/home/paul# ls -l FileForPaul
-rw-r--r-- 1 root project42 0 2008-08-06 14:11 FileForPaul
5
standard file permissions
1.2. list of special files
When you use ls -l, for each file you can see ten characters before the user and group owner.
The first character tells us the type of file. Regular files get a -, directories get a d, symbolic
links are shown with an l, pipes get a p, character devices a c, block devices a b, and sockets
an s.
Table 1.1. Unix special files
first character file type
- normal file
d directory
l symbolic link
p named pipe
b block device
c character device
s socket
Below a screenshot of a character device (the console) and a block device (the hard disk).
paul@debian6lt~$ ls -ld /dev/console /dev/sda
crw------- 1 root root 5, 1 Mar 15 12:45 /dev/console
brw-rw---- 1 root disk 8, 0 Mar 15 12:45 /dev/sda
And here you can see a directory, a regular file and a symbolic link.
paul@debian6lt~$ ls -ld /etc /etc/hosts /etc/motd
drwxr-xr-x 128 root root 12288 Mar 15 18:34 /etc
-rw-r--r-- 1 root root 372 Dec 10 17:36 /etc/hosts
lrwxrwxrwx 1 root root 13 Dec 5 10:36 /etc/motd -> /var/run/motd
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standard file permissions
1.3. permissions
1.3.1. rwx
The nine characters following the file type denote the permissions in three triplets. A
permission can be r for read access, w for write access, and x for execute. You need the r
permission to list (ls) the contents of a directory. You need the x permission to enter (cd) a
directory. You need the w permission to create files in or remove files from a directory.
Table 1.2. standard Unix file permissions
permission on a file on a directory
r (read) read file contents (cat) read directory contents (ls)
w (write) change file contents (vi) create files in (touch)
x (execute) execute the file enter the directory (cd)
1.3.2. three sets of rwx
We already know that the output of ls -l starts with ten characters for each file. This
screenshot shows a regular file (because the first character is a - ).
paul@RHELv4u4:~/test$ ls -l proc42.bash
-rwxr-xr-- 1 paul proj 984 Feb 6 12:01 proc42.bash
Below is a table describing the function of all ten characters.
Table 1.3. Unix file permissions position
position characters function
1 - this is a regular file
2-4 rwx permissions for the user owner
5-7 r-x permissions for the group owner
8-10 r-- permissions for others
When you are the user owner of a file, then the user owner permissions apply to you. The
rest of the permissions have no influence on your access to the file.
When you belong to the group that is the group owner of a file, then the group owner
permissions apply to you. The rest of the permissions have no influence on your access to
the file.
When you are not the user owner of a file and you do not belong to the group owner, then
the others permissions apply to you. The rest of the permissions have no influence on your
access to the file.
7
standard file permissions
1.3.3. permission examples
Some example combinations on files and directories are seen in this screenshot. The name
of the file explains the permissions.
paul@laika:~/perms$ ls -lh
total 12K
drwxr-xr-x 2 paul paul 4.0K 2007-02-07 22:26 AllEnter_UserCreateDelete
-rwxrwxrwx 1 paul paul 0 2007-02-07 22:21 EveryoneFullControl.txt
-r--r----- 1 paul paul 0 2007-02-07 22:21 OnlyOwnersRead.txt
-rwxrwx--- 1 paul paul 0 2007-02-07 22:21 OwnersAll_RestNothing.txt
dr-xr-x--- 2 paul paul 4.0K 2007-02-07 22:25 UserAndGroupEnter
dr-x------ 2 paul paul 4.0K 2007-02-07 22:25 OnlyUserEnter
paul@laika:~/perms$
To summarise, the first rwx triplet represents the permissions for the user owner. The
second triplet corresponds to the group owner; it specifies permissions for all members
of that group. The third triplet defines permissions for all other users that are not the user
owner and are not a member of the group owner.
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standard file permissions
1.3.4. setting permissions (chmod)
Permissions can be changed with chmod. The first example gives the user owner execute
permissions.
paul@laika:~/perms$ ls -l permissions.txt
-rw-r--r-- 1 paul paul 0 2007-02-07 22:34 permissions.txt
paul@laika:~/perms$ chmod u+x permissions.txt
paul@laika:~/perms$ ls -l permissions.txt
-rwxr--r-- 1 paul paul 0 2007-02-07 22:34 permissions.txt
This example removes the group owners read permission.
paul@laika:~/perms$ chmod g-r permissions.txt
paul@laika:~/perms$ ls -l permissions.txt
-rwx---r-- 1 paul paul 0 2007-02-07 22:34 permissions.txt
This example removes the others read permission.
paul@laika:~/perms$ chmod o-r permissions.txt
paul@laika:~/perms$ ls -l permissions.txt
-rwx------ 1 paul paul 0 2007-02-07 22:34 permissions.txt
This example gives all of them the write permission.
paul@laika:~/perms$ chmod a+w permissions.txt
paul@laika:~/perms$ ls -l permissions.txt
-rwx-w--w- 1 paul paul 0 2007-02-07 22:34 permissions.txt
You don't even have to type the a.
paul@laika:~/perms$ chmod +x permissions.txt
paul@laika:~/perms$ ls -l permissions.txt
-rwx-wx-wx 1 paul paul 0 2007-02-07 22:34 permissions.txt
You can also set explicit permissions.
paul@laika:~/perms$ chmod u=rw permissions.txt
paul@laika:~/perms$ ls -l permissions.txt
-rw--wx-wx 1 paul paul 0 2007-02-07 22:34 permissions.txt
Feel free to make any kind of combination.
paul@laika:~/perms$ chmod u=rw,g=rw,o=r permissions.txt
paul@laika:~/perms$ ls -l permissions.txt
-rw-rw-r-- 1 paul paul 0 2007-02-07 22:34 permissions.txt
Even fishy combinations are accepted by chmod.
paul@laika:~/perms$ chmod u=rwx,ug+rw,o=r permissions.txt
paul@laika:~/perms$ ls -l permissions.txt
-rwxrw-r-- 1 paul paul 0 2007-02-07 22:34 permissions.txt
9
standard file permissions
1.3.5. setting octal permissions
Most Unix administrators will use the old school octal system to talk about and set
permissions. Look at the triplet bitwise, equating r to 4, w to 2, and x to 1.
Table 1.4. Octal permissions
binary octal permission
000 0 ---
001 1 --x
010 2 -w-
011 3 -wx
100 4 r--
101 5 r-x
110 6 rw-
111 7 rwx
This makes 777 equal to rwxrwxrwx and by the same logic, 654 mean rw-r-xr-- . The chmod
command will accept these numbers.
paul@laika:~/perms$ chmod 777 permissions.txt
paul@laika:~/perms$ ls -l permissions.txt
-rwxrwxrwx 1 paul paul 0 2007-02-07 22:34 permissions.txt
paul@laika:~/perms$ chmod 664 permissions.txt
paul@laika:~/perms$ ls -l permissions.txt
-rw-rw-r-- 1 paul paul 0 2007-02-07 22:34 permissions.txt
paul@laika:~/perms$ chmod 750 permissions.txt
paul@laika:~/perms$ ls -l permissions.txt
-rwxr-x--- 1 paul paul 0 2007-02-07 22:34 permissions.txt
10
standard file permissions
1.3.6. umask
When creating a file or directory, a set of default permissions are applied. These default
permissions are determined by the umask. The umask specifies permissions that you do
not want set on by default. You can display the umask with the umask command.
[Harry@RHEL4b ~]$ umask
0002
[Harry@RHEL4b ~]$ touch test
[Harry@RHEL4b ~]$ ls -l test
-rw-rw-r-- 1 Harry Harry 0 Jul 24 06:03 test
[Harry@RHEL4b ~]$
As you can also see, the file is also not executable by default. This is a general security
feature among Unixes; newly created files are never executable by default. You have to
explicitly do a chmod +x to make a file executable. This also means that the 1 bit in the
umask has no meaning--a umask of 0022 is the same as 0033.
1.3.7. mkdir -m
When creating directories with mkdir you can use the -m option to set the mode. This
screenshot explains.
paul@debian5~$ mkdir -m 700 MyDir
paul@debian5~$ mkdir -m 777 Public
paul@debian5~$ ls -dl MyDir/ Public/
drwx------ 2 paul paul 4096 2011-10-16 19:16 MyDir/
drwxrwxrwx 2 paul paul 4096 2011-10-16 19:16 Public/
1.3.8. cp -p
To preserve permissions and time stamps from source files, use cp -p.
paul@laika:~/perms$ cp file* cp
paul@laika:~/perms$ cp -p file* cpp
paul@laika:~/perms$ ll *
-rwx------ 1 paul paul 0 2008-08-25 13:26 file33
-rwxr-x--- 1 paul paul 0 2008-08-25 13:26 file42
cp:
total 0
-rwx------ 1 paul paul 0 2008-08-25 13:34 file33
-rwxr-x--- 1 paul paul 0 2008-08-25 13:34 file42
cpp:
total 0
-rwx------ 1 paul paul 0 2008-08-25 13:26 file33
-rwxr-x--- 1 paul paul 0 2008-08-25 13:26 file42
11
standard file permissions
1.4. practice: standard file permissions
1. As normal user, create a directory ~/permissions. Create a file owned by yourself in there.
2. Copy a file owned by root from /etc/ to your permissions dir, who owns this file now ?
3. As root, create a file in the users ~/permissions directory.
4. As normal user, look at who owns this file created by root.
5. Change the ownership of all files in ~/permissions to yourself.
6. Make sure you have all rights to these files, and others can only read.
7. With chmod, is 770 the same as rwxrwx--- ?
8. With chmod, is 664 the same as r-xr-xr-- ?
9. With chmod, is 400 the same as r-------- ?
10. With chmod, is 734 the same as rwxr-xr-- ?
11a. Display the umask in octal and in symbolic form.
11b. Set the umask to 077, but use the symbolic format to set it. Verify that this works.
12. Create a file as root, give only read to others. Can a normal user read this file ? Test
writing to this file with vi.
13a. Create a file as normal user, give only read to others. Can another normal user read this
file ? Test writing to this file with vi.
13b. Can root read this file ? Can root write to this file with vi ?
14. Create a directory that belongs to a group, where every member of that group can read
and write to files, and create files. Make sure that people can only delete their own files.
12
standard file permissions
1.5. solution: standard file permissions
1. As normal user, create a directory ~/permissions. Create a file owned by yourself in there.
mkdir ~/permissions ; touch ~/permissions/myfile.txt
2. Copy a file owned by root from /etc/ to your permissions dir, who owns this file now ?
cp /etc/hosts ~/permissions/
The copy is owned by you.
3. As root, create a file in the users ~/permissions directory.
(become root)# touch /home/username/permissions/rootfile
4. As normal user, look at who owns this file created by root.
ls -l ~/permissions
The file created by root is owned by root.
5. Change the ownership of all files in ~/permissions to yourself.
chown user ~/permissions/*
You cannot become owner of the file that belongs to root.
6. Make sure you have all rights to these files, and others can only read.
chmod 644 (on files)
chmod 755 (on directories)
7. With chmod, is 770 the same as rwxrwx--- ?
yes
8. With chmod, is 664 the same as r-xr-xr-- ?
No
9. With chmod, is 400 the same as r-------- ?
yes
10. With chmod, is 734 the same as rwxr-xr-- ?
no
11a. Display the umask in octal and in symbolic form.
umask ; umask -S
11b. Set the umask to 077, but use the symbolic format to set it. Verify that this works.
umask -S u=rwx,go=
13
standard file permissions
12. Create a file as root, give only read to others. Can a normal user read this file ? Test
writing to this file with vi.
(become root)
# echo hello > /home/username/root.txt
# chmod 744 /home/username/root.txt
(become user)
vi ~/root.txt
13a. Create a file as normal user, give only read to others. Can another normal user read this
file ? Test writing to this file with vi.
echo hello > file ; chmod 744 file
Yes, others can read this file
13b. Can root read this file ? Can root write to this file with vi ?
Yes, root can read and write to this file. Permissions do not apply to root.
14. Create a directory that belongs to a group, where every member of that group can read
and write to files, and create files. Make sure that people can only delete their own files.
mkdir /home/project42 ; groupadd project42
chgrp project42 /home/project42 ; chmod 775 /home/project42
You can not yet do the last part of this exercise...
14
Chapter 2. advanced file permissions
15
advanced file permissions
2.1. sticky bit on directory
You can set the sticky bit on a directory to prevent users from removing files that they do
not own as a user owner. The sticky bit is displayed at the same location as the x permission
for others. The sticky bit is represented by a t (meaning x is also there) or a T (when there
is no x for others).
root@RHELv4u4:~# mkdir /project55
root@RHELv4u4:~# ls -ld /project55
drwxr-xr-x 2 root root 4096 Feb 7 17:38 /project55
root@RHELv4u4:~# chmod +t /project55/
root@RHELv4u4:~# ls -ld /project55
drwxr-xr-t 2 root root 4096 Feb 7 17:38 /project55
root@RHELv4u4:~#
The sticky bit can also be set with octal permissions, it is binary 1 in the first of four triplets.
root@RHELv4u4:~# chmod 1775 /project55/
root@RHELv4u4:~# ls -ld /project55
drwxrwxr-t 2 root root 4096 Feb 7 17:38 /project55
root@RHELv4u4:~#
You will typically find the sticky bit on the /tmp directory.
root@barry:~# ls -ld /tmp
drwxrwxrwt 6 root root 4096 2009-06-04 19:02 /tmp
2.2. setgid bit on directory
setgid can be used on directories to make sure that all files inside the directory are owned
by the group owner of the directory. The setgid bit is displayed at the same location as the x
permission for group owner. The setgid bit is represented by an s (meaning x is also there)
or a S (when there is no x for the group owner). As this example shows, even though root
does not belong to the group proj55, the files created by root in /project55 will belong to
proj55 since the setgid is set.
root@RHELv4u4:~# groupadd proj55
root@RHELv4u4:~# chown root:proj55 /project55/
root@RHELv4u4:~# chmod 2775 /project55/
root@RHELv4u4:~# touch /project55/fromroot.txt
root@RHELv4u4:~# ls -ld /project55/
drwxrwsr-x 2 root proj55 4096 Feb 7 17:45 /project55/
root@RHELv4u4:~# ls -l /project55/
total 4
-rw-r--r-- 1 root proj55 0 Feb 7 17:45 fromroot.txt
root@RHELv4u4:~#
You can use the find command to find all setgid directories.
paul@laika:~$ find / -type d -perm -2000 2> /dev/null
/var/log/mysql
/var/log/news
/var/local
...
16
advanced file permissions
2.3. setgid and setuid on regular files
These two permissions cause an executable file to be executed with the permissions of the
file owner instead of the executing owner. This means that if any user executes a program
that belongs to the root user, and the setuid bit is set on that program, then the program
runs as root. This can be dangerous, but sometimes this is good for security.
Take the example of passwords; they are stored in /etc/shadow which is only readable by
root. (The root user never needs permissions anyway.)
root@RHELv4u4:~# ls -l /etc/shadow
-r-------- 1 root root 1260 Jan 21 07:49 /etc/shadow
Changing your password requires an update of this file, so how can normal non-root users
do this? Let's take a look at the permissions on the /usr/bin/passwd.
root@RHELv4u4:~# ls -l /usr/bin/passwd
-r-s--x--x 1 root root 21200 Jun 17 2005 /usr/bin/passwd
When running the passwd program, you are executing it with root credentials.
You can use the find command to find all setuid programs.
paul@laika:~$ find /usr/bin -type f -perm -04000
/usr/bin/arping
/usr/bin/kgrantpty
/usr/bin/newgrp
/usr/bin/chfn
/usr/bin/sudo
/usr/bin/fping6
/usr/bin/passwd
/usr/bin/gpasswd
...
In most cases, setting the setuid bit on executables is sufficient. Setting the setgid bit will
result in these programs to run with the credentials of their group owner.
2.4. setuid on sudo
The sudo binary has the setuid bit set, so any user can run it with the effective userid of root.
paul@rhel65:~$ ls -l $(which sudo)
---s--x--x. 1 root root 123832 Oct 7 2013 /usr/bin/sudo
paul@rhel65:~$
17
advanced file permissions
2.5. practice: sticky, setuid and setgid bits
1a. Set up a directory, owned by the group sports.
1b. Members of the sports group should be able to create files in this directory.
1c. All files created in this directory should be group-owned by the sports group.
1d. Users should be able to delete only their own user-owned files.
1e. Test that this works!
2. Verify the permissions on /usr/bin/passwd. Remove the setuid, then try changing your
password as a normal user. Reset the permissions back and try again.
3. If time permits (or if you are waiting for other students to finish this practice), read about
file attributes in the man page of chattr and lsattr. Try setting the i attribute on a file and
test that it works.
18
advanced file permissions
2.6. solution: sticky, setuid and setgid bits
1a. Set up a directory, owned by the group sports.
groupadd sports
mkdir /home/sports
chown root:sports /home/sports
1b. Members of the sports group should be able to create files in this directory.
chmod 770 /home/sports
1c. All files created in this directory should be group-owned by the sports group.
chmod 2770 /home/sports
1d. Users should be able to delete only their own user-owned files.
chmod +t /home/sports
1e. Test that this works!
Log in with different users (group members and others and root), create files and watch the
permissions. Try changing and deleting files...
2. Verify the permissions on /usr/bin/passwd. Remove the setuid, then try changing your
password as a normal user. Reset the permissions back and try again.
root@deb503:~# ls -l /usr/bin/passwd
-rwsr-xr-x 1 root root 31704 2009-11-14 15:41 /usr/bin/passwd
root@deb503:~# chmod 755 /usr/bin/passwd
root@deb503:~# ls -l /usr/bin/passwd
-rwxr-xr-x 1 root root 31704 2009-11-14 15:41 /usr/bin/passwd
A normal user cannot change password now.
root@deb503:~# chmod 4755 /usr/bin/passwd
root@deb503:~# ls -l /usr/bin/passwd
-rwsr-xr-x 1 root root 31704 2009-11-14 15:41 /usr/bin/passwd
3. If time permits (or if you are waiting for other students to finish this practice), read about
file attributes in the man page of chattr and lsattr. Try setting the i attribute on a file and
test that it works.
paul@laika:~$ sudo su -
[sudo] password for paul:
root@laika:~# mkdir attr
root@laika:~# cd attr/
root@laika:~/attr# touch file42
root@laika:~/attr# lsattr
------------------ ./file42
root@laika:~/attr# chattr +i file42
19
advanced file permissions
root@laika:~/attr# lsattr
----i------------- ./file42
root@laika:~/attr# rm -rf file42
rm: cannot remove `file42': Operation not permitted
root@laika:~/attr# chattr -i file42
root@laika:~/attr# rm -rf file42
root@laika:~/attr#
20
Chapter 3. access control lists
Standard Unix permissions might not be enough for some organisations. This chapter
introduces access control lists or acl's to further protect files and directories.
21
access control lists
3.1. acl in /etc/fstab
File systems that support access control lists, or acls, have to be mounted with the acl
option listed in /etc/fstab. In the example below, you can see that the root file system has
acl support, whereas /home/data does not.
root@laika:~# tail -4 /etc/fstab
/dev/sda1 / ext3 acl,relatime 0 1
/dev/sdb2 /home/data auto noacl,defaults 0 0
pasha:/home/r /home/pasha nfs defaults 0 0
wolf:/srv/data /home/wolf nfs defaults 0 0
3.2. getfacl
Reading acls can be done with /usr/bin/getfacl. This screenshot shows how to read the acl
of file33 with getfacl.
paul@laika:~/test$ getfacl file33
# file: file33
# owner: paul
# group: paul
user::rw-
group::r--
mask::rwx
other::r--
3.3. setfacl
Writing or changing acls can be done with /usr/bin/setfacl. These screenshots show how
to change the acl of file33 with setfacl.
First we add user sandra with octal permission 7 to the acl.
paul@laika:~/test$ setfacl -m u:sandra:7 file33
Then we add the group tennis with octal permission 6 to the acl of the same file.
paul@laika:~/test$ setfacl -m g:tennis:6 file33
The result is visible with getfacl.
paul@laika:~/test$ getfacl file33
# file: file33
# owner: paul
# group: paul
user::rw-
user:sandra:rwx
group::r--
group:tennis:rw-
mask::rwx
other::r--
22
access control lists
3.4. remove an acl entry
The -x option of the setfacl command will remove an acl entry from the targeted file.
paul@laika:~/test$ setfacl -m u:sandra:7 file33
paul@laika:~/test$ getfacl file33 | grep sandra
user:sandra:rwx
paul@laika:~/test$ setfacl -x sandra file33
paul@laika:~/test$ getfacl file33 | grep sandra
Note that omitting the u or g when defining the acl for an account will default it to a user
account.
3.5. remove the complete acl
The -b option of the setfacl command will remove the acl from the targeted file.
paul@laika:~/test$ setfacl -b file33
paul@laika:~/test$ getfacl file33
# file: file33
# owner: paul
# group: paul
user::rw-
group::r--
other::r--
3.6. the acl mask
The acl mask defines the maximum effective permissions for any entry in the acl. This
mask is calculated every time you execute the setfacl or chmod commands.
You can prevent the calculation by using the --no-mask switch.
paul@laika:~/test$ setfacl --no-mask -m u:sandra:7 file33
paul@laika:~/test$ getfacl file33
# file: file33
# owner: paul
# group: paul
user::rw-
user:sandra:rwx #effective:rw-
group::r--
mask::rw-
other::r--
23
access control lists
3.7. eiciel
Desktop users might want to use eiciel to manage acls with a graphical tool.
You will need to install eiciel and nautilus-actions to have an extra tab in nautilus to
manage acls.
paul@laika:~$ sudo aptitude install eiciel nautilus-actions
24
Chapter 4. file links
An average computer using Linux has a file system with many hard links and symbolic
links.
To understand links in a file system, you first have to understand what an inode is.
25
file links
4.1. inodes
4.1.1. inode contents
An inode is a data structure that contains metadata about a file. When the file system stores
a new file on the hard disk, it stores not only the contents (data) of the file, but also extra
properties like the name of the file, the creation date, its permissions, the owner of the file,
and more. All this information (except the name of the file and the contents of the file) is
stored in the inode of the file.
The ls -l command will display some of the inode contents, as seen in this screenshot.
root@rhel53 ~# ls -ld /home/project42/
drwxr-xr-x 4 root pro42 4.0K Mar 27 14:29 /home/project42/
4.1.2. inode table
The inode table contains all of the inodes and is created when you create the file system
(with mkfs). You can use the df -i command to see how many inodes are used and free on
mounted file systems.
root@rhel53 ~# df -i
Filesystem Inodes IUsed IFree IUse% Mounted on
/dev/mapper/VolGroup00-LogVol00
4947968 115326 4832642 3% /
/dev/hda1 26104 45 26059 1% /boot
tmpfs 64417 1 64416 1% /dev/shm
/dev/sda1 262144 2207 259937 1% /home/project42
/dev/sdb1 74400 5519 68881 8% /home/project33
/dev/sdb5 0 0 0 - /home/sales
/dev/sdb6 100744 11 100733 1% /home/research
In the df -i screenshot above you can see the inode usage for several mounted file systems.
You don't see numbers for /dev/sdb5 because it is a fat file system.
4.1.3. inode number
Each inode has a unique number (the inode number). You can see the inode numbers with
the ls -li command.
paul@RHELv4u4:~/test$ touch file1
paul@RHELv4u4:~/test$ touch file2
paul@RHELv4u4:~/test$ touch file3
paul@RHELv4u4:~/test$ ls -li
total 12
817266 -rw-rw-r-- 1 paul paul 0 Feb 5 15:38 file1
817267 -rw-rw-r-- 1 paul paul 0 Feb 5 15:38 file2
817268 -rw-rw-r-- 1 paul paul 0 Feb 5 15:38 file3
paul@RHELv4u4:~/test$
These three files were created one after the other and got three different inodes (the first
column). All the information you see with this ls command resides in the inode, except for
the filename (which is contained in the directory).
26
file links
4.1.4. inode and file contents
Let's put some data in one of the files.
paul@RHELv4u4:~/test$ ls -li
total 16
817266 -rw-rw-r-- 1 paul paul 0 Feb 5 15:38 file1
817270 -rw-rw-r-- 1 paul paul 92 Feb 5 15:42 file2
817268 -rw-rw-r-- 1 paul paul 0 Feb 5 15:38 file3
paul@RHELv4u4:~/test$ cat file2
It is winter now and it is very cold.
We do not like the cold, we prefer hot summer nights.
paul@RHELv4u4:~/test$
The data that is displayed by the cat command is not in the inode, but somewhere else on
the disk. The inode contains a pointer to that data.
4.2. about directories
4.2.1. a directory is a table
A directory is a special kind of file that contains a table which maps filenames to inodes.
Listing our current directory with ls -ali will display the contents of the directory file.
paul@RHELv4u4:~/test$ ls -ali
total 32
817262 drwxrwxr-x 2 paul paul 4096 Feb 5 15:42 .
800768 drwx------ 16 paul paul 4096 Feb 5 15:42 ..
817266 -rw-rw-r-- 1 paul paul 0 Feb 5 15:38 file1
817270 -rw-rw-r-- 1 paul paul 92 Feb 5 15:42 file2
817268 -rw-rw-r-- 1 paul paul 0 Feb 5 15:38 file3
paul@RHELv4u4:~/test$
4.2.2. . and ..
You can see five names, and the mapping to their five inodes. The dot . is a mapping to itself,
and the dotdot .. is a mapping to the parent directory. The three other names are mappings
to different inodes.
27
file links
4.3. hard links
4.3.1. creating hard links
When we create a hard link to a file with ln, an extra entry is added in the directory. A new
file name is mapped to an existing inode.
paul@RHELv4u4:~/test$ ln file2 hardlink_to_file2
paul@RHELv4u4:~/test$ ls -li
total 24
817266 -rw-rw-r-- 1 paul paul 0 Feb 5 15:38 file1
817270 -rw-rw-r-- 2 paul paul 92 Feb 5 15:42 file2
817268 -rw-rw-r-- 1 paul paul 0 Feb 5 15:38 file3
817270 -rw-rw-r-- 2 paul paul 92 Feb 5 15:42 hardlink_to_file2
paul@RHELv4u4:~/test$
Both files have the same inode, so they will always have the same permissions and the same
owner. Both files will have the same content. Actually, both files are equal now, meaning
you can safely remove the original file, the hardlinked file will remain. The inode contains
a counter, counting the number of hard links to itself. When the counter drops to zero, then
the inode is emptied.
4.3.2. finding hard links
You can use the find command to look for files with a certain inode. The screenshot below
shows how to search for all filenames that point to inode 817270. Remember that an inode
number is unique to its partition.
paul@RHELv4u4:~/test$ find / -inum 817270 2> /dev/null
/home/paul/test/file2
/home/paul/test/hardlink_to_file2
28
file links
4.4. symbolic links
Symbolic links (sometimes called soft links) do not link to inodes, but create a name to
name mapping. Symbolic links are created with ln -s. As you can see below, the symbolic
link gets an inode of its own.
paul@RHELv4u4:~/test$ ln -s file2 symlink_to_file2
paul@RHELv4u4:~/test$ ls -li
total 32
817273 -rw-rw-r-- 1 paul paul 13 Feb 5 17:06 file1
817270 -rw-rw-r-- 2 paul paul 106 Feb 5 17:04 file2
817268 -rw-rw-r-- 1 paul paul 0 Feb 5 15:38 file3
817270 -rw-rw-r-- 2 paul paul 106 Feb 5 17:04 hardlink_to_file2
817267 lrwxrwxrwx 1 paul paul 5 Feb 5 16:55 symlink_to_file2 -> file2
paul@RHELv4u4:~/test$
Permissions on a symbolic link have no meaning, since the permissions of the target apply.
Hard links are limited to their own partition (because they point to an inode), symbolic links
can link anywhere (other file systems, even networked).
4.5. removing links
Links can be removed with rm.
paul@laika:~$ touch data.txt
paul@laika:~$ ln -s data.txt sl_data.txt
paul@laika:~$ ln data.txt hl_data.txt
paul@laika:~$ rm sl_data.txt
paul@laika:~$ rm hl_data.txt
29
file links
4.6. practice : links
1. Create two files named winter.txt and summer.txt, put some text in them.
2. Create a hard link to winter.txt named hlwinter.txt.
3. Display the inode numbers of these three files, the hard links should have the same inode.
4. Use the find command to list the two hardlinked files
5. Everything about a file is in the inode, except two things : name them!
6. Create a symbolic link to summer.txt called slsummer.txt.
7. Find all files with inode number 2. What does this information tell you ?
8. Look at the directories /etc/init.d/ /etc/rc2.d/ /etc/rc3.d/ ... do you see the links ?
9. Look in /lib with ls -l...
10. Use find to look in your home directory for regular files that do not(!) have one hard link.
30
file links
4.7. solution : links
1. Create two files named winter.txt and summer.txt, put some text in them.
echo cold > winter.txt ; echo hot > summer.txt
2. Create a hard link to winter.txt named hlwinter.txt.
ln winter.txt hlwinter.txt
3. Display the inode numbers of these three files, the hard links should have the same inode.
ls -li winter.txt summer.txt hlwinter.txt
4. Use the find command to list the two hardlinked files
find . -inum xyz #replace xyz with the inode number
5. Everything about a file is in the inode, except two things : name them!
The name of the file is in a directory, and the contents is somewhere on the disk.
6. Create a symbolic link to summer.txt called slsummer.txt.
ln -s summer.txt slsummer.txt
7. Find all files with inode number 2. What does this information tell you ?
It tells you there is more than one inode table (one for every formatted partition + virtual
file systems)
8. Look at the directories /etc/init.d/ /etc/rc.d/ /etc/rc3.d/ ... do you see the links ?
ls -l /etc/init.d
ls -l /etc/rc2.d
ls -l /etc/rc3.d
9. Look in /lib with ls -l...
ls -l /lib
10. Use find to look in your home directory for regular files that do not(!) have one hard link.
find ~ ! -links 1 -type f
31
Part II. disk management
Table of Contents
5. disk devices ............................................................................................................................................... 35
5.1. terminology ................................................................................................................................... 36
5.2. device naming ............................................................................................................................... 38
5.3. discovering disk devices ............................................................................................................... 39
5.4. erasing a hard disk ........................................................................................................................ 44
5.5. advanced hard disk settings .......................................................................................................... 45
5.6. practice: hard disk devices ........................................................................................................... 46
5.7. solution: hard disk devices ........................................................................................................... 47
6. disk partitions .......................................................................................................................................... 49
6.1. about partitions .............................................................................................................................. 50
6.2. discovering partitions .................................................................................................................... 51
6.3. partitioning new disks ................................................................................................................... 53
6.4. about the partition table ................................................................................................................ 55
6.5. GUID partition table ..................................................................................................................... 56
6.6. labeling with parted ...................................................................................................................... 56
6.7. practice: partitions ......................................................................................................................... 58
6.8. solution: partitions ......................................................................................................................... 59
7. file systems ................................................................................................................................................ 60
7.1. about file systems ......................................................................................................................... 61
7.2. common file systems .................................................................................................................... 62
7.3. putting a file system on a partition .............................................................................................. 65
7.4. tuning a file system ...................................................................................................................... 66
7.5. checking a file system .................................................................................................................. 67
7.6. practice: file systems ..................................................................................................................... 68
7.7. solution: file systems .................................................................................................................... 69
8. mounting ................................................................................................................................................... 70
8.1. mounting local file systems .......................................................................................................... 71
8.2. displaying mounted file systems .................................................................................................. 72
8.3. from start to finish ........................................................................................................................ 74
8.4. permanent mounts ......................................................................................................................... 75
8.5. securing mounts ............................................................................................................................ 76
8.6. mounting remote file systems ....................................................................................................... 77
8.7. practice: mounting file systems .................................................................................................... 78
8.8. solution: mounting file systems .................................................................................................... 79
9. troubleshooting tools ............................................................................................................................... 81
9.1. lsof ................................................................................................................................................. 82
9.2. fuser ............................................................................................................................................... 83
9.3. chroot ............................................................................................................................................. 84
9.4. iostat .............................................................................................................................................. 85
9.5. iotop ............................................................................................................................................... 86
9.6. vmstat ............................................................................................................................................ 87
9.7. practice: troubleshooting tools ...................................................................................................... 88
9.8. solution: troubleshooting tools ...................................................................................................... 89
10. introduction to uuid's ............................................................................................................................ 90
10.1. about unique objects ................................................................................................................... 91
10.2. tune2fs ......................................................................................................................................... 91
10.3. uuid .............................................................................................................................................. 91
10.4. uuid in /etc/fstab .......................................................................................................................... 92
10.5. uuid as a boot device .................................................................................................................. 93
10.6. practice: uuid and filesystems .................................................................................................... 94
10.7. solution: uuid and filesystems .................................................................................................... 95
11. introduction to raid ............................................................................................................................... 96
11.1. hardware or software .................................................................................................................. 96
11.2. raid levels .................................................................................................................................... 97
11.3. building a software raid5 array ................................................................................................... 99
33
disk management
11.4. practice: raid .............................................................................................................................. 102
11.5. solution: raid ............................................................................................................................. 103
12. logical volume management ............................................................................................................... 104
12.1. introduction to lvm ................................................................................................................... 105
12.2. lvm terminology ........................................................................................................................ 106
12.3. example: using lvm ................................................................................................................... 107
12.4. example: extend a logical volume ............................................................................................ 109
12.5. example: resize a physical Volume .......................................................................................... 111
12.6. example: mirror a logical volume ............................................................................................ 113
12.7. example: snapshot a logical volume ......................................................................................... 114
12.8. verifying existing physical volumes ......................................................................................... 115
12.9. verifying existing volume groups ............................................................................................. 117
12.10. verifying existing logical volumes .......................................................................................... 118
12.11. manage physical volumes ....................................................................................................... 119
12.12. manage volume groups ........................................................................................................... 121
12.13. manage logical volumes .......................................................................................................... 123
12.14. practice : lvm ........................................................................................................................... 125
12.15. solution : lvm .......................................................................................................................... 126
13. iSCSI devices ........................................................................................................................................ 130
13.1. iSCSI terminology ..................................................................................................................... 131
13.2. iSCSI Target in RHEL/CentOS ................................................................................................ 131
13.3. iSCSI Initiator in RHEL/CentOS ............................................................................................. 133
13.4. iSCSI target on Debian ............................................................................................................. 135
13.5. iSCSI target setup with dd files ............................................................................................... 136
13.6. ISCSI initiator on ubuntu .......................................................................................................... 138
13.7. using iSCSI devices .................................................................................................................. 140
13.8. iSCSI Target RHEL7/CentOS7 ................................................................................................ 141
13.9. iSCSI Initiator RHEL7/CentOS7 .............................................................................................. 143
13.10. practice: iSCSI devices ........................................................................................................... 145
13.11. solution: iSCSI devices ........................................................................................................... 146
14. introduction to multipathing .............................................................................................................. 150
14.1. install multipath ......................................................................................................................... 151
14.2. configure multipath ................................................................................................................... 151
14.3. network ...................................................................................................................................... 152
14.4. start multipathd and iscsi .......................................................................................................... 152
14.5. multipath list ............................................................................................................................. 154
14.6. using the device ........................................................................................................................ 155
14.7. practice: multipathing ............................................................................................................... 156
14.8. solution: multipathing ............................................................................................................... 157
34
Chapter 5. disk devices
This chapter teaches you how to locate and recognise hard disk devices. This prepares you
for the next chapter, where we put partitions on these devices.
35
disk devices
5.1. terminology
5.1.1. platter, head, track, cylinder, sector
Data is commonly stored on magnetic or optical disk platters. The platters are rotated (at
high speeds). Data is read by heads, which are very close to the surface of the platter, without
touching it! The heads are mounted on an arm (sometimes called a comb or a fork).
Data is written in concentric circles called tracks. Track zero is (usually) on the outside.
The time it takes to position the head over a certain track is called the seek time. Often
the platters are stacked on top of each other, hence the set of tracks accessible at a certain
position of the comb forms a cylinder. Tracks are divided into 512 byte sectors, with more
unused space (gap) between the sectors on the outside of the platter.
When you break down the advertised access time of a hard drive, you will notice that most
of that time is taken by movement of the heads (about 65%) and rotational latency (about
30%).
5.1.2. ide or scsi
Actually, the title should be ata or scsi, since ide is an ata compatible device. Most desktops
use ata devices, most servers use scsi.
5.1.3. ata
An ata controller allows two devices per bus, one master and one slave. Unless your
controller and devices support cable select, you have to set this manually with jumpers.
With the introduction of sata (serial ata), the original ata was renamed to parallel ata.
Optical drives often use atapi, which is an ATA interface using the SCSI communication
protocol.
5.1.4. scsi
A scsi controller allows more than two devices. When using SCSI (small computer system
interface), each device gets a unique scsi id. The scsi controller also needs a scsi id, do not
use this id for a scsi-attached device.
Older 8-bit SCSI is now called narrow, whereas 16-bit is wide. When the bus speeds was
doubled to 10Mhz, this was known as fast SCSI. Doubling to 20Mhz made it ultra SCSI.
Take a look at http://en.wikipedia.org/wiki/SCSI for more SCSI standards.
36
disk devices
5.1.5. block device
Random access hard disk devices have an abstraction layer called block device to enable
formatting in fixed-size (usually 512 bytes) blocks. Blocks can be accessed independent of
access to other blocks.
[root@centos65 ~]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 40G 0 disk
--sda1 8:1 0 500M 0 part /boot
--sda2 8:2 0 39.5G 0 part
--VolGroup-lv_root (dm-0) 253:0 0 38.6G 0 lvm /
--VolGroup-lv_swap (dm-1) 253:1 0 928M 0 lvm [SWAP]
sdb 8:16 0 72G 0 disk
sdc 8:32 0 144G 0 disk
A block device has the letter b to denote the file type in the output of ls -l.
[root@centos65 ~]# ls -l /dev/sd*
brw-rw----. 1 root disk 8, 0 Apr 19 10:12 /dev/sda
brw-rw----. 1 root disk 8, 1 Apr 19 10:12 /dev/sda1
brw-rw----. 1 root disk 8, 2 Apr 19 10:12 /dev/sda2
brw-rw----. 1 root disk 8, 16 Apr 19 10:12 /dev/sdb
brw-rw----. 1 root disk 8, 32 Apr 19 10:12 /dev/sdc
Note that a character device is a constant stream of characters, being denoted by a c in ls -
l. Note also that the ISO 9660 standard for cdrom uses a 2048 byte block size.
Old hard disks (and floppy disks) use cylinder-head-sector addressing to access a sector
on the disk. Most current disks use LBA (Logical Block Addressing).
5.1.6. solid state drive
A solid state drive or ssd is a block device without moving parts. It is comparable to flash
memory. An ssd is more expensive than a hard disk, but it typically has a much faster access
time.
In this book we will use the following pictograms for spindle disks (in brown) and solid
state disks (in blue).
37
disk devices
5.2. device naming
5.2.1. ata (ide) device naming
All ata drives on your system will start with /dev/hd followed by a unit letter. The master
hdd on the first ata controller is /dev/hda, the slave is /dev/hdb. For the second controller,
the names of the devices are /dev/hdc and /dev/hdd.
Table 5.1. ide device naming
controller connection device name
master /dev/hda
ide0
slave /dev/hdb
master /dev/hdc
ide1
slave /dev/hdd
It is possible to have only /dev/hda and /dev/hdd. The first one is a single ata hard disk, the
second one is the cdrom (by default configured as slave).
5.2.2. scsi device naming
scsi drives follow a similar scheme, but all start with /dev/sd. When you run out of letters
(after /dev/sdz), you can continue with /dev/sdaa and /dev/sdab and so on. (We will see later
on that lvm volumes are commonly seen as /dev/md0, /dev/md1 etc.)
Below a sample of how scsi devices on a Linux can be named. Adding a scsi disk or raid
controller with a lower scsi address will change the naming scheme (shifting the higher scsi
addresses one letter further in the alphabet).
Table 5.2. scsi device naming
device scsi id device name
disk 0 0 /dev/sda
disk 1 1 /dev/sdb
raid controller 0 5 /dev/sdc
raid controller 1 6 /dev/sdd
A modern Linux system will use /dev/sd* for scsi and sata devices, and also for sd-cards,
usb-sticks, (legacy) ATA/IDE devices and solid state drives.
38
disk devices
5.3. discovering disk devices
5.3.1. fdisk
You can start by using /sbin/fdisk to find out what kind of disks are seen by the kernel.
Below the result on old Debian desktop, with two ata-ide disks present.
root@barry:~# fdisk -l | grep Disk
Disk /dev/hda: 60.0 GB, 60022480896 bytes
Disk /dev/hdb: 81.9 GB, 81964302336 bytes
And here an example of sata and scsi disks on a server with CentOS. Remember that sata
disks are also presented to you with the scsi /dev/sd* notation.
[root@centos65 ~]# fdisk -l | grep 'Disk /dev/sd'
Disk /dev/sda: 42.9 GB, 42949672960 bytes
Disk /dev/sdb: 77.3 GB, 77309411328 bytes
Disk /dev/sdc: 154.6 GB, 154618822656 bytes
Disk /dev/sdd: 154.6 GB, 154618822656 bytes
Here is an overview of disks on a RHEL4u3 server with two real 72GB scsi disks. This
server is attached to a NAS with four NAS disks of half a terabyte. On the NAS disks, four
LVM (/dev/mdx) software RAID devices are configured.
[root@tsvtl1 ~]# fdisk -l | grep Disk
Disk /dev/sda: 73.4 GB, 73407488000 bytes
Disk /dev/sdb: 73.4 GB, 73407488000 bytes
Disk /dev/sdc: 499.0 GB, 499036192768 bytes
Disk /dev/sdd: 499.0 GB, 499036192768 bytes
Disk /dev/sde: 499.0 GB, 499036192768 bytes
Disk /dev/sdf: 499.0 GB, 499036192768 bytes
Disk /dev/md0: 271 MB, 271319040 bytes
Disk /dev/md2: 21.4 GB, 21476081664 bytes
Disk /dev/md3: 21.4 GB, 21467889664 bytes
Disk /dev/md1: 21.4 GB, 21476081664 bytes
You can also use fdisk to obtain information about one specific hard disk device.
[root@centos65 ~]# fdisk -l /dev/sdc
Disk /dev/sdc: 154.6 GB, 154618822656 bytes
255 heads, 63 sectors/track, 18798 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Later we will use fdisk to do dangerous stuff like creating and deleting partitions.
39
disk devices
5.3.2. dmesg
Kernel boot messages can be seen after boot with dmesg. Since hard disk devices are
detected by the kernel during boot, you can also use dmesg to find information about disk
devices.
[root@centos65 ~]# dmesg | grep 'sd[a-z]' | head
sd 0:0:0:0: [sda] 83886080 512-byte logical blocks: (42.9 GB/40.0 GiB)
sd 0:0:0:0: [sda] Write Protect is off
sd 0:0:0:0: [sda] Mode Sense: 00 3a 00 00
sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support \
DPO or FUA
sda: sda1 sda2
sd 0:0:0:0: [sda] Attached SCSI disk
sd 3:0:0:0: [sdb] 150994944 512-byte logical blocks: (77.3 GB/72.0 GiB)
sd 3:0:0:0: [sdb] Write Protect is off
sd 3:0:0:0: [sdb] Mode Sense: 00 3a 00 00
sd 3:0:0:0: [sdb] Write cache: enabled, read cache: enabled, doesn't support \
DPO or FUA
Here is another example of dmesg on a computer with a 200GB ata disk.
paul@barry:~$ dmesg | grep -i "ata disk"
[ 2.624149] hda: ST360021A, ATA DISK drive
[ 2.904150] hdb: Maxtor 6Y080L0, ATA DISK drive
[ 3.472148] hdd: WDC WD2000BB-98DWA0, ATA DISK drive
Third and last example of dmesg running on RHEL5.3.
root@rhel53 ~# dmesg | grep -i "scsi disk"
sd 0:0:2:0: Attached scsi disk sda
sd 0:0:3:0: Attached scsi disk sdb
sd 0:0:6:0: Attached scsi disk sdc
40
disk devices
5.3.3. /sbin/lshw
The lshw tool will list hardware. With the right options lshw can show a lot of information
about disks (and partitions).
Below a truncated screenshot on Debian 6:
root@debian6~# lshw -class volume | grep -A1 -B2 scsi
description: Linux raid autodetect partition
physical id: 1
bus info: scsi@1:0.0.0,1
logical name: /dev/sdb1
--
description: Linux raid autodetect partition
physical id: 1
bus info: scsi@2:0.0.0,1
logical name: /dev/sdc1
--
description: Linux raid autodetect partition
physical id: 1
bus info: scsi@3:0.0.0,1
logical name: /dev/sdd1
--
description: Linux raid autodetect partition
physical id: 1
bus info: scsi@4:0.0.0,1
logical name: /dev/sde1
--
vendor: Linux
physical id: 1
bus info: scsi@0:0.0.0,1
logical name: /dev/sda1
--
vendor: Linux
physical id: 2
bus info: scsi@0:0.0.0,2
logical name: /dev/sda2
--
description: Extended partition
physical id: 3
bus info: scsi@0:0.0.0,3
logical name: /dev/sda3
Redhat and CentOS do not have this tool (unless you add a repository).
41
disk devices
5.3.4. /sbin/lsscsi
The lsscsi command provides a nice readable output of all scsi (and scsi emulated devices).
This first screenshot shows lsscsi on a SPARC system.
root@shaka:~# lsscsi
[0:0:0:0] disk Adaptec RAID5 V1.0 /dev/sda
[1:0:0:0] disk SEAGATE ST336605FSUN36G 0438 /dev/sdb
root@shaka:~#
Below a screenshot of lsscsi on a QNAP NAS (which has four 750GB disks and boots from
a usb stick).
lroot@debian6~# lsscsi
[0:0:0:0] disk SanDisk Cruzer Edge 1.19 /dev/sda
[1:0:0:0] disk ATA ST3750330AS SD04 /dev/sdb
[2:0:0:0] disk ATA ST3750330AS SD04 /dev/sdc
[3:0:0:0] disk ATA ST3750330AS SD04 /dev/sdd
[4:0:0:0] disk ATA ST3750330AS SD04 /dev/sde
This screenshot shows the classic output of lsscsi.
root@debian6~# lsscsi -c
Attached devices:
Host: scsi0 Channel: 00 Target: 00 Lun: 00
Vendor: SanDisk Model: Cruzer Edge Rev: 1.19
Type: Direct-Access ANSI SCSI revision: 02
Host: scsi1 Channel: 00 Target: 00 Lun: 00
Vendor: ATA Model: ST3750330AS Rev: SD04
Type: Direct-Access ANSI SCSI revision: 05
Host: scsi2 Channel: 00 Target: 00 Lun: 00
Vendor: ATA Model: ST3750330AS Rev: SD04
Type: Direct-Access ANSI SCSI revision: 05
Host: scsi3 Channel: 00 Target: 00 Lun: 00
Vendor: ATA Model: ST3750330AS Rev: SD04
Type: Direct-Access ANSI SCSI revision: 05
Host: scsi4 Channel: 00 Target: 00 Lun: 00
Vendor: ATA Model: ST3750330AS Rev: SD04
Type: Direct-Access ANSI SCSI revision: 05
42
disk devices
5.3.5. /proc/scsi/scsi
Another way to locate scsi (or sd) devices is via /proc/scsi/scsi.
This screenshot is from a sparc computer with adaptec RAID5.
root@shaka:~# cat /proc/scsi/scsi
Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
Vendor: Adaptec Model: RAID5 Rev: V1.0
Type: Direct-Access ANSI SCSI revision: 02
Host: scsi1 Channel: 00 Id: 00 Lun: 00
Vendor: SEAGATE Model: ST336605FSUN36G Rev: 0438
Type: Direct-Access ANSI SCSI revision: 03
root@shaka:~#
Here we run cat /proc/scsi/scsi on the QNAP from above (with Debian Linux).
root@debian6~# cat /proc/scsi/scsi
Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
Vendor: SanDisk Model: Cruzer Edge Rev: 1.19
Type: Direct-Access ANSI SCSI revision: 02
Host: scsi1 Channel: 00 Id: 00 Lun: 00
Vendor: ATA Model: ST3750330AS Rev: SD04
Type: Direct-Access ANSI SCSI revision: 05
Host: scsi2 Channel: 00 Id: 00 Lun: 00
Vendor: ATA Model: ST3750330AS Rev: SD04
Type: Direct-Access ANSI SCSI revision: 05
Host: scsi3 Channel: 00 Id: 00 Lun: 00
Vendor: ATA Model: ST3750330AS Rev: SD04
Type: Direct-Access ANSI SCSI revision: 05
Host: scsi4 Channel: 00 Id: 00 Lun: 00
Vendor: ATA Model: ST3750330AS Rev: SD04
Type: Direct-Access ANSI SCSI revision: 05
Note that some recent versions of Debian have this disabled in the kernel. You can enable
it (after a kernel compile) using this entry:
# CONFIG_SCSI_PROC_FS is not set
Redhat and CentOS have this by default (if there are scsi devices present).
[root@centos65 ~]# cat /proc/scsi/scsi
Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
Vendor: ATA Model: VBOX HARDDISK Rev: 1.0
Type: Direct-Access ANSI SCSI revision: 05
Host: scsi3 Channel: 00 Id: 00 Lun: 00
Vendor: ATA Model: VBOX HARDDISK Rev: 1.0
Type: Direct-Access ANSI SCSI revision: 05
Host: scsi4 Channel: 00 Id: 00 Lun: 00
Vendor: ATA Model: VBOX HARDDISK Rev: 1.0
Type: Direct-Access ANSI SCSI revision: 05
43
disk devices
5.4. erasing a hard disk
Before selling your old hard disk on the internet, it may be a good idea to erase it. By simply
repartitioning, or by using the Microsoft Windows format utility, or even after an mkfs
command, some people will still be able to read most of the data on the disk.
root@debian6~# aptitude search foremost autopsy sleuthkit | tr -s ' '
p autopsy - graphical interface to SleuthKit
p foremost - Forensics application to recover data
p sleuthkit - collection of tools for forensics analysis
Although technically the /sbin/badblocks tool is meant to look for bad blocks, you can use
it to completely erase all data from a disk. Since this is really writing to every sector of the
disk, it can take a long time!
root@RHELv4u2:~# badblocks -ws /dev/sdb
Testing with pattern 0xaa: done
Reading and comparing: done
Testing with pattern 0x55: done
Reading and comparing: done
Testing with pattern 0xff: done
Reading and comparing: done
Testing with pattern 0x00: done
Reading and comparing: done
The previous screenshot overwrites every sector of the disk four times. Erasing once with
a tool like dd is enough to destroy all data.
Warning, this screenshot shows how to permanently destroy all data on a block device.
[root@rhel65 ~]# dd if=/dev/zero of=/dev/sdb
44
disk devices
5.5. advanced hard disk settings
Tweaking of hard disk settings (dma, gap, ...) are not covered in this course. Several tools
exists, hdparm and sdparm are two of them.
hdparm can be used to display or set information and parameters about an ATA (or SATA)
hard disk device. The -i and -I options will give you even more information about the
physical properties of the device.
root@laika:~# hdparm /dev/sdb
/dev/sdb:
IO_support = 0 (default 16-bit)
readonly = 0 (off)
readahead = 256 (on)
geometry = 12161/255/63, sectors = 195371568, start = 0
Below hdparm info about a 200GB IDE disk.
root@barry:~# hdparm /dev/hdd
/dev/hdd:
multcount = 0 (off)
IO_support = 0 (default)
unmaskirq = 0 (off)
using_dma = 1 (on)
keepsettings = 0 (off)
readonly = 0 (off)
readahead = 256 (on)
geometry = 24321/255/63, sectors = 390721968, start = 0
Here a screenshot of sdparm on Ubuntu 10.10.
root@ubu1010:~# aptitude install sdparm
...
root@ubu1010:~# sdparm /dev/sda | head -1
/dev/sda: ATA FUJITSU MJA2160B 0081
root@ubu1010:~# man sdparm
Use hdparm and sdparm with care.
45
disk devices
5.6. practice: hard disk devices
About this lab: To practice working with hard disks, you will need some hard disks. When
there are no physical hard disk available, you can use virtual disks in vmware or VirtualBox.
The teacher will help you in attaching a couple of ATA and/or SCSI disks to a virtual
machine. The results of this lab can be used in the next three labs (partitions, file systems,
mounting).
It is adviced to attach three 1GB disks and three 2GB disks to the virtual machine. This will
allow for some freedom in the practices of this chapter as well as the next chapters (raid,
lvm, iSCSI).
1. Use dmesg to make a list of hard disk devices detected at boot-up.
2. Use fdisk to find the total size of all hard disk devices on your system.
3. Stop a virtual machine, add three virtual 1 gigabyte scsi hard disk devices and one virtual
400 megabyte ide hard disk device. If possible, also add another virtual 400 megabyte ide
disk.
4. Use dmesg to verify that all the new disks are properly detected at boot-up.
5. Verify that you can see the disk devices in /dev.
6. Use fdisk (with grep and /dev/null) to display the total size of the new disks.
7. Use badblocks to completely erase one of the smaller hard disks.
8. Look at /proc/scsi/scsi.
9. If possible, install lsscsi, lshw and use them to list the disks.
46
disk devices
5.7. solution: hard disk devices
1. Use dmesg to make a list of hard disk devices detected at boot-up.
Some possible answers...
dmesg | grep -i disk
Looking for ATA disks: dmesg | grep hd[abcd]
Looking for ATA disks: dmesg | grep -i "ata disk"
Looking for SCSI disks: dmesg | grep sd[a-f]
Looking for SCSI disks: dmesg | grep -i "scsi disk"
2. Use fdisk to find the total size of all hard disk devices on your system.
fdisk -l
3. Stop a virtual machine, add three virtual 1 gigabyte scsi hard disk devices and one virtual
400 megabyte ide hard disk device. If possible, also add another virtual 400 megabyte ide
disk.
This exercise happens in the settings of vmware or VirtualBox.
4. Use dmesg to verify that all the new disks are properly detected at boot-up.
See 1.
5. Verify that you can see the disk devices in /dev.
SCSI+SATA: ls -l /dev/sd*
ATA: ls -l /dev/hd*
6. Use fdisk (with grep and /dev/null) to display the total size of the new disks.
root@rhel53 ~# fdisk -l 2>/dev/null | grep [MGT]B
Disk /dev/hda: 21.4 GB, 21474836480 bytes
Disk /dev/hdb: 1073 MB, 1073741824 bytes
Disk /dev/sda: 2147 MB, 2147483648 bytes
Disk /dev/sdb: 2147 MB, 2147483648 bytes
Disk /dev/sdc: 2147 MB, 2147483648 bytes
7. Use badblocks to completely erase one of the smaller hard disks.
#Verify the device (/dev/sdc??) you want to erase before typing this.
#
root@rhel53 ~# badblocks -ws /dev/sdc
Testing with pattern 0xaa: done
Reading and comparing: done
Testing with pattern 0x55: done
Reading and comparing: done
Testing with pattern 0xff: done
Reading and comparing: done
Testing with pattern 0x00: done
Reading and comparing: done
8. Look at /proc/scsi/scsi.
root@rhel53 ~# cat /proc/scsi/scsi
47
disk devices
Attached devices:
Host: scsi0 Channel: 00 Id: 02 Lun: 00
Vendor: VBOX Model: HARDDISK Rev: 1.0
Type: Direct-Access ANSI SCSI revision: 05
Host: scsi0 Channel: 00 Id: 03 Lun: 00
Vendor: VBOX Model: HARDDISK Rev: 1.0
Type: Direct-Access ANSI SCSI revision: 05
Host: scsi0 Channel: 00 Id: 06 Lun: 00
Vendor: VBOX Model: HARDDISK Rev: 1.0
Type: Direct-Access ANSI SCSI revision: 05
9. If possible, install lsscsi, lshw and use them to list the disks.
Debian,Ubuntu: aptitude install lsscsi lshw
Fedora: yum install lsscsi lshw
root@rhel53 ~# lsscsi
[0:0:2:0] disk VBOX HARDDISK 1.0 /dev/sda
[0:0:3:0] disk VBOX HARDDISK 1.0 /dev/sdb
[0:0:6:0] disk VBOX HARDDISK 1.0 /dev/sdc
48
Chapter 6. disk partitions
This chapter continues on the hard disk devices from the previous one. Here we will put
partitions on those devices.
This chapter prepares you for the next chapter, where we put file systems on our partitions.
49
disk partitions
6.1. about partitions
6.1.1. primary, extended and logical
Linux requires you to create one or more partitions. The next paragraphs will explain how
to create and use partitions.
A partition's geometry and size is usually defined by a starting and ending cylinder
(sometimes by sector). Partitions can be of type primary (maximum four), extended
(maximum one) or logical (contained within the extended partition). Each partition has a
type field that contains a code. This determines the computers operating system or the
partitions file system.
Table 6.1. primary, extended and logical partitions
Partition Type naming
Primary (max 4) 1-4
Extended (max 1) 1-4
Logical 5-
6.1.2. partition naming
We saw before that hard disk devices are named /dev/hdx or /dev/sdx with x depending on
the hardware configuration. Next is the partition number, starting the count at 1. Hence the
four (possible) primary partitions are numbered 1 to 4. Logical partition counting always
starts at 5. Thus /dev/hda2 is the second partition on the first ATA hard disk device, and /
dev/hdb5 is the first logical partition on the second ATA hard disk device. Same for SCSI, /
dev/sdb3 is the third partition on the second SCSI disk.
Table 6.2. Partition naming
partition device
/dev/hda1 first primary partition on /dev/hda
/dev/hda2 second primary or extended partition on /dev/hda
/dev/sda5 first logical drive on /dev/sda
/dev/sdb6 second logical on /dev/sdb
The picture below shows two (spindle) disks with partitions. Note that an extended partition
is a container holding logical drives.
50
disk partitions
6.2. discovering partitions
6.2.1. fdisk -l
In the fdisk -l example below you can see that two partitions exist on /dev/sdb. The first
partition spans 31 cylinders and contains a Linux swap partition. The second partition is
much bigger.
root@laika:~# fdisk -l /dev/sdb
Disk /dev/sdb: 100.0 GB, 100030242816 bytes
255 heads, 63 sectors/track, 12161 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdb1 1 31 248976 82 Linux swap / Solaris
/dev/sdb2 32 12161 97434225 83 Linux
root@laika:~#
6.2.2. /proc/partitions
The /proc/partitions file contains a table with major and minor number of partitioned
devices, their number of blocks and the device name in /dev. Verify with /proc/devices to
link the major number to the proper device.
paul@RHELv4u4:~$ cat /proc/partitions
major minor #blocks name
3 0 524288 hda
3 64 734003 hdb
8 0 8388608 sda
8 1 104391 sda1
8 2 8281507 sda2
8 16 1048576 sdb
8 32 1048576 sdc
8 48 1048576 sdd
253 0 7176192 dm-0
253 1 1048576 dm-1
The major number corresponds to the device type (or driver) and can be found in /proc/
devices. In this case 3 corresponds to ide and 8 to sd. The major number determines the
device driver to be used with this device.
The minor number is a unique identification of an instance of this device type. The
devices.txt file in the kernel tree contains a full list of major and minor numbers.
51
disk partitions
6.2.3. parted and others
You may be interested in alternatives to fdisk like parted, cfdisk, sfdisk and gparted. This
course mainly uses fdisk to partition hard disks.
parted is recommended by some Linux distributions for handling storage with gpt instead
of mbr.
Below a screenshot of parted on CentOS.
[root@centos65 ~]# rpm -q parted
parted-2.1-21.el6.x86_64
[root@centos65 ~]# parted /dev/sda
GNU Parted 2.1
Using /dev/sda
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted) print
Model: ATA VBOX HARDDISK (scsi)
Disk /dev/sda: 42.9GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Number Start End Size Type File system Flags
1 1049kB 525MB 524MB primary ext4 boot
2 525MB 42.9GB 42.4GB primary lvm
(parted)
52
disk partitions
6.3. partitioning new disks
In the example below, we bought a new disk for our system. After the new hardware is
properly attached, you can use fdisk and parted to create the necessary partition(s). This
example uses fdisk, but there is nothing wrong with using parted.
6.3.1. recognising the disk
First, we check with fdisk -l whether Linux can see the new disk. Yes it does, the new disk
is seen as /dev/sdb, but it does not have any partitions yet.
root@RHELv4u2:~# fdisk -l
Disk /dev/sda: 12.8 GB, 12884901888 bytes
255 heads, 63 sectors/track, 1566 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 * 1 13 104391 83 Linux
/dev/sda2 14 1566 12474472+ 8e Linux LVM
Disk /dev/sdb: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Disk /dev/sdb doesn't contain a valid partition table
6.3.2. opening the disk with fdisk
Then we create a partition with fdisk on /dev/sdb. First we start the fdisk tool with /dev/sdb
as argument. Be very very careful not to partition the wrong disk!!
root@RHELv4u2:~# fdisk /dev/sdb
Device contains neither a valid DOS partition table, nor Sun, SGI...
Building a new DOS disklabel. Changes will remain in memory only,
until you decide to write them. After that, of course, the previous
content won't be recoverable.
Warning: invalid flag 0x0000 of partition table 4 will be corrected...
6.3.3. empty partition table
Inside the fdisk tool, we can issue the p command to see the current disks partition table.
Command (m for help): p
Disk /dev/sdb: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
53
disk partitions
6.3.4. create a new partition
No partitions exist yet, so we issue n to create a new partition. We choose p for primary, 1
for the partition number, 1 for the start cylinder and 14 for the end cylinder.
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-130, default 1):
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-130, default 130): 14
We can now issue p again to verify our changes, but they are not yet written to disk. This
means we can still cancel this operation! But it looks good, so we use w to write the changes
to disk, and then quit the fdisk tool.
Command (m for help): p
Disk /dev/sdb: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdb1 1 14 112423+ 83 Linux
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
root@RHELv4u2:~#
6.3.5. display the new partition
Let's verify again with fdisk -l to make sure reality fits our dreams. Indeed, the screenshot
below now shows a partition on /dev/sdb.
root@RHELv4u2:~# fdisk -l
Disk /dev/sda: 12.8 GB, 12884901888 bytes
255 heads, 63 sectors/track, 1566 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 * 1 13 104391 83 Linux
/dev/sda2 14 1566 12474472+ 8e Linux LVM
Disk /dev/sdb: 1073 MB, 1073741824 bytes
255 heads, 63 sectors/track, 130 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sdb1 1 14 112423+ 83 Linux
root@RHELv4u2:~#
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disk partitions
6.4. about the partition table
6.4.1. master boot record
The partition table information (primary and extended partitions) is written in the master
boot record or mbr. You can use dd to copy the mbr to a file.
This example copies the master boot record from the first SCSI hard disk.
dd if=/dev/sda of=/SCSIdisk.mbr bs=512 count=1
The same tool can also be used to wipe out all information about partitions on a disk. This
example writes zeroes over the master boot record.
dd if=/dev/zero of=/dev/sda bs=512 count=1
Or to wipe out the whole partition or disk.
dd if=/dev/zero of=/dev/sda
6.4.2. partprobe
Don't forget that after restoring a master boot record with dd, that you need to force the
kernel to reread the partition table with partprobe. After running partprobe, the partitions
can be used again.
[root@RHEL5 ~]# partprobe
[root@RHEL5 ~]#
6.4.3. logical drives
The partition table does not contain information about logical drives. So the dd backup
of the mbr only works for primary and extended partitions. To backup the partition table
including the logical drives, you can use sfdisk.
This example shows how to backup all partition and logical drive information to a file.
sfdisk -d /dev/sda > parttable.sda.sfdisk
The following example copies the mbr and all logical drive info from /dev/sda to /dev/sdb.
sfdisk -d /dev/sda | sfdisk /dev/sdb
55
disk partitions
6.5. GUID partition table
gpt was developed because of the limitations of the 1980s mbr partitioning scheme (for
example only four partitions can be defined, and they have a maximum size two terabytes).
Since 2010 gpt is a part of the uefi specification, but it is also used on bios systems.
Newer versions of fdisk work fine with gpt, but most production servers today (mid 2015)
still have an older fdisk.. You can use parted instead.
6.6. labeling with parted
parted is an interactive tool, just like fdisk. Type help in parted for a list of commands
and options.
This screenshot shows how to start parted to manage partitions on /dev/sdb.
[root@rhel71 ~]# parted /dev/sdb
GNU Parted 3.1
Using /dev/sdb
Welcome to GNU Parted! Type 'help' to view a list of commands.
(parted)
Each command also has built-in help. For example help mklabel will list all supported
labels. Note that we only discussed mbr(msdos) and gpt in this book.
(parted) help mklabel
mklabel,mktable LABEL-TYPE create a new disklabel (partition table)
LABEL-TYPE is one of: aix, amiga, bsd, dvh, gpt, mac, msdos, pc98, sun, loop
(parted)
We create an mbr label.
(parted) mklabel msdos>
Warning: The existing disk label on /dev/sdb will be destroyed and all data on
this disk will be lost. Do you want to continue?
Yes/No? yes
(parted) mklabel gpt
Warning: The existing disk label on /dev/sdb will be destroyed and all data on
this disk will be lost. Do you want to continue?
Yes/No? Y
(parted)
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disk partitions
6.6.1. partitioning with parted
Once labeled it is easy to create partitions with parted. This screenshot starts with an
unpartitioned (but gpt labeled) disk.
(parted) print
Model: ATA VBOX HARDDISK (scsi)
Disk /dev/sdb: 8590MB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags:
Number Start End Size File system Name Flags
(parted)
This example shows how to create two primary partitions of equal size.
(parted) mkpart primary 0 50%
Warning: The resulting partition is not properly aligned for best performance.
Ignore/Cancel? I
(parted) mkpart primary 50% 100%
(parted)
Verify with print and exit with quit. Since parted works directly on the disk, there is no
need to w(rite) like in fdisk.
(parted) print
Model: ATA VBOX HARDDISK (scsi)
Disk /dev/sdb: 8590MB
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Disk Flags:
Number Start End Size File system Name Flags
1 17.4kB 4295MB 4295MB primary
2 4295MB 8589MB 4294MB primary
(parted) quit
Information: You may need to update /etc/fstab.
[root@rhel71 ~]#
57
disk partitions
6.7. practice: partitions
1. Use fdisk -l to display existing partitions and sizes.
2. Use df -h to display existing partitions and sizes.
3. Compare the output of fdisk and df.
4. Create a 200MB primary partition on a small disk.
5. Create a 400MB primary partition and two 300MB logical drives on a big disk.
6. Use df -h and fdisk -l to verify your work.
7. Compare the output again of fdisk and df. Do both commands display the new partitions ?
8. Create a backup with dd of the mbr that contains your 200MB primary partition.
9. Take a backup of the partition table containing your 400MB primary and 300MB logical
drives. Make sure the logical drives are in the backup.
10. (optional) Remove all your partitions with fdisk. Then restore your backups.
58
disk partitions
6.8. solution: partitions
1. Use fdisk -l to display existing partitions and sizes.
as root: # fdisk -l
2. Use df -h to display existing partitions and sizes.
df -h
3. Compare the output of fdisk and df.
Some partitions will be listed in both outputs (maybe /dev/sda1 or /dev/hda1).
4. Create a 200MB primary partition on a small disk.
Choose one of the disks you added (this example uses /dev/sdc).
root@rhel53 ~# fdisk /dev/sdc
...
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-261, default 1): 1
Last cylinder or +size or +sizeM or +sizeK (1-261, default 261): +200m
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
5. Create a 400MB primary partition and two 300MB logical drives on a big disk.
Choose one of the disks you added (this example uses /dev/sdb)
fdisk /dev/sdb
inside fdisk : n p 1 +400m enter --- n e 2 enter enter --- n l +300m (twice)
6. Use df -h and fdisk -l to verify your work.
fdisk -l ; df -h
7. Compare the output again of fdisk and df. Do both commands display the new partitions ?
The newly created partitions are visible with fdisk.
But they are not displayed by df.
8. Create a backup with dd of the mbr that contains your 200MB primary partition.
dd if=/dev/sdc of=bootsector.sdc.dd count=1 bs=512
9. Take a backup of the partition table containing your 400MB primary and 300MB logical
drives. Make sure the logical drives are in the backup.
sfdisk -d /dev/sdb > parttable.sdb.sfdisk
59
Chapter 7. file systems
When you are finished partitioning the hard disk, you can put a file system on each partition.
This chapter builds on the partitions from the previous chapter, and prepares you for the
next one where we will mount the filesystems.
60
file systems
7.1. about file systems
A file system is a way of organizing files on your partition. Besides file-based storage, file
systems usually include directories and access control, and contain meta information about
files like access times, modification times and file ownership.
The properties (length, character set, ...) of filenames are determined by the file system you
choose. Directories are usually implemented as files, you will have to learn how this is
implemented! Access control in file systems is tracked by user ownership (and group owner-
and membership) in combination with one or more access control lists.
7.1.1. man fs
The manual page about filesystems is accessed by typing man fs.
[root@rhel65 ~]# man fs
7.1.2. /proc/filesystems
The Linux kernel will inform you about currently loaded file system drivers in /proc/
filesystems.
root@rhel53 ~# cat /proc/filesystems | grep -v nodev
ext2
iso9660
ext3
7.1.3. /etc/filesystems
The /etc/filesystems file contains a list of autodetected filesystems (in case the mount
command is used without the -t option.
Help for this file is provided by man mount.
[root@rhel65 ~]# man mount
61
file systems
7.2. common file systems
7.2.1. ext2 and ext3
Once the most common Linux file systems is the ext2 (the second extended) file system. A
disadvantage is that file system checks on ext2 can take a long time.
ext2 was being replaced by ext3 on most Linux machines. They are essentially the same,
except for the journaling which is only present in ext3.
Journaling means that changes are first written to a journal on the disk. The journal is
flushed regularly, writing the changes in the file system. Journaling keeps the file system
in a consistent state, so you don't need a file system check after an unclean shutdown or
power failure.
7.2.2. creating ext2 and ext3
You can create these file systems with the /sbin/mkfs or /sbin/mke2fs commands. Use
mke2fs -j to create an ext3 file system.
You can convert an ext2 to ext3 with tune2fs -j. You can mount an ext3 file system as ext2,
but then you lose the journaling. Do not forget to run mkinitrd if you are booting from this
device.
7.2.3. ext4
The newest incarnation of the ext file system is named ext4 and is available in the Linux
kernel since 2008. ext4 supports larger files (up to 16 terabyte) and larger file systems than
ext3 (and many more features).
Development started by making ext3 fully capable for 64-bit. When it turned out the changes
were significant, the developers decided to name it ext4.
7.2.4. xfs
Redhat Enterprise Linux 7 will have XFS as the default file system. This is a highly scalable
high-performance file system.
xfs was created for Irix and for a couple of years it was also used in FreeBSD. It is supported
by the Linux kernel, but rarely used in dsitributions outside of the Redhat/CentOS realm.
62
file systems
7.2.5. vfat
The vfat file system exists in a couple of forms : fat12 for floppy disks, fat16 on ms-dos, and
fat32 for larger disks. The Linux vfat implementation supports all of these, but vfat lacks a
lot of features like security and links. fat disks can be read by every operating system, and
are used a lot for digital cameras, usb sticks and to exchange data between different OS'ses
on a home user's computer.
7.2.6. iso 9660
iso 9660 is the standard format for cdroms. Chances are you will encounter this file system
also on your hard disk in the form of images of cdroms (often with the .iso extension). The
iso 9660 standard limits filenames to the 8.3 format. The Unix world didn't like this, and thus
added the rock ridge extensions, which allows for filenames up to 255 characters and Unix-
style file-modes, ownership and symbolic links. Another extensions to iso 9660 is joliet,
which adds 64 unicode characters to the filename. The el torito standard extends iso 9660
to be able to boot from CD-ROM's.
7.2.7. udf
Most optical media today (including cd's and dvd's) use udf, the Universal Disk Format.
7.2.8. swap
All things considered, swap is not a file system. But to use a partition as a swap partition
it must be formatted and mounted as swap space.
7.2.9. gfs
Linux clusters often use a dedicated cluster filesystem like GFS, GFS2, ClusterFS, ...
7.2.10. and more...
You may encounter reiserfs on older Linux systems. Maybe you will see Sun's zfs or the
open source btrfs. This last one requires a chapter on itself.
63
file systems
7.2.11. /proc/filesystems
The /proc/filesystems file displays a list of supported file systems. When you mount a file
system without explicitly defining one, then mount will first try to probe /etc/filesystems
and then probe /proc/filesystems for all the filesystems without the nodev label. If /etc/
filesystems ends with a line containing only an asterisk (*) then both files are probed.
paul@RHELv4u4:~$ cat /proc/filesystems
nodev sysfs
nodev rootfs
nodev bdev
nodev proc
nodev sockfs
nodev binfmt_misc
nodev usbfs
nodev usbdevfs
nodev futexfs
nodev tmpfs
nodev pipefs
nodev eventpollfs
nodev devpts
ext2
nodev ramfs
nodev hugetlbfs
iso9660
nodev relayfs
nodev mqueue
nodev selinuxfs
ext3
nodev rpc_pipefs
nodev vmware-hgfs
nodev autofs
paul@RHELv4u4:~$
64
file systems
7.3. putting a file system on a partition
We now have a fresh partition. The system binaries to make file systems can be found with ls.
[root@RHEL4b ~]# ls -lS /sbin/mk*
-rwxr-xr-x 3 root root 34832 Apr 24 2006 /sbin/mke2fs
-rwxr-xr-x 3 root root 34832 Apr 24 2006 /sbin/mkfs.ext2
-rwxr-xr-x 3 root root 34832 Apr 24 2006 /sbin/mkfs.ext3
-rwxr-xr-x 3 root root 28484 Oct 13 2004 /sbin/mkdosfs
-rwxr-xr-x 3 root root 28484 Oct 13 2004 /sbin/mkfs.msdos
-rwxr-xr-x 3 root root 28484 Oct 13 2004 /sbin/mkfs.vfat
-rwxr-xr-x 1 root root 20313 Apr 10 2006 /sbin/mkinitrd
-rwxr-x--- 1 root root 15444 Oct 5 2004 /sbin/mkzonedb
-rwxr-xr-x 1 root root 15300 May 24 2006 /sbin/mkfs.cramfs
-rwxr-xr-x 1 root root 13036 May 24 2006 /sbin/mkswap
-rwxr-xr-x 1 root root 6912 May 24 2006 /sbin/mkfs
-rwxr-xr-x 1 root root 5905 Aug 3 2004 /sbin/mkbootdisk
[root@RHEL4b ~]#
It is time for you to read the manual pages of mkfs and mke2fs. In the example below,
you see the creation of an ext2 file system on /dev/sdb1. In real life, you might want to use
options like -m0 and -j.
root@RHELv4u2:~# mke2fs /dev/sdb1
mke2fs 1.35 (28-Feb-2004)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
28112 inodes, 112420 blocks
5621 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67371008
14 block groups
8192 blocks per group, 8192 fragments per group
2008 inodes per group
Superblock backups stored on blocks:
8193, 24577, 40961, 57345, 73729
Writing inode tables: done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 37 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.
65
file systems
7.4. tuning a file system
You can use tune2fs to list and set file system settings. The first screenshot lists the reserved
space for root (which is set at five percent).
[root@rhel4 ~]# tune2fs -l /dev/sda1 | grep -i "block count"
Block count: 104388
Reserved block count: 5219
[root@rhel4 ~]#
This example changes this value to ten percent. You can use tune2fs while the file system
is active, even if it is the root file system (as in this example).
[root@rhel4 ~]# tune2fs -m10 /dev/sda1
tune2fs 1.35 (28-Feb-2004)
Setting reserved blocks percentage to 10 (10430 blocks)
[root@rhel4 ~]# tune2fs -l /dev/sda1 | grep -i "block count"
Block count: 104388
Reserved block count: 10430
[root@rhel4 ~]#
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file systems
7.5. checking a file system
The fsck command is a front end tool used to check a file system for errors.
[root@RHEL4b ~]# ls /sbin/*fsck*
/sbin/dosfsck /sbin/fsck /sbin/fsck.ext2 /sbin/fsck.msdos
/sbin/e2fsck /sbin/fsck.cramfs /sbin/fsck.ext3 /sbin/fsck.vfat
[root@RHEL4b ~]#
The last column in /etc/fstab is used to determine whether a file system should be checked
at boot-up.
[paul@RHEL4b ~]$ grep ext /etc/fstab
/dev/VolGroup00/LogVol00 / ext3 defaults 1 1
LABEL=/boot /boot ext3 defaults 1 2
[paul@RHEL4b ~]$
Manually checking a mounted file system results in a warning from fsck.
[root@RHEL4b ~]# fsck /boot
fsck 1.35 (28-Feb-2004)
e2fsck 1.35 (28-Feb-2004)
/dev/sda1 is mounted.
WARNING!!! Running e2fsck on a mounted filesystem may cause
SEVERE filesystem damage.
Do you really want to continue (y/n)? no
check aborted.
But after unmounting fsck and e2fsck can be used to check an ext2 file system.
[root@RHEL4b ~]# fsck /boot
fsck 1.35 (28-Feb-2004)
e2fsck 1.35 (28-Feb-2004)
/boot: clean, 44/26104 files, 17598/104388 blocks
[root@RHEL4b ~]# fsck -p /boot
fsck 1.35 (28-Feb-2004)
/boot: clean, 44/26104 files, 17598/104388 blocks
[root@RHEL4b ~]# e2fsck -p /dev/sda1
/boot: clean, 44/26104 files, 17598/104388 blocks
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file systems
7.6. practice: file systems
1. List the filesystems that are known by your system.
2. Create an ext2 filesystem on the 200MB partition.
3. Create an ext3 filesystem on one of the 300MB logical drives.
4. Create an ext4 on the 400MB partition.
5. Set the reserved space for root on the ext3 filesystem to 0 percent.
6. Verify your work with fdisk and df.
7. Perform a file system check on all the new file systems.
68
file systems
7.7. solution: file systems
1. List the filesystems that are known by your system.
man fs
cat /proc/filesystems
cat /etc/filesystems (not on all Linux distributions)
2. Create an ext2 filesystem on the 200MB partition.
mke2fs /dev/sdc1 (replace sdc1 with the correct partition)
3. Create an ext3 filesystem on one of the 300MB logical drives.
mke2fs -j /dev/sdb5 (replace sdb5 with the correct partition)
4. Create an ext4 on the 400MB partition.
mkfs.ext4 /dev/sdb1 (replace sdb1 with the correct partition)
5. Set the reserved space for root on the ext3 filesystem to 0 percent.
tune2fs -m 0 /dev/sdb5
6. Verify your work with fdisk and df.
mkfs (mke2fs) makes no difference in the output of these commands
The big change is in the next topic: mounting
7. Perform a file system check on all the new file systems.
fsck /dev/sdb1
fsck /dev/sdc1
fsck /dev/sdb5
69
Chapter 8. mounting
Once you've put a file system on a partition, you can mount it. Mounting a file system
makes it available for use, usually as a directory. We say mounting a file system instead
of mounting a partition because we will see later that we can also mount file systems that
do not exists on partitions.
On all Unix systems, every file and every directory is part of one big file tree. To access
a file, you need to know the full path starting from the root directory. When adding a file
system to your computer, you need to make it available somewhere in the file tree. The
directory where you make a file system available is called a mount point.
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8.1. mounting local file systems
8.1.1. mkdir
This example shows how to create a new mount point with mkdir.
root@RHELv4u2:~# mkdir /home/project42
8.1.2. mount
When the mount point is created, and a file system is present on the partition, then mount
can mount the file system on the mount point directory.
root@RHELv4u2:~# mount -t ext2 /dev/sdb1 /home/project42/
Once mounted, the new file system is accessible to users.
8.1.3. /etc/filesystems
Actually the explicit -t ext2 option to set the file system is not always necessary. The mount
command is able to automatically detect a lot of file systems.
When mounting a file system without specifying explicitly the file system, then mount will
first probe /etc/filesystems. Mount will skip lines with the nodev directive.
paul@RHELv4u4:~$ cat /etc/filesystems
ext3
ext2
nodev proc
nodev devpts
iso9660
vfat
hfs
8.1.4. /proc/filesystems
When /etc/filesystems does not exist, or ends with a single * on the last line, then mount
will read /proc/filesystems.
[root@RHEL52 ~]# cat /proc/filesystems | grep -v ^nodev
ext2
iso9660
ext3
8.1.5. umount
You can unmount a mounted file system using the umount command.
root@pasha:~# umount /home/reet
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8.2. displaying mounted file systems
To display all mounted file systems, issue the mount command. Or look at the files /proc/
mounts and /etc/mtab.
8.2.1. mount
The simplest and most common way to view all mounts is by issuing the mount command
without any arguments.
root@RHELv4u2:~# mount | grep /dev/sdb
/dev/sdb1 on /home/project42 type ext2 (rw)
8.2.2. /proc/mounts
The kernel provides the info in /proc/mounts in file form, but /proc/mounts does not exist
as a file on any hard disk. Looking at /proc/mounts is looking at information that comes
directly from the kernel.
root@RHELv4u2:~# cat /proc/mounts | grep /dev/sdb
/dev/sdb1 /home/project42 ext2 rw 0 0
8.2.3. /etc/mtab
The /etc/mtab file is not updated by the kernel, but is maintained by the mount command.
Do not edit /etc/mtab manually.
root@RHELv4u2:~# cat /etc/mtab | grep /dev/sdb
/dev/sdb1 /home/project42 ext2 rw 0 0
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8.2.4. df
A more user friendly way to look at mounted file systems is df. The df (diskfree) command
has the added benefit of showing you the free space on each mounted disk. Like a lot of
Linux commands, df supports the -h switch to make the output more human readable.
root@RHELv4u2:~# df
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
11707972 6366996 4746240 58% /
/dev/sda1 101086 9300 86567 10% /boot
none 127988 0 127988 0% /dev/shm
/dev/sdb1 108865 1550 101694 2% /home/project42
root@RHELv4u2:~# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup00-LogVol00
12G 6.1G 4.6G 58% /
/dev/sda1 99M 9.1M 85M 10% /boot
none 125M 0 125M 0% /dev/shm
/dev/sdb1 107M 1.6M 100M 2% /home/project42
8.2.5. df -h
In the df -h example below you can see the size, free space, used gigabytes and percentage
and mount point of a partition.
root@laika:~# df -h | egrep -e "(sdb2|File)"
Filesystem Size Used Avail Use% Mounted on
/dev/sdb2 92G 83G 8.6G 91% /media/sdb2
8.2.6. du
The du command can summarize disk usage for files and directories. By using du on a
mount point you effectively get the disk space used on a file system.
While du can go display each subdirectory recursively, the -s option will give you a total
summary for the parent directory. This option is often used together with -h. This means du
-sh on a mount point gives the total amount used by the file system in that partition.
root@debian6~# du -sh /boot /srv/wolf
6.2M /boot
1.1T /srv/wolf
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8.3. from start to finish
Below is a screenshot that show a summary roadmap starting with detection of the hardware
(/dev/sdb) up until mounting on /mnt.
[root@centos65 ~]# dmesg | grep '\[sdb\]'
sd 3:0:0:0: [sdb] 150994944 512-byte logical blocks: (77.3 GB/72.0 GiB)
sd 3:0:0:0: [sdb] Write Protect is off
sd 3:0:0:0: [sdb] Mode Sense: 00 3a 00 00
sd 3:0:0:0: [sdb] Write cache: enabled, read cache: enabled, doesn't support \
DPO or FUA
sd 3:0:0:0: [sdb] Attached SCSI disk
[root@centos65 ~]# parted /dev/sdb
(parted) mklabel msdos
(parted) mkpart primary ext4 1 77000
(parted) print
Model: ATA VBOX HARDDISK (scsi)
Disk /dev/sdb: 77.3GB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Number Start End Size Type File system Flags
1 1049kB 77.0GB 77.0GB primary
(parted) quit
[root@centos65 ~]# mkfs.ext4 /dev/sdb1
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
4702208 inodes, 18798592 blocks
939929 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=4294967296
574 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
( output truncated )
...
[root@centos65 ~]# mount /dev/sdb1 /mnt
[root@centos65 ~]# mount | grep mnt
/dev/sdb1 on /mnt type ext4 (rw)
[root@centos65 ~]# df -h | grep mnt
/dev/sdb1 71G 180M 67G 1% /mnt
[root@centos65 ~]# du -sh /mnt
20K /mnt
[root@centos65 ~]# umount /mnt
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8.4. permanent mounts
Until now, we performed all mounts manually. This works nice, until the next reboot.
Luckily there is a way to tell your computer to automatically mount certain file systems
during boot.
8.4.1. /etc/fstab
The file system table located in /etc/fstab contains a list of file systems, with an option to
automtically mount each of them at boot time.
Below is a sample /etc/fstab file.
root@RHELv4u2:~# cat /etc/fstab
/dev/VolGroup00/LogVol00 / ext3 defaults 1 1
LABEL=/boot /boot ext3 defaults 1 2
none /dev/pts devpts gid=5,mode=620 0 0
none /dev/shm tmpfs defaults 0 0
none /proc proc defaults 0 0
none /sys sysfs defaults 0 0
/dev/VolGroup00/LogVol01 swap swap defaults 0 0
By adding the following line, we can automate the mounting of a file system.
/dev/sdb1 /home/project42 ext2 defaults 0 0
8.4.2. mount /mountpoint
Adding an entry to /etc/fstab has the added advantage that you can simplify the mount
command. The command in the screenshot below forces mount to look for the partition
info in /etc/fstab.
root@rhel65:~# mount /home/project42
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8.5. securing mounts
File systems can be secured with several mount options. Here are some examples.
8.5.1. ro
The ro option will mount a file system as read only, preventing anyone from writing.
root@rhel53 ~# mount -t ext2 -o ro /dev/hdb1 /home/project42
root@rhel53 ~# touch /home/project42/testwrite
touch: cannot touch `/home/project42/testwrite': Read-only file system
8.5.2. noexec
The noexec option will prevent the execution of binaries and scripts on the mounted file
system.
root@rhel53 ~# mount -t ext2 -o noexec /dev/hdb1 /home/project42
root@rhel53 ~# cp /bin/cat /home/project42
root@rhel53 ~# /home/project42/cat /etc/hosts
-bash: /home/project42/cat: Permission denied
root@rhel53 ~# echo echo hello > /home/project42/helloscript
root@rhel53 ~# chmod +x /home/project42/helloscript
root@rhel53 ~# /home/project42/helloscript
-bash: /home/project42/helloscript: Permission denied
8.5.3. nosuid
The nosuid option will ignore setuid bit set binaries on the mounted file system.
Note that you can still set the setuid bit on files.
root@rhel53 ~# mount -o nosuid /dev/hdb1 /home/project42
root@rhel53 ~# cp /bin/sleep /home/project42/
root@rhel53 ~# chmod 4555 /home/project42/sleep
root@rhel53 ~# ls -l /home/project42/sleep
-r-sr-xr-x 1 root root 19564 Jun 24 17:57 /home/project42/sleep
But users cannot exploit the setuid feature.
root@rhel53 ~# su - paul
[paul@rhel53 ~]$ /home/project42/sleep 500 &
[1] 2876
[paul@rhel53 ~]$ ps -f 2876
UID PID PPID C STIME TTY STAT TIME CMD
paul 2876 2853 0 17:58 pts/0 S 0:00 /home/project42/sleep 500
[paul@rhel53 ~]$
8.5.4. noacl
To prevent cluttering permissions with acl's, use the noacl option.
root@rhel53 ~# mount -o noacl /dev/hdb1 /home/project42
More mount options can be found in the manual page of mount.
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8.6. mounting remote file systems
8.6.1. smb/cifs
The Samba team (samba.org) has a Unix/Linux service that is compatible with the SMB/
CIFS protocol. This protocol is mainly used by networked Microsoft Windows computers.
Connecting to a Samba server (or to a Microsoft computer) is also done with the mount
command.
This example shows how to connect to the 10.0.0.42 server, to a share named data2.
[root@centos65 ~]# mount -t cifs -o user=paul //10.0.0.42/data2 /home/data2
Password:
[root@centos65 ~]# mount | grep cifs
//10.0.0.42/data2 on /home/data2 type cifs (rw)
The above requires yum install cifs-client.
8.6.2. nfs
Unix servers often use nfs (aka the network file system) to share directories over the network.
Setting up an nfs server is discussed later. Connecting as a client to an nfs server is done
with mount, and is very similar to connecting to local storage.
This command shows how to connect to the nfs server named server42, which is sharing
the directory /srv/data. The mount point at the end of the command (/home/data) must
already exist.
[root@centos65 ~]# mount -t nfs server42:/srv/data /home/data
[root@centos65 ~]#
If this server42 has ip-address 10.0.0.42 then you can also write:
[root@centos65 ~]# mount -t nfs 10.0.0.42:/srv/data /home/data
[root@centos65 ~]# mount | grep data
10.0.0.42:/srv/data on /home/data type nfs (rw,vers=4,addr=10.0.0.42,clienta\
ddr=10.0.0.33)
8.6.3. nfs specific mount options
bg If mount fails, retry in background.
fg (default)If mount fails, retry in foreground.
soft Stop trying to mount after X attempts.
hard (default)Continue trying to mount.
The soft+bg options combined guarantee the fastest client boot if there are NFS problems.
retrans=X Try X times to connect (over udp).
tcp Force tcp (default and supported)
udp Force udp (unsupported)
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8.7. practice: mounting file systems
1. Mount the small 200MB partition on /home/project22.
2. Mount the big 400MB primary partition on /mnt, the copy some files to it (everything in /
etc). Then umount, and mount the file system as read only on /srv/nfs/salesnumbers. Where
are the files you copied ?
3. Verify your work with fdisk, df and mount. Also look in /etc/mtab and /proc/mounts.
4. Make both mounts permanent, test that it works.
5. What happens when you mount a file system on a directory that contains some files ?
6. What happens when you mount two file systems on the same mount point ?
7. (optional) Describe the difference between these commands: find, locate, updatedb,
makewhatis, whereis, apropos, which and type.
8. (optional) Perform a file system check on the partition mounted at /srv/nfs/salesnumbers.
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8.8. solution: mounting file systems
1. Mount the small 200MB partition on /home/project22.
mkdir /home/project22
mount /dev/sdc1 /home/project22
2. Mount the big 400MB primary partition on /mnt, the copy some files to it (everything in /
etc). Then umount, and mount the file system as read only on /srv/nfs/salesnumbers. Where
are the files you copied ?
mount /dev/sdb1 /mnt
cp -r /etc /mnt
ls -l /mnt
umount /mnt
ls -l /mnt
mkdir -p /srv/nfs/salesnumbers
mount /dev/sdb1 /srv/nfs/salesnumbers
You see the files in /srv/nfs/salenumbers now...
But physically they are on ext3 on partition /dev/sdb1
3. Verify your work with fdisk, df and mount. Also look in /etc/mtab and /proc/mounts.
fdisk -l
df -h
mount
All three the above commands should show your mounted partitions.
grep project22 /etc/mtab
grep project22 /proc/mounts
4. Make both mounts permanent, test that it works.
add the following lines to /etc/fstab
/dev/sdc1 /home/project22 auto defaults 0 0
/dev/sdb1 /srv/nfs/salesnumbers auto defaults 0 0
5. What happens when you mount a file system on a directory that contains some files ?
The files are hidden until umount.
6. What happens when you mount two file systems on the same mount point ?
Only the last mounted fs is visible.
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7. (optional) Describe the difference between these commands: find, locate, updatedb,
makewhatis, whereis, apropos, which and type.
man find
man locate
...
8. (optional) Perform a file system check on the partition mounted at /srv/nfs/salesnumbers.
# umount /srv/nfs/salesnumbers (optional but recommended)
# fsck /dev/sdb1
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Chapter 9. troubleshooting tools
This chapter introduces some tools that go beyond df -h and du -sh. Tools that will enable
you to troubleshoot a variety of issues with file systems and storage.
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9.1. lsof
List open files with lsof.
When invoked without options, lsof will list all open files. You can see the command (init in
this case), its PID (1) and the user (root) has openend the root directory and /sbin/init. The
FD (file descriptor) columns shows that / is both the root directory (rtd) and current working
directory (cwd) for the /sbin/init command. The FD column displays rtd for root directory,
cwd for current directory and txt for text (both including data and code).
root@debian7:~# lsof | head -4
COMMAND PID TID USER FD TYPE DEVICE SIZE/OFF NODE NAME
init 1 root cwd DIR 254,0 4096 2 /
init 1 root rtd DIR 254,0 4096 2 /
init 1 root txt REG 254,0 36992 130856 /sbin/init
Other options in the FD column besides w for writing, are r for reading and u for both reading
and writing. You can look at open files for a process id by typing lsof -p PID. For init this
would look like this:
lsof -p 1
The screenshot below shows basic use of lsof to prove that vi keeps a .swp file open (even
when stopped in background) on our freshly mounted file system.
[root@RHEL65 ~]# df -h | grep sdb
/dev/sdb1 541M 17M 497M 4% /srv/project33
[root@RHEL65 ~]# vi /srv/project33/busyfile.txt
[1]+ Stopped vi /srv/project33/busyfile.txt
[root@RHEL65 ~]# lsof /srv/*
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
vi 3243 root 3u REG 8,17 4096 12 /srv/project33/.busyfile.txt.swp
Here we see that rsyslog has a couple of log files open for writing (the FD column).
root@debian7:~# lsof /var/log/*
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
rsyslogd 2013 root 1w REG 254,0 454297 1308187 /var/log/syslog
rsyslogd 2013 root 2w REG 254,0 419328 1308189 /var/log/kern.log
rsyslogd 2013 root 5w REG 254,0 116725 1308200 /var/log/debug
rsyslogd 2013 root 6w REG 254,0 309847 1308201 /var/log/messages
rsyslogd 2013 root 7w REG 254,0 17591 1308188 /var/log/daemon.log
rsyslogd 2013 root 8w REG 254,0 101768 1308186 /var/log/auth.log
You can specify a specific user with lsof -u. This example shows the current working
directory for a couple of command line programs.
[paul@RHEL65 ~]$ lsof -u paul | grep home
bash 3302 paul cwd DIR 253,0 4096 788024 /home/paul
lsof 3329 paul cwd DIR 253,0 4096 788024 /home/paul
grep 3330 paul cwd DIR 253,0 4096 788024 /home/paul
lsof 3331 paul cwd DIR 253,0 4096 788024 /home/paul
The -u switch of lsof also supports the ^ character meaning 'not'. To see all open files, but
not those open by root:
lsof -u^root
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9.2. fuser
The fuser command will display the 'user' of a file system.
In this example we still have a vi process in background and we use fuser to find the process
id of the process using this file system.
[root@RHEL65 ~]# jobs
[1]+ Stopped vi /srv/project33/busyfile.txt
[root@RHEL65 ~]# fuser -m /srv/project33/
/srv/project33/: 3243
Adding the -u switch will also display the user name.
[root@RHEL65 ~]# fuser -m -u /srv/project33/
/srv/project33/: 3243(root)
You can quickly kill all processes that are using a specific file (or directory) with the -k
switch.
[root@RHEL65 ~]# fuser -m -k -u /srv/project33/
/srv/project33/: 3243(root)
[1]+ Killed vi /srv/project33/busyfile.txt
[root@RHEL65 ~]# fuser -m -u /srv/project33/
[root@RHEL65 ~]#
This example shows all processes that are using the current directory (bash and vi in this
case).
root@debian7:~/test42# vi file42
[1]+ Stopped vi file42
root@debian7:~/test42# fuser -v .
USER PID ACCESS COMMAND
/root/test42: root 2909 ..c.. bash
root 3113 ..c.. vi
This example shows that the vi command actually accesses /usr/bin/vim.basic as an
executable file.
root@debian7:~/test42# fuser -v $(which vi)
USER PID ACCESS COMMAND
/usr/bin/vim.basic: root 3113 ...e. vi
The last example shows how to find the process that is accessing a specific file.
[root@RHEL65 ~]# vi /srv/project33/busyfile.txt
[1]+ Stopped vi /srv/project33/busyfile.txt
[root@RHEL65 ~]# fuser -v -m /srv/project33/busyfile.txt
USER PID ACCESS COMMAND
/srv/project33/busyfile.txt:
root 13938 F.... vi
[root@RHEL65 ~]# ps -fp 13938
UID PID PPID C STIME TTY TIME CMD
root 13938 3110 0 15:47 pts/0 00:00:00 vi /srv/project33/busyfile.txt
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9.3. chroot
The chroot command creates a shell with an alternate root directory. It effectively hides
anything outside of this directory.
In the example below we assume that our system refuses to start (maybe because there is a
problem with /etc/fstab or the mounting of the root file system).
We start a live system (booted from cd/dvd/usb) to troubleshoot our server. The live system
will not use our main hard disk as root device
root@livecd:~# df -h | grep root
rootfs 186M 11M 175M 6% /
/dev/loop0 807M 807M 0 100% /lib/live/mount/rootfs/filesystem.squashfs
root@livecd:~# mount | grep root
/dev/loop0 on /lib/live/mount/rootfs/filesystem.squashfs type squashfs (ro)
We create some test file on the current rootfs.
root@livecd:~# touch /file42
root@livecd:~# mkdir /dir42
root@livecd:~# ls /
bin dir42 home lib64 opt run srv usr
boot etc initrd.img media proc sbin sys var
dev file42 lib mnt root selinux tmp vmlinuz
First we mount the root file system from the disk (which is on lvm so we use /dev/mapper
instead of /dev/sda5).
root@livecd:~# mount /dev/mapper/packer--debian--7-root /mnt
We are now ready to chroot into the rootfs on disk.
root@livecd:~# cd /mnt
root@livecd:/mnt# chroot /mnt
root@livecd:/# ls /
bin dev initrd.img lost+found opt run srv usr vmlinuz
boot etc lib media proc sbin sys vagrant
data home lib64 mnt root selinux tmp var
Our test files (file42 and dir42) are not visible because they are out of the chrooted
environment.
Note that the hostname of the chrooted environment is identical to the existing hostname.
To exit the chrooted file system:
root@livecd:/# exit
exit
root@livecd:~# ls /
bin dir42 home lib64 opt run srv usr
boot etc initrd.img media proc sbin sys var
dev file42 lib mnt root selinux tmp vmlinuz
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9.4. iostat
iostat reports IO statitics every given period of time. It also includes a small cpu usage
summary. This example shows iostat running every ten seconds with /dev/sdc and /dev/sde
showing a lot of write activity.
[root@RHEL65 ~]# iostat 10 3
Linux 2.6.32-431.el6.x86_64 (RHEL65) 06/16/2014 _x86_64_ (1 CPU)
avg-cpu: %user %nice %system %iowait %steal %idle
5.81 0.00 3.15 0.18 0.00 90.85
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sda 42.08 1204.10 1634.88 1743708 2367530
sdb 1.20 7.69 45.78 11134 66292
sdc 0.92 5.30 45.82 7672 66348
sdd 0.91 5.29 45.78 7656 66292
sde 1.04 6.28 91.49 9100 132496
sdf 0.70 3.40 91.46 4918 132440
sdg 0.69 3.40 91.46 4918 132440
dm-0 191.68 1045.78 1362.30 1514434 1972808
dm-1 49.26 150.54 243.55 218000 352696
avg-cpu: %user %nice %system %iowait %steal %idle
56.11 0.00 16.83 0.10 0.00 26.95
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sda 257.01 10185.97 76.95 101656 768
sdb 0.00 0.00 0.00 0 0
sdc 3.81 1.60 2953.11 16 29472
sdd 0.00 0.00 0.00 0 0
sde 4.91 1.60 4813.63 16 48040
sdf 0.00 0.00 0.00 0 0
sdg 0.00 0.00 0.00 0 0
dm-0 283.77 10185.97 76.95 101656 768
dm-1 0.00 0.00 0.00 0 0
avg-cpu: %user %nice %system %iowait %steal %idle
67.65 0.00 31.11 0.11 0.00 1.13
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sda 466.86 26961.09 178.28 238336 1576
sdb 0.00 0.00 0.00 0 0
sdc 31.45 0.90 24997.29 8 220976
sdd 0.00 0.00 0.00 0 0
sde 0.34 0.00 5.43 0 48
sdf 0.00 0.00 0.00 0 0
sdg 0.00 0.00 0.00 0 0
dm-0 503.62 26938.46 178.28 238136 1576
dm-1 2.83 22.62 0.00 200 0
[root@RHEL65 ~]#
Other options are to specify the disks you want to monitor (every 5 seconds here):
iostat sdd sde sdf 5
Or to show statistics per partition:
iostat -p sde -p sdf 5
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9.5. iotop
iotop works like the top command but orders processes by input/output instead of by CPU.
By default iotop will show all processes. This example uses iotop -o to only display
processes with actual I/O.
[root@RHEL65 ~]# iotop -o
Total DISK READ: 8.63 M/s | Total DISK WRITE: 0.00 B/s
TID PRIO USER DISK READ DISK WRITE SWAPIN IO> COMMAND
15000 be/4 root 2.43 M/s 0.00 B/s 0.00 % 14.60 % tar cjf /srv/di...
25000 be/4 root 6.20 M/s 0.00 B/s 0.00 % 6.15 % tar czf /srv/di...
24988 be/4 root 0.00 B/s 7.21 M/s 0.00 % 0.00 % gzip
25003 be/4 root 0.00 B/s 1591.19 K/s 0.00 % 0.00 % gzip
25004 be/4 root 0.00 B/s 193.51 K/s 0.00 % 0.00 % bzip2
Use the -b switch to create a log of iotop output (instead of the default interactive view).
[root@RHEL65 ~]# iotop -bod 10
Total DISK READ: 12.82 M/s | Total DISK WRITE: 5.69 M/s
TID PRIO USER DISK READ DISK WRITE SWAPIN IO COMMAND
25153 be/4 root 2.05 M/s 0.00 B/s 0.00 % 7.81 % tar cjf /srv/di...
25152 be/4 root 10.77 M/s 0.00 B/s 0.00 % 2.94 % tar czf /srv/di...
25144 be/4 root 408.54 B/s 0.00 B/s 0.00 % 0.05 % python /usr/sbi...
12516 be/3 root 0.00 B/s 1491.33 K/s 0.00 % 0.04 % [jbd2/sdc1-8]
12522 be/3 root 0.00 B/s 45.48 K/s 0.00 % 0.01 % [jbd2/sde1-8]
25158 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [flush-8:64]
25155 be/4 root 0.00 B/s 493.12 K/s 0.00 % 0.00 % bzip2
25156 be/4 root 0.00 B/s 2.81 M/s 0.00 % 0.00 % gzip
25159 be/4 root 0.00 B/s 528.63 K/s 0.00 % 0.00 % [flush-8:32]
This is an example of iotop to track disk I/O every ten seconds for one user named vagrant
(and only one process of this user, but this can be omitted). The -a switch accumulates I/
O over time.
[root@RHEL65 ~]# iotop -q -a -u vagrant -b -p 5216 -d 10 -n 10
Total DISK READ: 0.00 B/s | Total DISK WRITE: 0.00 B/s
TID PRIO USER DISK READ DISK WRITE SWAPIN IO COMMAND
5216 be/4 vagrant 0.00 B 0.00 B 0.00 % 0.00 % gzip
Total DISK READ: 818.22 B/s | Total DISK WRITE: 20.78 M/s
5216 be/4 vagrant 0.00 B 213.89 M 0.00 % 0.00 % gzip
Total DISK READ: 2045.95 B/s | Total DISK WRITE: 23.16 M/s
5216 be/4 vagrant 0.00 B 430.70 M 0.00 % 0.00 % gzip
Total DISK READ: 1227.50 B/s | Total DISK WRITE: 22.37 M/s
5216 be/4 vagrant 0.00 B 642.02 M 0.00 % 0.00 % gzip
Total DISK READ: 818.35 B/s | Total DISK WRITE: 16.44 M/s
5216 be/4 vagrant 0.00 B 834.09 M 0.00 % 0.00 % gzip
Total DISK READ: 6.95 M/s | Total DISK WRITE: 8.74 M/s
5216 be/4 vagrant 0.00 B 920.69 M 0.00 % 0.00 % gzip
Total DISK READ: 21.71 M/s | Total DISK WRITE: 11.99 M/s
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troubleshooting tools
9.6. vmstat
While vmstat is mainly a memory monitoring tool, it is worth mentioning here for its
reporting on summary I/O data for block devices and swap space.
This example shows some disk activity (underneath the -----io---- column), without
swapping.
[root@RHEL65 ~]# vmstat 5 10
procs ----------memory---------- ---swap-- -----io---- --system-- -----cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
0 0 5420 9092 14020 340876 7 12 235 252 77 100 2 1 98 0 0
2 0 5420 6104 13840 338176 0 0 7401 7812 747 1887 38 12 50 0 0
2 0 5420 10136 13696 336012 0 0 11334 14 1725 4036 76 24 0 0 0
0 0 5420 14160 13404 341552 0 0 10161 9914 1174 1924 67 15 18 0 0
0 0 5420 14300 13420 341564 0 0 0 16 28 18 0 0 100 0 0
0 0 5420 14300 13420 341564 0 0 0 0 22 16 0 0 100 0 0
...
[root@RHEL65 ~]#
You can benefit from vmstat's ability to display memory in kilobytes, megabytes or even
kibibytes and mebibytes using -S (followed by k K m or M).
[root@RHEL65 ~]# vmstat -SM 5 10
procs ----------memory---------- ---swap-- -----io---- --system-- -----cpu-----
r b swpd free buff cache si so bi bo in cs us sy id wa st
0 0 5 14 11 334 0 0 259 255 79 107 2 1 97 0 0
0 0 5 14 11 334 0 0 0 2 21 18 0 0 100 0 0
0 0 5 15 11 334 0 0 6 0 35 31 0 0 100 0 0
2 0 5 6 11 336 0 0 17100 7814 1378 2945 48 21 31 0 0
2 0 5 6 11 336 0 0 13193 14 1662 3343 78 22 0 0 0
2 0 5 13 11 330 0 0 11656 9781 1419 2642 82 18 0 0 0
2 0 5 9 11 334 0 0 10705 2716 1504 2657 81 19 0 0 0
1 0 5 14 11 336 0 0 6467 3788 765 1384 43 9 48 0 0
0 0 5 14 11 336 0 0 0 13 28 24 0 0 100 0 0
0 0 5 14 11 336 0 0 0 0 20 15 0 0 100 0 0
[root@RHEL65 ~]#
vmstat is also discussed in other chapters.
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troubleshooting tools
9.7. practice: troubleshooting tools
0. It is imperative that you practice these tools before trouble arises. It will help you get
familiar with the tools and allow you to create a base line of normal behaviour for your
systems.
1. Read the theory on fuser and explore its man page. Use this command to find files that
you open yourself.
2. Read the theory on lsof and explore its man page. Use this command to find files that
you open yourself.
3. Boot a live image on an existing computer (virtual or real) and chroot into to it.
4. Start one or more disk intensive jobs and monitor them with iostat and iotop (compare
to vmstat).
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troubleshooting tools
9.8. solution: troubleshooting tools
0. It is imperative that you practice these tools before trouble arises. It will help you get
familiar with the tools and allow you to create a base line of normal behaviour for your
systems.
1. Read the theory on fuser and explore its man page. Use this command to find files that
you open yourself.
2. Read the theory on lsof and explore its man page. Use this command to find files that
you open yourself.
3. Boot a live image on an existing computer (virtual or real) and chroot into to it.
4. Start one or more disk intensive jobs and monitor them with iostat and iotop (compare
to vmstat).
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Chapter 10. introduction to uuid's
A uuid or universally unique identifier is used to uniquely identify objects. This 128bit
standard allows anyone to create a unique uuid.
This chapter takes a brief look at uuid's.
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introduction to uuid's
10.1. about unique objects
Older versions of Linux have a vol_id utility to display the uuid of a file system.
root@debian5:~# vol_id --uuid /dev/sda1
193c3c9b-2c40-9290-8b71-4264ee4d4c82
Red Hat Enterprise Linux 5 puts vol_id in /lib/udev/vol_id, which is not in the $PATH. The
syntax is also a bit different from Debian/Ubuntu/Mint.
root@rhel53 ~# /lib/udev/vol_id -u /dev/hda1
48a6a316-9ca9-4214-b5c6-e7b33a77e860
This utility is not available in standard installations of RHEL6 or Debian6.
10.2. tune2fs
Use tune2fs to find the uuid of a file system.
[root@RHEL5 ~]# tune2fs -l /dev/sda1 | grep UUID
Filesystem UUID: 11cfc8bc-07c0-4c3f-9f64-78422ef1dd5c
[root@RHEL5 ~]# /lib/udev/vol_id -u /dev/sda1
11cfc8bc-07c0-4c3f-9f64-78422ef1dd5c
10.3. uuid
There is more information in the manual of uuid, a tool that can generate uuid's.
[root@rhel65 ~]# yum install uuid
(output truncated)
[root@rhel65 ~]# man uuid
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introduction to uuid's
10.4. uuid in /etc/fstab
You can use the uuid to make sure that a volume is universally uniquely identified in /etc/
fstab. The device name can change depending on the disk devices that are present at boot
time, but a uuid never changes.
First we use tune2fs to find the uuid.
[root@RHEL5 ~]# tune2fs -l /dev/sdc1 | grep UUID
Filesystem UUID: 7626d73a-2bb6-4937-90ca-e451025d64e8
Then we check that it is properly added to /etc/fstab, the uuid replaces the variable
devicename /dev/sdc1.
[root@RHEL5 ~]# grep UUID /etc/fstab
UUID=7626d73a-2bb6-4937-90ca-e451025d64e8 /home/pro42 ext3 defaults 0 0
Now we can mount the volume using the mount point defined in /etc/fstab.
[root@RHEL5 ~]# mount /home/pro42
[root@RHEL5 ~]# df -h | grep 42
/dev/sdc1 397M 11M 366M 3% /home/pro42
The real test now, is to remove /dev/sdb from the system, reboot the machine and see what
happens. After the reboot, the disk previously known as /dev/sdc is now /dev/sdb.
[root@RHEL5 ~]# tune2fs -l /dev/sdb1 | grep UUID
Filesystem UUID: 7626d73a-2bb6-4937-90ca-e451025d64e8
And thanks to the uuid in /etc/fstab, the mountpoint is mounted on the same disk as before.
[root@RHEL5 ~]# df -h | grep sdb
/dev/sdb1 397M 11M 366M 3% /home/pro42
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introduction to uuid's
10.5. uuid as a boot device
Recent Linux distributions (Debian, Ubuntu, ...) use grub with a uuid to identify the root
file system.
This example shows how a root=/dev/sda1 is replaced with a uuid.
title Ubuntu 9.10, kernel 2.6.31-19-generic
uuid f001ba5d-9077-422a-9634-8d23d57e782a
kernel /boot/vmlinuz-2.6.31-19-generic \
root=UUID=f001ba5d-9077-422a-9634-8d23d57e782a ro quiet splash
initrd /boot/initrd.img-2.6.31-19-generic
The screenshot above contains only four lines. The line starting with root= is the
continuation of the kernel line.
RHEL and CentOS boot from LVM after a default install.
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introduction to uuid's
10.6. practice: uuid and filesystems
1. Find the uuid of one of your ext3 partitions with tune2fs ( and vol_id if you are on
RHEL5).
2. Use this uuid in /etc/fstab and test that it works with a simple mount.
3. (optional) Test it also by removing a disk (so the device name is changed). You can edit
settings in vmware/Virtualbox to remove a hard disk.
4. Display the root= directive in /boot/grub/menu.lst. (We see later in the course how to
maintain this file.)
5. (optional on ubuntu) Replace the /dev/xxx in /boot/grub/menu.lst with a uuid (use an
extra stanza for this). Test that it works.
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introduction to uuid's
10.7. solution: uuid and filesystems
1. Find the uuid of one of your ext3 partitions with tune2fs ( and vol_id if you are on
RHEL5).
root@rhel55:~# /lib/udev/vol_id -u /dev/hda1
60926898-2c78-49b4-a71d-c1d6310c87cc
root@ubu1004:~# tune2fs -l /dev/sda2 | grep UUID
Filesystem UUID: 3007b743-1dce-2d62-9a59-cf25f85191b7
2. Use this uuid in /etc/fstab and test that it works with a simple mount.
tail -1 /etc/fstab
UUID=60926898-2c78-49b4-a71d-c1d6310c87cc /home/pro42 ext3 defaults 0 0
3. (optional) Test it also by removing a disk (so the device name is changed). You can edit
settings in vmware/Virtualbox to remove a hard disk.
4. Display the root= directive in /boot/grub/menu.lst. (We see later in the course how to
maintain this file.)
paul@deb503:~$ grep ^[^#] /boot/grub/menu.lst | grep root=
kernel /boot/vmlinuz-2.6.26-2-686 root=/dev/hda1 ro selinux=1 quiet
kernel /boot/vmlinuz-2.6.26-2-686 root=/dev/hda1 ro selinux=1 single
5. (optional on ubuntu) Replace the /dev/xxx in /boot/grub/menu.lst with a uuid (use an
extra stanza for this). Test that it works.
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Chapter 11. introduction to raid
11.1. hardware or software
Redundant Array of Independent (originally Inexpensive) Disks or RAID can be set up using
hardware or software. Hardware RAID is more expensive, but offers better performance.
Software RAID is cheaper and easier to manage, but it uses your CPU and your memory.
Where ten years ago nobody was arguing about the best choice being hardware RAID, this
has changed since technologies like mdadm, lvm and even zfs focus more on managability.
The workload on the cpu for software RAID used to be high, but cpu's have gotten a lot
faster.
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introduction to raid
11.2. raid levels
11.2.1. raid 0
raid 0 uses two or more disks, and is often called striping (or stripe set, or striped volume).
Data is divided in chunks, those chunks are evenly spread across every disk in the array.
The main advantage of raid 0 is that you can create larger drives. raid 0 is the only raid
without redundancy.
11.2.2. jbod
jbod uses two or more disks, and is often called concatenating (spanning, spanned set, or
spanned volume). Data is written to the first disk, until it is full. Then data is written to the
second disk... The main advantage of jbod (Just a Bunch of Disks) is that you can create
larger drives. JBOD offers no redundancy.
11.2.3. raid 1
raid 1 uses exactly two disks, and is often called mirroring (or mirror set, or mirrored
volume). All data written to the array is written on each disk. The main advantage of raid 1
is redundancy. The main disadvantage is that you lose at least half of your available disk
space (in other words, you at least double the cost).
11.2.4. raid 2, 3 and 4 ?
raid 2 uses bit level striping, raid 3 byte level, and raid 4 is the same as raid 5, but with a
dedicated parity disk. This is actually slower than raid 5, because every write would have
to write parity to this one (bottleneck) disk. It is unlikely that you will ever see these raid
levels in production.
11.2.5. raid 5
raid 5 uses three or more disks, each divided into chunks. Every time chunks are written
to the array, one of the disks will receive a parity chunk. Unlike raid 4, the parity chunk
will alternate between all disks. The main advantage of this is that raid 5 will allow for full
data recovery in case of one hard disk failure.
11.2.6. raid 6
raid 6 is very similar to raid 5, but uses two parity chunks. raid 6 protects against two hard
disk failures. Oracle Solaris zfs calls this raidz2 (and also had raidz3 with triple parity).
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introduction to raid
11.2.7. raid 0+1
raid 0+1 is a mirror(1) of stripes(0). This means you first create two raid 0 stripe sets, and
then you set them up as a mirror set. For example, when you have six 100GB disks, then
the stripe sets are each 300GB. Combined in a mirror, this makes 300GB total. raid 0+1
will survive one disk failure. It will only survive the second disk failure if this disk is in the
same stripe set as the previous failed disk.
11.2.8. raid 1+0
raid 1+0 is a stripe(0) of mirrors(1). For example, when you have six 100GB disks, then
you first create three mirrors of 100GB each. You then stripe them together into a 300GB
drive. In this example, as long as not all disks in the same mirror fail, it can survive up to
three hard disk failures.
11.2.9. raid 50
raid 5+0 is a stripe(0) of raid 5 arrays. Suppose you have nine disks of 100GB, then you
can create three raid 5 arrays of 200GB each. You can then combine them into one large
stripe set.
11.2.10. many others
There are many other nested raid combinations, like raid 30, 51, 60, 100, 150, ...
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introduction to raid
11.3. building a software raid5 array
11.3.1. do we have three disks?
First, you have to attach some disks to your computer. In this scenario, three brand new disks
of eight gigabyte each are added. Check with fdisk -l that they are connected.
[root@rhel6c ~]# fdisk -l 2> /dev/null | grep MB
Disk /dev/sdb: 8589 MB, 8589934592 bytes
Disk /dev/sdc: 8589 MB, 8589934592 bytes
Disk /dev/sdd: 8589 MB, 8589934592 bytes
11.3.2. fd partition type
The next step is to create a partition of type fd on every disk. The fd type is to set the partition
as Linux RAID autodetect. See this (truncated) screenshot:
[root@rhel6c ~]# fdisk /dev/sdd
...
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-1044, default 1):
Using default value 1
Last cylinder, +cylinders or +size{K,M,G} (1-1044, default 1044):
Using default value 1044
Command (m for help): t
Selected partition 1
Hex code (type L to list codes): fd
Changed system type of partition 1 to fd (Linux raid autodetect)
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
11.3.3. verify all three partitions
Now all three disks are ready for raid 5, so we have to tell the system what to do with these
disks.
[root@rhel6c ~]# fdisk -l 2> /dev/null | grep raid
/dev/sdb1 1 1044 8385898+ fd Linux raid autodetect
/dev/sdc1 1 1044 8385898+ fd Linux raid autodetect
/dev/sdd1 1 1044 8385898+ fd Linux raid autodetect
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introduction to raid
11.3.4. create the raid5
The next step used to be create the raid table in /etc/raidtab. Nowadays, you can just issue
the command mdadm with the correct parameters.
The command below is split on two lines to fit this print, but you should type it on one line,
without the backslash (\).
[root@rhel6c ~]# mdadm --create /dev/md0 --chunk=64 --level=5 --raid-\
devices=3 /dev/sdb1 /dev/sdc1 /dev/sdd1
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
Below a partial screenshot how fdisk -l sees the raid 5.
[root@rhel6c ~]# fdisk -l /dev/md0
Disk /dev/md0: 17.2 GB, 17172135936 bytes
2 heads, 4 sectors/track, 4192416 cylinders
Units = cylinders of 8 * 512 = 4096 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 65536 bytes / 131072 bytes
Disk identifier: 0x00000000
Disk /dev/md0 doesn't contain a valid partition table
We could use this software raid 5 array in the next topic: lvm.
11.3.5. /proc/mdstat
The status of the raid devices can be seen in /proc/mdstat. This example shows a raid 5
in the process of rebuilding.
[root@rhel6c ~]# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 sdd1[3] sdc1[1] sdb1[0]
16769664 blocks super 1.2 level 5, 64k chunk, algorithm 2 [3/2] [UU_]
[============>........] recovery = 62.8% (5266176/8384832) finish=0\
.3min speed=139200K/sec
This example shows an active software raid 5.
[root@rhel6c ~]# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active raid5 sdd1[3] sdc1[1] sdb1[0]
16769664 blocks super 1.2 level 5, 64k chunk, algorithm 2 [3/3] [UUU]
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introduction to raid
11.3.6. mdadm --detail
Use mdadm --detail to get information on a raid device.
[root@rhel6c ~]# mdadm --detail /dev/md0
/dev/md0:
Version : 1.2
Creation Time : Sun Jul 17 13:48:41 2011
Raid Level : raid5
Array Size : 16769664 (15.99 GiB 17.17 GB)
Used Dev Size : 8384832 (8.00 GiB 8.59 GB)
Raid Devices : 3
Total Devices : 3
Persistence : Superblock is persistent
Update Time : Sun Jul 17 13:49:43 2011
State : clean
Active Devices : 3
Working Devices : 3
Failed Devices : 0
Spare Devices : 0
Layout : left-symmetric
Chunk Size : 64K
Name : rhel6c:0 (local to host rhel6c)
UUID : c10fd9c3:08f9a25f:be913027:999c8e1f
Events : 18
Number Major Minor RaidDevice State
0 8 17 0 active sync /dev/sdb1
1 8 33 1 active sync /dev/sdc1
3 8 49 2 active sync /dev/sdd1
11.3.7. removing a software raid
The software raid is visible in /proc/mdstat when active. To remove the raid completely so
you can use the disks for other purposes, you stop (de-activate) it with mdadm.
[root@rhel6c ~]# mdadm --stop /dev/md0
mdadm: stopped /dev/md0
The disks can now be repartitioned.
11.3.8. further reading
Take a look at the man page of mdadm for more information. Below an example command
to add a new partition while removing a faulty one.
mdadm /dev/md0 --add /dev/sdd1 --fail /dev/sdb1 --remove /dev/sdb1
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11.4. practice: raid
1. Add three virtual disks of 1GB each to a virtual machine.
2. Create a software raid 5 on the three disks. (It is not necessary to put a filesystem on it)
3. Verify with fdisk and in /proc that the raid 5 exists.
4. Stop and remove the raid 5.
5. Create a raid 1 to mirror two disks.
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introduction to raid
11.5. solution: raid
1. Add three virtual disks of 1GB each to a virtual machine.
2. Create a software raid 5 on the three disks. (It is not necessary to put a filesystem on it)
3. Verify with fdisk and in /proc that the raid 5 exists.
4. Stop and remove the raid 5.
5. Create a raid 1 to mirror two disks.
[root@rhel6c ~]# mdadm --create /dev/md0 --level=1 --raid-devices=2 \
/dev/sdb1 /dev/sdc1
mdadm: Defaulting to version 1.2 metadata
mdadm: array /dev/md0 started.
[root@rhel6c ~]# cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4] [raid1]
md0 : active raid1 sdc1[1] sdb1[0]
8384862 blocks super 1.2 [2/2] [UU]
[====>................] resync = 20.8% (1745152/8384862) \
finish=0.5min speed=218144K/sec
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Chapter 12. logical volume
management
Most lvm implementations support physical storage grouping, logical volume resizing
and data migration.
Physical storage grouping is a fancy name for grouping multiple block devices (hard disks,
but also iSCSI etc) into a logical mass storage device. To enlarge this physical group, block
devices (including partitions) can be added at a later time.
The size of lvm volumes on this physical group is independent of the individual size of the
components. The total size of the group is the limit.
One of the nice features of lvm is the logical volume resizing. You can increase the size of
an lvm volume, sometimes even without any downtime. Additionally, you can migrate data
away from a failing hard disk device, create mirrors and create snapshots.
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12.1. introduction to lvm
12.1.1. problems with standard partitions
There are some problems when working with hard disks and standard partitions. Consider
a system with a small and a large hard disk device, partitioned like this. The first disk (/
dev/sda) is partitioned in two, the second disk (/dev/sdb) has two partitions and some empty
space.
In the example above, consider the options when you want to enlarge the space available
for /srv/project42. What can you do ? The solution will always force you to unmount the
file system, take a backup of the data, remove and recreate partitions, and then restore the
data and remount the file system.
12.1.2. solution with lvm
Using lvm will create a virtual layer between the mounted file systems and the hardware
devices. This virtual layer will allow for an administrator to enlarge a mounted file system in
use. When lvm is properly used, then there is no need to unmount the file system to enlarge it.
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logical volume management
12.2. lvm terminology
12.2.1. physical volume (pv)
A physical volume is any block device (a disk, a partition, a RAID device or even an iSCSI
device). All these devices can become a member of a volume group.
The commands used to manage a physical volume start with pv.
[root@centos65 ~]# pv
pvchange pvck pvcreate pvdisplay pvmove pvremove
pvresize pvs pvscan
12.2.2. volume group (vg)
A volume group is an abstraction layer between block devices and logical volumes.
The commands used to manage a volume group start with vg.
[root@centos65 ~]# vg
vgcfgbackup vgconvert vgextend vgmknodes vgs
vgcfgrestore vgcreate vgimport vgreduce vgscan
vgchange vgdisplay vgimportclone vgremove vgsplit
vgck vgexport vgmerge vgrename
12.2.3. logical volume (lv)
A logical volume is created in a volume group. Logical volumes that contain a file system
can be mounted. The use of logical volumes is similar to the use of partitions and is
accomplished with the same standard commands (mkfs, mount, fsck, df, ...).
The commands used to manage a logical volume start with lv.
[root@centos65 ~]# lv
lvchange lvextend lvmdiskscan lvmsar lvresize
lvconvert lvm lvmdump lvreduce lvs
lvcreate lvmchange lvmetad lvremove lvscan
lvdisplay lvmconf lvmsadc lvrename
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12.3. example: using lvm
This example shows how you can use a device (in this case /dev/sdc, but it could have been /
dev/sdb or any other disk or partition) with lvm, how to create a volume group (vg) and how
to create and use a logical volume (vg/lvol0).
First thing to do, is create physical volumes that can join the volume group with pvcreate.
This command makes a disk or partition available for use in Volume Groups. The screenshot
shows how to present the SCSI Disk device to LVM.
root@RHEL4:~# pvcreate /dev/sdc
Physical volume "/dev/sdc" successfully created
Note: lvm will work fine when using the complete device, but another operating system on the
same computer (or on the same SAN) will not recognize lvm and will mark the block device
as being empty! You can avoid this by creating a partition that spans the whole device, then
run pvcreate on the partition instead of the disk.
Then vgcreate creates a volume group using one device. Note that more devices could be
added to the volume group.
root@RHEL4:~# vgcreate vg /dev/sdc
Volume group "vg" successfully created
The last step lvcreate creates a logical volume.
root@RHEL4:~# lvcreate --size 500m vg
Logical volume "lvol0" created
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logical volume management
The logical volume /dev/vg/lvol0 can now be formatted with ext3, and mounted for normal
use.
root@RHELv4u2:~# mke2fs -m0 -j /dev/vg/lvol0
mke2fs 1.35 (28-Feb-2004)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
128016 inodes, 512000 blocks
0 blocks (0.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67633152
63 block groups
8192 blocks per group, 8192 fragments per group
2032 inodes per group
Superblock backups stored on blocks:
8193, 24577, 40961, 57345, 73729, 204801, 221185, 401409
Writing inode tables: done
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 37 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.
root@RHELv4u2:~# mkdir /home/project10
root@RHELv4u2:~# mount /dev/vg/lvol0 /home/project10/
root@RHELv4u2:~# df -h | grep proj
/dev/mapper/vg-lvol0 485M 11M 474M 3% /home/project10
A logical volume is very similar to a partition, it can be formatted with a file system, and
can be mounted so users can access it.
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logical volume management
12.4. example: extend a logical volume
A logical volume can be extended without unmounting the file system. Whether or not a
volume can be extended depends on the file system it uses. Volumes that are mounted as
vfat or ext2 cannot be extended, so in the example here we use the ext3 file system.
The fdisk command shows us newly added scsi-disks that will serve our lvm volume. This
volume will then be extended. First, take a look at these disks.
[root@RHEL5 ~]# fdisk -l | grep sd[bc]
Disk /dev/sdb doesn't contain a valid partition table
Disk /dev/sdc doesn't contain a valid partition table
Disk /dev/sdb: 1181 MB, 1181115904 bytes
Disk /dev/sdc: 429 MB, 429496320 bytes
You already know how to partition a disk, below the first disk is partitioned (in one big
primary partition), the second disk is left untouched.
[root@RHEL5 ~]# fdisk -l | grep sd[bc]
Disk /dev/sdc doesn't contain a valid partition table
Disk /dev/sdb: 1181 MB, 1181115904 bytes
/dev/sdb1 1 143 1148616 83 Linux
Disk /dev/sdc: 429 MB, 429496320 bytes
You also know how to prepare disks for lvm with pvcreate, and how to create a volume
group with vgcreate. This example adds both the partitioned disk and the untouched disk
to the volume group named vg2.
[root@RHEL5 ~]# pvcreate /dev/sdb1
Physical volume "/dev/sdb1" successfully created
[root@RHEL5 ~]# pvcreate /dev/sdc
Physical volume "/dev/sdc" successfully created
[root@RHEL5 ~]# vgcreate vg2 /dev/sdb1 /dev/sdc
Volume group "vg2" successfully created
You can use pvdisplay to verify that both the disk and the partition belong to the volume
group.
[root@RHEL5 ~]# pvdisplay | grep -B1 vg2
PV Name /dev/sdb1
VG Name vg2
--
PV Name /dev/sdc
VG Name vg2
And you are familiar both with the lvcreate command to create a small logical volume and
the mke2fs command to put ext3 on it.
[root@RHEL5 ~]# lvcreate --size 200m vg2
Logical volume "lvol0" created
[root@RHEL5 ~]# mke2fs -m20 -j /dev/vg2/lvol0
...
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As you see, we end up with a mounted logical volume that according to df is almost 200
megabyte in size.
[root@RHEL5 ~]# mkdir /home/resizetest
[root@RHEL5 ~]# mount /dev/vg2/lvol0 /home/resizetest/
[root@RHEL5 ~]# df -h | grep resizetest
194M 5.6M 149M 4% /home/resizetest
Extending the volume is easy with lvextend.
[root@RHEL5 ~]# lvextend -L +100 /dev/vg2/lvol0
Extending logical volume lvol0 to 300.00 MB
Logical volume lvol0 successfully resized
But as you can see, there is a small problem: it appears that df is not able to display the
extended volume in its full size. This is because the filesystem is only set for the size of the
volume before the extension was added.
[root@RHEL5 ~]# df -h | grep resizetest
194M 5.6M 149M 4% /home/resizetest
With lvdisplay however we can see that the volume is indeed extended.
[root@RHEL5 ~]# lvdisplay /dev/vg2/lvol0 | grep Size
LV Size 300.00 MB
To finish the extension, you need resize2fs to span the filesystem over the full size of the
logical volume.
[root@RHEL5 ~]# resize2fs /dev/vg2/lvol0
resize2fs 1.39 (29-May-2006)
Filesystem at /dev/vg2/lvol0 is mounted on /home/resizetest; on-line re\
sizing required
Performing an on-line resize of /dev/vg2/lvol0 to 307200 (1k) blocks.
The filesystem on /dev/vg2/lvol0 is now 307200 blocks long.
Congratulations, you just successfully expanded a logical volume.
[root@RHEL5 ~]# df -h | grep resizetest
291M 6.1M 225M 3% /home/resizetest
[root@RHEL5 ~]#
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12.5. example: resize a physical Volume
This is a humble demonstration of how to resize a physical Volume with lvm (after you
resize it with fdisk). The demonstration starts with a 100MB partition named /dev/sde1. We
used fdisk to create it, and to verify the size.
[root@RHEL5 ~]# fdisk -l 2>/dev/null | grep sde1
/dev/sde1 1 100 102384 83 Linux
[root@RHEL5 ~]#
Now we can use pvcreate to create the Physical Volume, followed by pvs to verify the
creation.
[root@RHEL5 ~]# pvcreate /dev/sde1
Physical volume "/dev/sde1" successfully created
[root@RHEL5 ~]# pvs | grep sde1
/dev/sde1 lvm2 -- 99.98M 99.98M
[root@RHEL5 ~]#
The next step is to use fdisk to enlarge the partition (actually deleting it and then recreating /
dev/sde1 with more cylinders).
[root@RHEL5 ~]# fdisk /dev/sde
Command (m for help): p
Disk /dev/sde: 858 MB, 858993152 bytes
64 heads, 32 sectors/track, 819 cylinders
Units = cylinders of 2048 * 512 = 1048576 bytes
Device Boot Start End Blocks Id System
/dev/sde1 1 100 102384 83 Linux
Command (m for help): d
Selected partition 1
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4):
Value out of range.
Partition number (1-4): 1
First cylinder (1-819, default 1):
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-819, default 819): 200
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
[root@RHEL5 ~]#
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When we now use fdisk and pvs to verify the size of the partition and the Physical Volume,
then there is a size difference. LVM is still using the old size.
[root@RHEL5 ~]# fdisk -l 2>/dev/null | grep sde1
/dev/sde1 1 200 204784 83 Linux
[root@RHEL5 ~]# pvs | grep sde1
/dev/sde1 lvm2 -- 99.98M 99.98M
[root@RHEL5 ~]#
Executing pvresize on the Physical Volume will make lvm aware of the size change of the
partition. The correct size can be displayed with pvs.
[root@RHEL5 ~]# pvresize /dev/sde1
Physical volume "/dev/sde1" changed
1 physical volume(s) resized / 0 physical volume(s) not resized
[root@RHEL5 ~]# pvs | grep sde1
/dev/sde1 lvm2 -- 199.98M 199.98M
[root@RHEL5 ~]#
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12.6. example: mirror a logical volume
We start by creating three physical volumes for lvm. Then we verify the creation and the
size with pvs. Three physical disks because lvm uses two disks for the mirror and a third
disk for the mirror log!
[root@RHEL5 ~]# pvcreate /dev/sdb /dev/sdc /dev/sdd
Physical volume "/dev/sdb" successfully created
Physical volume "/dev/sdc" successfully created
Physical volume "/dev/sdd" successfully created
[root@RHEL5 ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/sdb lvm2 -- 409.60M 409.60M
/dev/sdc lvm2 -- 409.60M 409.60M
/dev/sdd lvm2 -- 409.60M 409.60M
Then we create the Volume Group and verify again with pvs. Notice how the three physical
volumes now belong to vg33, and how the size is rounded down (in steps of the extent size,
here 4MB).
[root@RHEL5 ~]# vgcreate vg33 /dev/sdb /dev/sdc /dev/sdd
Volume group "vg33" successfully created
[root@RHEL5 ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda2 VolGroup00 lvm2 a- 15.88G 0
/dev/sdb vg33 lvm2 a- 408.00M 408.00M
/dev/sdc vg33 lvm2 a- 408.00M 408.00M
/dev/sdd vg33 lvm2 a- 408.00M 408.00M
[root@RHEL5 ~]#
The last step is to create the Logical Volume with lvcreate. Notice the -m 1 switch to create
one mirror. Notice also the change in free space in all three Physical Volumes!
[root@RHEL5 ~]# lvcreate --size 300m -n lvmir -m 1 vg33
Logical volume "lvmir" created
[root@RHEL5 ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda2 VolGroup00 lvm2 a- 15.88G 0
/dev/sdb vg33 lvm2 a- 408.00M 108.00M
/dev/sdc vg33 lvm2 a- 408.00M 108.00M
/dev/sdd vg33 lvm2 a- 408.00M 404.00M
You can see the copy status of the mirror with lvs. It currently shows a 100 percent copy.
[root@RHEL5 ~]# lvs vg33/lvmir
LV VG Attr LSize Origin Snap% Move Log Copy%
lvmir vg33 mwi-ao 300.00M lvmir_mlog 100.00
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12.7. example: snapshot a logical volume
A snapshot is a virtual copy of all the data at a point in time on a volume. A snapshot Logical
Volume will retain a copy of all changed files of the snapshotted Logical Volume.
The example below creates a snapshot of the bigLV Logical Volume.
[root@RHEL5 ~]# lvcreate -L100M -s -n snapLV vg42/bigLV
Logical volume "snapLV" created
[root@RHEL5 ~]#
You can see with lvs that the snapshot snapLV is indeed a snapshot of bigLV. Moments
after taking the snapshot, there are few changes to bigLV (0.02 percent).
[root@RHEL5 ~]# lvs
LV VG Attr LSize Origin Snap% Move Log Copy%
bigLV vg42 owi-a- 200.00M
snapLV vg42 swi-a- 100.00M bigLV 0.02
[root@RHEL5 ~]#
But after using bigLV for a while, more changes are done. This means the snapshot volume
has to keep more original data (10.22 percent).
[root@RHEL5 ~]# lvs | grep vg42
bigLV vg42 owi-ao 200.00M
snapLV vg42 swi-a- 100.00M bigLV 10.22
[root@RHEL5 ~]#
You can now use regular backup tools (dump, tar, cpio, ...) to take a backup of the snapshot
Logical Volume. This backup will contain all data as it existed on bigLV at the time the
snapshot was taken. When the backup is done, you can remove the snapshot.
[root@RHEL5 ~]# lvremove vg42/snapLV
Do you really want to remove active logical volume "snapLV"? [y/n]: y
Logical volume "snapLV" successfully removed
[root@RHEL5 ~]#
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12.8. verifying existing physical volumes
12.8.1. lvmdiskscan
To get a list of block devices that can be used with LVM, use lvmdiskscan. The example
below uses grep to limit the result to SCSI devices.
[root@RHEL5 ~]# lvmdiskscan | grep sd
/dev/sda1 [ 101.94 MB]
/dev/sda2 [ 15.90 GB] LVM physical volume
/dev/sdb [ 409.60 MB]
/dev/sdc [ 409.60 MB]
/dev/sdd [ 409.60 MB] LVM physical volume
/dev/sde1 [ 95.98 MB]
/dev/sde5 [ 191.98 MB]
/dev/sdf [ 819.20 MB] LVM physical volume
/dev/sdg1 [ 818.98 MB]
[root@RHEL5 ~]#
12.8.2. pvs
The easiest way to verify whether devices are known to lvm is with the pvs command. The
screenshot below shows that only /dev/sda2 is currently known for use with LVM. It shows
that /dev/sda2 is part of Volgroup00 and is almost 16GB in size. It also shows /dev/sdc and /
dev/sdd as part of vg33. The device /dev/sdb is knwon to lvm, but not linked to any Volume
Group.
[root@RHEL5 ~]# pvs
PV VG Fmt Attr PSize PFree
/dev/sda2 VolGroup00 lvm2 a- 15.88G 0
/dev/sdb lvm2 -- 409.60M 409.60M
/dev/sdc vg33 lvm2 a- 408.00M 408.00M
/dev/sdd vg33 lvm2 a- 408.00M 408.00M
[root@RHEL5 ~]#
12.8.3. pvscan
The pvscan command will scan all disks for existing Physical Volumes. The information is
similar to pvs, plus you get a line with total sizes.
[root@RHEL5 ~]# pvscan
PV /dev/sdc VG vg33 lvm2 [408.00 MB / 408.00 MB free]
PV /dev/sdd VG vg33 lvm2 [408.00 MB / 408.00 MB free]
PV /dev/sda2 VG VolGroup00 lvm2 [15.88 GB / 0 free]
PV /dev/sdb lvm2 [409.60 MB]
Total: 4 [17.07 GB] / in use: 3 [16.67 GB] / in no VG: 1 [409.60 MB]
[root@RHEL5 ~]#
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12.8.4. pvdisplay
Use pvdisplay to get more information about physical volumes. You can also use pvdisplay
without an argument to display information about all physical (lvm) volumes.
[root@RHEL5 ~]# pvdisplay /dev/sda2
--- Physical volume ---
PV Name /dev/sda2
VG Name VolGroup00
PV Size 15.90 GB / not usable 20.79 MB
Allocatable yes (but full)
PE Size (KByte) 32768
Total PE 508
Free PE 0
Allocated PE 508
PV UUID TobYfp-Ggg0-Rf8r-xtLd-5XgN-RSPc-8vkTHD
[root@RHEL5 ~]#
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12.9. verifying existing volume groups
12.9.1. vgs
Similar to pvs is the use of vgs to display a quick overview of all volume groups. There
is only one volume group in the screenshot below, it is named VolGroup00 and is almost
16GB in size.
[root@RHEL5 ~]# vgs
VG #PV #LV #SN Attr VSize VFree
VolGroup00 1 2 0 wz--n- 15.88G 0
[root@RHEL5 ~]#
12.9.2. vgscan
The vgscan command will scan all disks for existing Volume Groups. It will also update the
/etc/lvm/.cache file. This file contains a list of all current lvm devices.
[root@RHEL5 ~]# vgscan
Reading all physical volumes. This may take a while...
Found volume group "VolGroup00" using metadata type lvm2
[root@RHEL5 ~]#
LVM will run the vgscan automatically at boot-up, so if you add hot swap devices, then you
will need to run vgscan to update /etc/lvm/.cache with the new devices.
12.9.3. vgdisplay
The vgdisplay command will give you more detailed information about a volume group (or
about all volume groups if you omit the argument).
[root@RHEL5 ~]# vgdisplay VolGroup00
--- Volume group ---
VG Name VolGroup00
System ID
Format lvm2
Metadata Areas 1
Metadata Sequence No 3
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 2
Open LV 2
Max PV 0
Cur PV 1
Act PV 1
VG Size 15.88 GB
PE Size 32.00 MB
Total PE 508
Alloc PE / Size 508 / 15.88 GB
Free PE / Size 0 / 0
VG UUID qsXvJb-71qV-9l7U-ishX-FobM-qptE-VXmKIg
[root@RHEL5 ~]#
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12.10. verifying existing logical volumes
12.10.1. lvs
Use lvs for a quick look at all existing logical volumes. Below you can see two logical
volumes named LogVol00 and LogVol01.
[root@RHEL5 ~]# lvs
LV VG Attr LSize Origin Snap% Move Log Copy%
LogVol00 VolGroup00 -wi-ao 14.88G
LogVol01 VolGroup00 -wi-ao 1.00G
[root@RHEL5 ~]#
12.10.2. lvscan
The lvscan command will scan all disks for existing Logical Volumes.
[root@RHEL5 ~]# lvscan
ACTIVE '/dev/VolGroup00/LogVol00' [14.88 GB] inherit
ACTIVE '/dev/VolGroup00/LogVol01' [1.00 GB] inherit
[root@RHEL5 ~]#
12.10.3. lvdisplay
More detailed information about logical volumes is available through the lvdisplay(1)
command.
[root@RHEL5 ~]# lvdisplay VolGroup00/LogVol01
--- Logical volume ---
LV Name /dev/VolGroup00/LogVol01
VG Name VolGroup00
LV UUID RnTGK6-xWsi-t530-ksJx-7cax-co5c-A1KlDp
LV Write Access read/write
LV Status available
# open 1
LV Size 1.00 GB
Current LE 32
Segments 1
Allocation inherit
Read ahead sectors 0
Block device 253:1
[root@RHEL5 ~]#
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12.11. manage physical volumes
12.11.1. pvcreate
Use the pvcreate command to add devices to lvm. This example shows how to add a disk
(or hardware RAID device) to lvm.
[root@RHEL5 ~]# pvcreate /dev/sdb
Physical volume "/dev/sdb" successfully created
[root@RHEL5 ~]#
This example shows how to add a partition to lvm.
[root@RHEL5 ~]# pvcreate /dev/sdc1
Physical volume "/dev/sdc1" successfully created
[root@RHEL5 ~]#
You can also add multiple disks or partitions as target to pvcreate. This example adds three
disks to lvm.
[root@RHEL5 ~]# pvcreate /dev/sde /dev/sdf /dev/sdg
Physical volume "/dev/sde" successfully created
Physical volume "/dev/sdf" successfully created
Physical volume "/dev/sdg" successfully created
[root@RHEL5 ~]#
12.11.2. pvremove
Use the pvremove command to remove physical volumes from lvm. The devices may not
be in use.
[root@RHEL5 ~]# pvremove /dev/sde /dev/sdf /dev/sdg
Labels on physical volume "/dev/sde" successfully wiped
Labels on physical volume "/dev/sdf" successfully wiped
Labels on physical volume "/dev/sdg" successfully wiped
[root@RHEL5 ~]#
12.11.3. pvresize
When you used fdisk to resize a partition on a disk, then you must use pvresize to make lvm
recognize the new size of the physical volume that represents this partition.
[root@RHEL5 ~]# pvresize /dev/sde1
Physical volume "/dev/sde1" changed
1 physical volume(s) resized / 0 physical volume(s) not resized
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12.11.4. pvchange
With pvchange you can prevent the allocation of a Physical Volume in a new Volume Group
or Logical Volume. This can be useful if you plan to remove a Physical Volume.
[root@RHEL5 ~]# pvchange -xn /dev/sdd
Physical volume "/dev/sdd" changed
1 physical volume changed / 0 physical volumes not changed
[root@RHEL5 ~]#
To revert your previous decision, this example shows you how te re-enable the Physical
Volume to allow allocation.
[root@RHEL5 ~]# pvchange -xy /dev/sdd
Physical volume "/dev/sdd" changed
1 physical volume changed / 0 physical volumes not changed
[root@RHEL5 ~]#
12.11.5. pvmove
With pvmove you can move Logical Volumes from within a Volume Group to another
Physical Volume. This must be done before removing a Physical Volume.
[root@RHEL5 ~]# pvs | grep vg1
/dev/sdf vg1 lvm2 a- 816.00M 0
/dev/sdg vg1 lvm2 a- 816.00M 816.00M
[root@RHEL5 ~]# pvmove /dev/sdf
/dev/sdf: Moved: 70.1%
/dev/sdf: Moved: 100.0%
[root@RHEL5 ~]# pvs | grep vg1
/dev/sdf vg1 lvm2 a- 816.00M 816.00M
/dev/sdg vg1 lvm2 a- 816.00M 0
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12.12. manage volume groups
12.12.1. vgcreate
Use the vgcreate command to create a volume group. You can immediately name all the
physical volumes that span the volume group.
[root@RHEL5 ~]# vgcreate vg42 /dev/sde /dev/sdf
Volume group "vg42" successfully created
[root@RHEL5 ~]#
12.12.2. vgextend
Use the vgextend command to extend an existing volume group with a physical volume.
[root@RHEL5 ~]# vgextend vg42 /dev/sdg
Volume group "vg42" successfully extended
[root@RHEL5 ~]#
12.12.3. vgremove
Use the vgremove command to remove volume groups from lvm. The volume groups may
not be in use.
[root@RHEL5 ~]# vgremove vg42
Volume group "vg42" successfully removed
[root@RHEL5 ~]#
12.12.4. vgreduce
Use the vgreduce command to remove a Physical Volume from the Volume Group.
The following example adds Physical Volume /dev/sdg to the vg1 Volume Group using
vgextend. And then removes it again using vgreduce.
[root@RHEL5 ~]# pvs | grep sdg
/dev/sdg lvm2 -- 819.20M 819.20M
[root@RHEL5 ~]# vgextend vg1 /dev/sdg
Volume group "vg1" successfully extended
[root@RHEL5 ~]# pvs | grep sdg
/dev/sdg vg1 lvm2 a- 816.00M 816.00M
[root@RHEL5 ~]# vgreduce vg1 /dev/sdg
Removed "/dev/sdg" from volume group "vg1"
[root@RHEL5 ~]# pvs | grep sdg
/dev/sdg lvm2 -- 819.20M 819.20M
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12.12.5. vgchange
Use the vgchange command to change parameters of a Volume Group.
This example shows how to prevent Physical Volumes from being added or removed to the
Volume Group vg1.
[root@RHEL5 ~]# vgchange -xn vg1
Volume group "vg1" successfully changed
[root@RHEL5 ~]# vgextend vg1 /dev/sdg
Volume group vg1 is not resizable.
You can also use vgchange to change most other properties of a Volume Group. This
example changes the maximum number of Logical Volumes and maximum number of
Physical Volumes that vg1 can serve.
[root@RHEL5 ~]# vgdisplay vg1 | grep -i max
MAX LV 0
Max PV 0
[root@RHEL5 ~]# vgchange -l16 vg1
Volume group "vg1" successfully changed
[root@RHEL5 ~]# vgchange -p8 vg1
Volume group "vg1" successfully changed
[root@RHEL5 ~]# vgdisplay vg1 | grep -i max
MAX LV 16
Max PV 8
12.12.6. vgmerge
Merging two Volume Groups into one is done with vgmerge. The following example merges
vg2 into vg1, keeping all the properties of vg1.
[root@RHEL5 ~]# vgmerge vg1 vg2
Volume group "vg2" successfully merged into "vg1"
[root@RHEL5 ~]#
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12.13. manage logical volumes
12.13.1. lvcreate
Use the lvcreate command to create Logical Volumes in a Volume Group. This example
creates an 8GB Logical Volume in Volume Group vg42.
[root@RHEL5 ~]# lvcreate -L5G vg42
Logical volume "lvol0" created
[root@RHEL5 ~]#
As you can see, lvm automatically names the Logical Volume lvol0. The next example
creates a 200MB Logical Volume named MyLV in Volume Group vg42.
[root@RHEL5 ~]# lvcreate -L200M -nMyLV vg42
Logical volume "MyLV" created
[root@RHEL5 ~]#
The next example does the same thing, but with different syntax.
[root@RHEL5 ~]# lvcreate --size 200M -n MyLV vg42
Logical volume "MyLV" created
[root@RHEL5 ~]#
This example creates a Logical Volume that occupies 10 percent of the Volume Group.
[root@RHEL5 ~]# lvcreate -l 10%VG -n MyLV2 vg42
Logical volume "MyLV2" created
[root@RHEL5 ~]#
This example creates a Logical Volume that occupies 30 percent of the remaining free space
in the Volume Group.
[root@RHEL5 ~]# lvcreate -l 30%FREE -n MyLV3 vg42
Logical volume "MyLV3" created
[root@RHEL5 ~]#
12.13.2. lvremove
Use the lvremove command to remove Logical Volumes from a Volume Group. Removing
a Logical Volume requires the name of the Volume Group.
[root@RHEL5 ~]# lvremove vg42/MyLV
Do you really want to remove active logical volume "MyLV"? [y/n]: y
Logical volume "MyLV" successfully removed
[root@RHEL5 ~]#
Removing multiple Logical Volumes will request confirmation for each individual volume.
[root@RHEL5 ~]# lvremove vg42/MyLV vg42/MyLV2 vg42/MyLV3
Do you really want to remove active logical volume "MyLV"? [y/n]: y
Logical volume "MyLV" successfully removed
Do you really want to remove active logical volume "MyLV2"? [y/n]: y
Logical volume "MyLV2" successfully removed
Do you really want to remove active logical volume "MyLV3"? [y/n]: y
Logical volume "MyLV3" successfully removed
[root@RHEL5 ~]#
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12.13.3. lvextend
Extending the volume is easy with lvextend. This example extends a 200MB Logical
Volume with 100 MB.
[root@RHEL5 ~]# lvdisplay /dev/vg2/lvol0 | grep Size
LV Size 200.00 MB
[root@RHEL5 ~]# lvextend -L +100 /dev/vg2/lvol0
Extending logical volume lvol0 to 300.00 MB
Logical volume lvol0 successfully resized
[root@RHEL5 ~]# lvdisplay /dev/vg2/lvol0 | grep Size
LV Size 300.00 MB
The next example creates a 100MB Logical Volume, and then extends it to 500MB.
[root@RHEL5 ~]# lvcreate --size 100M -n extLV vg42
Logical volume "extLV" created
[root@RHEL5 ~]# lvextend -L 500M vg42/extLV
Extending logical volume extLV to 500.00 MB
Logical volume extLV successfully resized
[root@RHEL5 ~]#
This example doubles the size of a Logical Volume.
[root@RHEL5 ~]# lvextend -l+100%LV vg42/extLV
Extending logical volume extLV to 1000.00 MB
Logical volume extLV successfully resized
[root@RHEL5 ~]#
12.13.4. lvrename
Renaming a Logical Volume is done with lvrename. This example renames extLV to bigLV
in the vg42 Volume Group.
[root@RHEL5 ~]# lvrename vg42/extLV vg42/bigLV
Renamed "extLV" to "bigLV" in volume group "vg42"
[root@RHEL5 ~]#
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12.14. practice : lvm
1. Create a volume group that contains a complete disk and a partition on another disk.
2. Create two logical volumes (a small one and a bigger one) in this volumegroup. Format
them wih ext3, mount them and copy some files to them.
3. Verify usage with fdisk, mount, pvs, vgs, lvs, pvdisplay, vgdisplay, lvdisplay and df. Does
fdisk give you any information about lvm?
4. Enlarge the small logical volume by 50 percent, and verify your work!
5. Take a look at other commands that start with vg* , pv* or lv*.
6. Create a mirror and a striped Logical Volume.
7. Convert a linear logical volume to a mirror.
8. Convert a mirror logical volume to a linear.
9. Create a snapshot of a Logical Volume, take a backup of the snapshot. Then delete some
files on the Logical Volume, then restore your backup.
10. Move your volume group to another disk (keep the Logical Volumes mounted).
11. If time permits, split a Volume Group with vgsplit, then merge it again with vgmerge.
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12.15. solution : lvm
1. Create a volume group that contains a complete disk and a partition on another disk.
step 1: select disks:
root@rhel65:~# fdisk -l | grep Disk
Disk /dev/sda: 8589 MB, 8589934592 bytes
Disk identifier: 0x00055ca0
Disk /dev/sdb: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sdc: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
...
I choose /dev/sdb and /dev/sdc for now.
step 2: partition /dev/sdc
root@rhel65:~# fdisk /dev/sdc
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disk\
label
Building a new DOS disklabel with disk identifier 0x94c0e5d5.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.
Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)
WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
switch off the mode (command 'c') and change display units to
sectors (command 'u').
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-130, default 1):
Using default value 1
Last cylinder, +cylinders or +size{K,M,G} (1-130, default 130):
Using default value 130
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
step 3: pvcreate and vgcreate
root@rhel65:~# pvcreate /dev/sdb /dev/sdc1
Physical volume "/dev/sdb" successfully created
Physical volume "/dev/sdc1" successfully created
root@rhel65:~# vgcreate VG42 /dev/sdb /dev/sdc1
Volume group "VG42" successfully created
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2. Create two logical volumes (a small one and a bigger one) in this volumegroup. Format
them wih ext3, mount them and copy some files to them.
root@rhel65:~# lvcreate --size 200m --name LVsmall VG42
Logical volume "LVsmall" created
root@rhel65:~# lvcreate --size 600m --name LVbig VG42
Logical volume "LVbig" created
root@rhel65:~# ls -l /dev/mapper/VG42-LVsmall
lrwxrwxrwx. 1 root root 7 Apr 20 20:41 /dev/mapper/VG42-LVsmall -> ../dm-2
root@rhel65:~# ls -l /dev/VG42/LVsmall
lrwxrwxrwx. 1 root root 7 Apr 20 20:41 /dev/VG42/LVsmall -> ../dm-2
root@rhel65:~# ls -l /dev/dm-2
brw-rw----. 1 root disk 253, 2 Apr 20 20:41 /dev/dm-2
root@rhel65:~# mkfs.ext3 /dev/mapper/VG42-LVsmall
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
Stride=0 blocks, Stripe width=0 blocks
51200 inodes, 204800 blocks
10240 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67371008
25 block groups
8192 blocks per group, 8192 fragments per group
2048 inodes per group
Superblock backups stored on blocks:
8193, 24577, 40961, 57345, 73729
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 39 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.
root@rhel65:~# mkfs.ext3 /dev/VG42/LVbig
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
38400 inodes, 153600 blocks
7680 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=159383552
5 block groups
32768 blocks per group, 32768 fragments per group
7680 inodes per group
Superblock backups stored on blocks:
32768, 98304
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 25 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.
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The mounting and copying of files.
root@rhel65:~# mkdir /srv/LVsmall
root@rhel65:~# mkdir /srv/LVbig
root@rhel65:~# mount /dev/mapper/VG42-LVsmall /srv/LVsmall
root@rhel65:~# mount /dev/VG42/LVbig /srv/LVbig
root@rhel65:~# cp -r /etc /srv/LVsmall/
root@rhel65:~# cp -r /var/log /srv/LVbig/
3. Verify usage with fdisk, mount, pvs, vgs, lvs, pvdisplay, vgdisplay, lvdisplay and df. Does
fdisk give you any information about lvm?
Run all those commands (only two are shown below), then answer 'no'.
root@rhel65:~# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/VolGroup-lv_root
6.7G 1.4G 5.0G 21% /
tmpfs 246M 0 246M 0% /dev/shm
/dev/sda1 485M 77M 383M 17% /boot
/dev/mapper/VG42-LVsmall
194M 30M 154M 17% /srv/LVsmall
/dev/mapper/VG42-LVbig
591M 20M 541M 4% /srv/LVbig
root@rhel65:~# mount | grep VG42
/dev/mapper/VG42-LVsmall on /srv/LVsmall type ext3 (rw)
/dev/mapper/VG42-LVbig on /srv/LVbig type ext3 (rw)
4. Enlarge the small logical volume by 50 percent, and verify your work!
root@rhel65:~# lvextend VG42/LVsmall -l+50%LV
Extending logical volume LVsmall to 300.00 MiB
Logical volume LVsmall successfully resized
root@rhel65:~# resize2fs /dev/mapper/VG42-LVsmall
resize2fs 1.41.12 (17-May-2010)
Filesystem at /dev/mapper/VG42-LVsmall is mounted on /srv/LVsmall; on-line res\
izing required
old desc_blocks = 1, new_desc_blocks = 2
Performing an on-line resize of /dev/mapper/VG42-LVsmall to 307200 (1k) blocks.
The filesystem on /dev/mapper/VG42-LVsmall is now 307200 blocks long.
root@rhel65:~# df -h | grep small
/dev/mapper/VG42-LVsmall
291M 31M 246M 12% /srv/LVsmall
root@rhel65:~#
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5. Take a look at other commands that start with vg* , pv* or lv*.
6. Create a mirror and a striped Logical Volume.
7. Convert a linear logical volume to a mirror.
8. Convert a mirror logical volume to a linear.
9. Create a snapshot of a Logical Volume, take a backup of the snapshot. Then delete some
files on the Logical Volume, then restore your backup.
10. Move your volume group to another disk (keep the Logical Volumes mounted).
11. If time permits, split a Volume Group with vgsplit, then merge it again with vgmerge.
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Chapter 13. iSCSI devices
This chapter teaches you how to setup an iSCSI target server and an iSCSI initiator client.
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iSCSI devices
13.1. iSCSI terminology
iSCSI is a protocol that enables SCSI over IP. This means that you can have local SCSI
devices (like /dev/sdb) without having the storage hardware in the local computer.
The computer holding the physical storage hardware is called the iSCSI Target. Each
individual addressable iSCSI device on the target server will get a LUN number.
The iSCSI client computer that is connecting to the Target server is called an Initiator. An
initiator will send SCSI commands over IP instead of directly to the hardware. The Initiator
will connect to the Target.
13.2. iSCSI Target in RHEL/CentOS
This section will describe iSCSI Target setup on RHEL6, RHEL7 and CentOS.
Start with installing the iSCSI Target package.
yum install scsi-target-utils
We configure three local disks in /etc/tgt/targets.conf to become three LUN's.
<target iqn.2008-09.com.example:server.target2>
direct-store /dev/sdb
direct-store /dev/sdc
direct-store /dev/sdd
incominguser paul hunter2
</target>
Restart the service.
[root@centos65 ~]# service tgtd start
Starting SCSI target daemon: [ OK ]
The standard local port for iSCSI Target is 3260, in case of doubt you can verify this with
netstat.
[root@server1 tgt]# netstat -ntpl | grep tgt
tcp 0 0 0.0.0.0:3260 0.0.0.0:* LISTEN 1670/tgtd
tcp 0 0 :::3260 :::* LISTEN 1670/tgtd
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iSCSI devices
The tgt-admin -s command should now give you a nice overview of the three LUN's (and
also LUN 0 for the controller).
[root@server1 tgt]# tgt-admin -s
Target 1: iqn.2014-04.be.linux-training:server1.target1
System information:
Driver: iscsi
State: ready
I_T nexus information:
LUN information:
LUN: 0
Type: controller
SCSI ID: IET 00010000
SCSI SN: beaf10
Size: 0 MB, Block size: 1
Online: Yes
Removable media: No
Prevent removal: No
Readonly: No
Backing store type: null
Backing store path: None
Backing store flags:
LUN: 1
Type: disk
SCSI ID: IET 00010001
SCSI SN: VB9f23197b-af6cfb60
Size: 1074 MB, Block size: 512
Online: Yes
Removable media: No
Prevent removal: No
Readonly: No
Backing store type: rdwr
Backing store path: /dev/sdb
Backing store flags:
LUN: 2
Type: disk
SCSI ID: IET 00010002
SCSI SN: VB8f554351-a1410828
Size: 1074 MB, Block size: 512
Online: Yes
Removable media: No
Prevent removal: No
Readonly: No
Backing store type: rdwr
Backing store path: /dev/sdc
Backing store flags:
LUN: 3
Type: disk
SCSI ID: IET 00010003
SCSI SN: VB1035d2f0-7ae90b49
Size: 1074 MB, Block size: 512
Online: Yes
Removable media: No
Prevent removal: No
Readonly: No
Backing store type: rdwr
Backing store path: /dev/sdd
Backing store flags:
Account information:
ACL information:
ALL
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13.3. iSCSI Initiator in RHEL/CentOS
This section will describe iSCSI Initiator setup on RHEL6, RHEL7 and CentOS.
Start with installing the iSCSI Initiator package.
[root@server2 ~]# yum install iscsi-initiator-utils
Then ask the iSCSI target server to send you the target names.
[root@server2 ~]# iscsiadm -m discovery -t sendtargets -p 192.168.1.95:3260
Starting iscsid: [ OK ]
192.168.1.95:3260,1 iqn.2014-04.be.linux-training:centos65.target1
We received iqn.2014-04.be.linux-training:centos65.target1.
We use this iqn to configure the username and the password (paul and hunter2) that we set
on the target server.
[root@server2 iscsi]# iscsiadm -m node --targetname iqn.2014-04.be.linux-tra\
ining:centos65.target1 --portal "192.168.1.95:3260" --op=update --name node.\
session.auth.username --value=paul
[root@server2 iscsi]# iscsiadm -m node --targetname iqn.2014-04.be.linux-tra\
ining:centos65.target1 --portal "192.168.1.95:3260" --op=update --name node.\
session.auth.password --value=hunter2
[root@server2 iscsi]# iscsiadm -m node --targetname iqn.2014-04.be.linux-tra\
ining:centos65.target1 --portal "192.168.1.95:3260" --op=update --name node.\
session.auth.authmethod --value=CHAP
RHEL and CentOS will store these in /var/lib/iscsi/nodes/.
[root@server2 iscsi]# grep auth /var/lib/iscsi/nodes/iqn.2014-04.be.linux-tr\
aining\:centos65.target1/192.168.1.95\,3260\,1/default
node.session.auth.authmethod = CHAP
node.session.auth.username = paul
node.session.auth.password = hunter2
node.conn[0].timeo.auth_timeout = 45
[root@server2 iscsi]#
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iSCSI devices
A restart of the iscsi service will add three new devices to our system.
[root@server2 iscsi]# fdisk -l | grep Disk
Disk /dev/sda: 42.9 GB, 42949672960 bytes
Disk identifier: 0x0004f229
Disk /dev/sdb: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sdc: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sdd: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sde: 2147 MB, 2147483648 bytes
Disk identifier: 0x00000000
Disk /dev/sdf: 2147 MB, 2147483648 bytes
Disk identifier: 0x00000000
Disk /dev/sdg: 2147 MB, 2147483648 bytes
Disk identifier: 0x00000000
Disk /dev/mapper/VolGroup-lv_root: 41.4 GB, 41448112128 bytes
Disk identifier: 0x00000000
Disk /dev/mapper/VolGroup-lv_swap: 973 MB, 973078528 bytes
Disk identifier: 0x00000000
[root@server2 iscsi]# service iscsi restart
Stopping iscsi: [ OK ]
Starting iscsi: [ OK ]
[root@server2 iscsi]# fdisk -l | grep Disk
Disk /dev/sda: 42.9 GB, 42949672960 bytes
Disk identifier: 0x0004f229
Disk /dev/sdb: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sdc: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sdd: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sde: 2147 MB, 2147483648 bytes
Disk identifier: 0x00000000
Disk /dev/sdf: 2147 MB, 2147483648 bytes
Disk identifier: 0x00000000
Disk /dev/sdg: 2147 MB, 2147483648 bytes
Disk identifier: 0x00000000
Disk /dev/mapper/VolGroup-lv_root: 41.4 GB, 41448112128 bytes
Disk identifier: 0x00000000
Disk /dev/mapper/VolGroup-lv_swap: 973 MB, 973078528 bytes
Disk identifier: 0x00000000
Disk /dev/sdh: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sdi: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sdj: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
You can verify iscsi status with:
service iscsi status
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13.4. iSCSI target on Debian
Installing the software for the target server requires iscsitarget on Ubuntu and Debian, and
an extra iscsitarget-dkms for the kernel modules only on Debian.
root@debby6:~# aptitude install iscsitarget
The following NEW packages will be installed:
iscsitarget
0 packages upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 69.4 kB of archives. After unpacking 262 kB will be used.
Get:1 http://ftp.belnet.be/debian/ squeeze/main iscsitarget i386 1.4.20.2-1\
[69.4 kB]
Fetched 69.4 kB in 0s (415 kB/s)
Selecting previously deselected package iscsitarget.
(Reading database ... 36441 files and directories currently installed.)
Unpacking iscsitarget (from .../iscsitarget_1.4.20.2-1_i386.deb) ...
Processing triggers for man-db ...
Setting up iscsitarget (1.4.20.2-1) ...
iscsitarget not enabled in "/etc/default/iscsitarget", not starting...(warning).
On Debian 6 you will also need aptitude install iscsitarget-dkms for the kernel modules,
on Debian 5 this is aptitude install iscsitarget-modules-`uname -a`. Ubuntu includes the
kernel modules in the main package.
The iSCSI target server is disabled by default, so we enable it.
root@debby6:~# cat /etc/default/iscsitarget
ISCSITARGET_ENABLE=false
root@debby6:~# vi /etc/default/iscsitarget
root@debby6:~# cat /etc/default/iscsitarget
ISCSITARGET_ENABLE=true
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iSCSI devices
13.5. iSCSI target setup with dd files
You can use LVM volumes (/dev/md0/lvol0), physical partitions (/dev/sda) ,raid devices (/
dev/md0) or just plain files for storage. In this demo, we use files created with dd.
This screenshot shows how to create three small files (100MB, 200MB and 300MB).
root@debby6:~# mkdir /iscsi
root@debby6:~# dd if=/dev/zero of=/iscsi/lun1.img bs=1M count=100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 0.315825 s, 332 MB/s
root@debby6:~# dd if=/dev/zero of=/iscsi/lun2.img bs=1M count=200
200+0 records in
200+0 records out
209715200 bytes (210 MB) copied, 1.08342 s, 194 MB/s
root@debby6:~# dd if=/dev/zero of=/iscsi/lun3.img bs=1M count=300
300+0 records in
300+0 records out
314572800 bytes (315 MB) copied, 1.36209 s, 231 MB/s
We need to declare these three files as iSCSI targets in /etc/iet/ietd.conf (used to be /etc/
ietd.conf).
root@debby6:/etc/iet# cp ietd.conf ietd.conf.original
root@debby6:/etc/iet# > ietd.conf
root@debby6:/etc/iet# vi ietd.conf
root@debby6:/etc/iet# cat ietd.conf
Target iqn.2010-02.be.linux-training:storage.lun1
IncomingUser isuser hunter2
OutgoingUser
Lun 0 Path=/iscsi/lun1.img,Type=fileio
Alias LUN1
Target iqn.2010-02.be.linux-training:storage.lun2
IncomingUser isuser hunter2
OutgoingUser
Lun 0 Path=/iscsi/lun2.img,Type=fileio
Alias LUN2
Target iqn.2010-02.be.linux-training:storage.lun3
IncomingUser isuser hunter2
OutgoingUser
Lun 0 Path=/iscsi/lun3.img,Type=fileio
Alias LUN3
We also need to add our devices to the /etc/initiators.allow file.
root@debby6:/etc/iet# cp initiators.allow initiators.allow.original
root@debby6:/etc/iet# >initiators.allow
root@debby6:/etc/iet# vi initiators.allow
root@debby6:/etc/iet# cat initiators.allow
iqn.2010-02.be.linux-training:storage.lun1
iqn.2010-02.be.linux-training:storage.lun2
iqn.2010-02.be.linux-training:storage.lun3
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iSCSI devices
Time to start the server now:
root@debby6:/etc/iet# /etc/init.d/iscsitarget start
Starting iSCSI enterprise target service:.
.
root@debby6:/etc/iet#
Verify activation of the storage devices in /proc/net/iet:
root@debby6:/etc/iet# cat /proc/net/iet/volume
tid:3 name:iqn.2010-02.be.linux-training:storage.lun3
lun:0 state:0 iotype:fileio iomode:wt blocks:614400 blocksize:\
512 path:/iscsi/lun3.img
tid:2 name:iqn.2010-02.be.linux-training:storage.lun2
lun:0 state:0 iotype:fileio iomode:wt blocks:409600 blocksize:\
512 path:/iscsi/lun2.img
tid:1 name:iqn.2010-02.be.linux-training:storage.lun1
lun:0 state:0 iotype:fileio iomode:wt blocks:204800 blocksize:\
512 path:/iscsi/lun1.img
root@debby6:/etc/iet# cat /proc/net/iet/session
tid:3 name:iqn.2010-02.be.linux-training:storage.lun3
tid:2 name:iqn.2010-02.be.linux-training:storage.lun2
tid:1 name:iqn.2010-02.be.linux-training:storage.lun1
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iSCSI devices
13.6. ISCSI initiator on ubuntu
First we install the iSCSi client software (on another computer than the target).
root@ubu1104:~# aptitude install open-iscsi
Reading package lists... Done
Building dependency tree
Reading state information... Done
Reading extended state information
Initializing package states... Done
The following NEW packages will be installed:
open-iscsi open-iscsi-utils{a}
Then we set the iSCSI client to start automatically.
root@ubu1104:/etc/iscsi# cp iscsid.conf iscsid.conf.original
root@ubu1104:/etc/iscsi# vi iscsid.conf
root@ubu1104:/etc/iscsi# grep ^node.startup iscsid.conf
node.startup = automatic
Or you could start it manually.
root@ubu1104:/etc/iscsi/nodes# /etc/init.d/open-iscsi start
* Starting iSCSI initiator service iscsid [ OK ]
* Setting up iSCSI targets [ OK ]
root@ubu1104:/etc/iscsi/nodes#
Now we can connect to the Target server and use iscsiadm to discover the devices it offers:
root@ubu1104:/etc/iscsi# iscsiadm -m discovery -t st -p 192.168.1.31
192.168.1.31:3260,1 iqn.2010-02.be.linux-training:storage.lun2
192.168.1.31:3260,1 iqn.2010-02.be.linux-training:storage.lun1
192.168.1.31:3260,1 iqn.2010-02.be.linux-training:storage.lun3
We can use the same iscsiadm to edit the files in /etc/iscsi/nodes/.
root@ubu1104:/etc/iscsi# iscsiadm -m node --targetname "iqn.2010-02.be.linu\
x-training:storage.lun1" --portal "192.168.1.31:3260" --op=update --name no\
de.session.auth.authmethod --value=CHAP
root@ubu1104:/etc/iscsi# iscsiadm -m node --targetname "iqn.2010-02.be.linu\
x-training:storage.lun1" --portal "192.168.1.31:3260" --op=update --name no\
de.session.auth.username --value=isuser
root@ubu1104:/etc/iscsi# iscsiadm -m node --targetname "iqn.2010-02.be.linu\
x-training:storage.lun1" --portal "192.168.1.31:3260" --op=update --name no\
de.session.auth.password --value=hunter2
Repeat the above for the other two devices.
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iSCSI devices
Restart the initiator service to log in to the target.
root@ubu1104:/etc/iscsi/nodes# /etc/init.d/open-iscsi restart
* Disconnecting iSCSI targets [ OK ]
* Stopping iSCSI initiator service [ OK ]
* Starting iSCSI initiator service iscsid [ OK ]
* Setting up iSCSI targets
Use fdisk -l to enjoy three new iSCSI devices.
root@ubu1104:/etc/iscsi/nodes# fdisk -l 2> /dev/null | grep Disk
Disk /dev/sda: 17.2 GB, 17179869184 bytes
Disk identifier: 0x0001983f
Disk /dev/sdb: 209 MB, 209715200 bytes
Disk identifier: 0x00000000
Disk /dev/sdd: 314 MB, 314572800 bytes
Disk identifier: 0x00000000
Disk /dev/sdc: 104 MB, 104857600 bytes
Disk identifier: 0x00000000
The Target (the server) now shows active sessions.
root@debby6:/etc/iet# cat /proc/net/iet/session
tid:3 name:iqn.2010-02.be.linux-training:storage.lun3
sid:5348024611832320 initiator:iqn.1993-08.org.debian:01:8983ed2d770
cid:0 ip:192.168.1.35 state:active hd:none dd:none
tid:2 name:iqn.2010-02.be.linux-training:storage.lun2
sid:4785074624856576 initiator:iqn.1993-08.org.debian:01:8983ed2d770
cid:0 ip:192.168.1.35 state:active hd:none dd:none
tid:1 name:iqn.2010-02.be.linux-training:storage.lun1
sid:5066549618344448 initiator:iqn.1993-08.org.debian:01:8983ed2d770
cid:0 ip:192.168.1.35 state:active hd:none dd:none
root@debby6:/etc/iet#
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iSCSI devices
13.7. using iSCSI devices
There is no difference between using SCSI or iSCSI devices once they are connected :
partition, make filesystem, mount.
root@ubu1104:/etc/iscsi/nodes# history | tail -13
94 fdisk /dev/sdc
95 fdisk /dev/sdd
96 fdisk /dev/sdb
97 mke2fs /dev/sdb1
98 mke2fs -j /dev/sdc1
99 mkfs.ext4 /dev/sdd1
100 mkdir /mnt/is1
101 mkdir /mnt/is2
102 mkdir /mnt/is3
103 mount /dev/sdb1 /mnt/is1
104 mount /dev/sdc1 /mnt/is2
105 mount /dev/sdd1 /mnt/is3
106 history | tail -13
root@ubu1104:/etc/iscsi/nodes# mount | grep is
/dev/sdb1 on /mnt/is1 type ext2 (rw)
/dev/sdc1 on /mnt/is2 type ext3 (rw)
/dev/sdd1 on /mnt/is3 type ext4 (rw)
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iSCSI devices
13.8. iSCSI Target RHEL7/CentOS7
The prefered tool to setup an iSCSI Target on RHEL is targetcli.
[root@centos7 ~]# yum install targetcli
Loaded plugins: fastestmirror
...
...
Installed:
targetcli.noarch 0:2.1.fb37-3.el7
Complete!
[root@centos7 ~]#
The targetcli tool is interactive and represents the configuration fo the target in a structure
that resembles a directory tree with several files. Although this is explorable inside targetcli
with ls, cd and pwd, this are not files on the file system.
This tool also has tab-completion, which is very handy for the iqn names.
[root@centos7 ~]# targetcli
targetcli shell version 2.1.fb37
Copyright 2011-2013 by Datera, Inc and others.
For help on commands, type 'help'.
/> cd backstores/
/backstores> ls
o- backstores ............................................................ [...]
o- block ................................................ [Storage Objects: 0]
o- fileio ............................................... [Storage Objects: 0]
o- pscsi ................................................ [Storage Objects: 0]
o- ramdisk .............................................. [Storage Objects: 0]
/backstores> cd block
/backstores/block> ls
o- block .................................................. [Storage Objects: 0]
/backstores/block> create server1.disk1 /dev/sdb
Created block storage object server1.disk1 using /dev/sdb.
/backstores/block> ls
o- block .................................................. [Storage Objects: 1]
o- server1.disk1 .................. [/dev/sdb (2.0GiB) write-thru deactivated]
/backstores/block> cd /iscsi
/iscsi> create iqn.2015-04.be.linux:iscsi1
Created target iqn.2015-04.be.linux:iscsi1.
Created TPG 1.
Global pref auto_add_default_portal=true
Created default portal listening on all IPs (0.0.0.0), port 3260.
/iscsi> cd /iscsi/iqn.2015-04.be.linux:iscsi1/tpg1/acls
/iscsi/iqn.20...si1/tpg1/acls> create iqn.2015-04.be.linux:server2
Created Node ACL for iqn.2015-04.be.linux:server2
/iscsi/iqn.20...si1/tpg1/acls> cd iqn.2015-04.be.linux:server2
/iscsi/iqn.20...linux:server2> set auth userid=paul
Parameter userid is now 'paul'.
/iscsi/iqn.20...linux:server2> set auth password=hunter2
Parameter password is now 'hunter2'.
/iscsi/iqn.20...linux:server2> cd /iscsi/iqn.2015-04.be.linux:iscsi1/tpg1/luns
/iscsi/iqn.20...si1/tpg1/luns> create /backstores/block/server1.disk1
Created LUN 0.
Created LUN 0->0 mapping in node ACL iqn.2015-04.be.linux:server2
s/scsi/iqn.20...si1/tpg1/luns> cd /iscsi/iqn.2015-04.be.linux:iscsi1/tpg1/portals
/iscsi/iqn.20.../tpg1/portals> create 192.168.1.128
Using default IP port 3260
Could not create NetworkPortal in configFS.
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iSCSI devices
/iscsi/iqn.20.../tpg1/portals> cd /
/> ls
o- / ..................................................................... [...]
o- backstores .......................................................... [...]
| o- block .............................................. [Storage Objects: 1]
| | o- server1.disk1 ................ [/dev/sdb (2.0GiB) write-thru activated]
| o- fileio ............................................. [Storage Objects: 0]
| o- pscsi .............................................. [Storage Objects: 0]
| o- ramdisk ............................................ [Storage Objects: 0]
o- iscsi ........................................................ [Targets: 1]
| o- iqn.2015-04.be.linux:iscsi1 ................................... [TPGs: 1]
| o- tpg1 ........................................... [no-gen-acls, no-auth]
| o- acls ...................................................... [ACLs: 1]
| | o- iqn.2015-04.be.linux:server2 ..................... [Mapped LUNs: 1]
| | o- mapped_lun0 ..................... [lun0 block/server1.disk1 (rw)]
| o- luns ...................................................... [LUNs: 1]
| | o- lun0 ............................. [block/server1.disk1 (/dev/sdb)]
| o- portals ................................................ [Portals: 1]
| o- 0.0.0.0:3260 ................................................. [OK]
o- loopback ..................................................... [Targets: 0]
/> saveconfig
Last 10 configs saved in /etc/target/backup.
Configuration saved to /etc/target/saveconfig.json
/> exit
Global pref auto_save_on_exit=true
Last 10 configs saved in /etc/target/backup.
Configuration saved to /etc/target/saveconfig.json
[root@centos7 ~]#
Use the systemd tools to manage the service:
[root@centos7 ~]# systemctl enable target
ln -s '/usr/lib/systemd/system/target.service' '/etc/systemd/system/multi-user.target.wants/tar
[root@centos7 ~]# systemctl start target
[root@centos7 ~]#
Depending on your organisations policy, you may need to configure firewall and SELinux.
The screenshot belows adds a firewall rule to allow all traffic over port 3260, and disables
SELinux.
[root@centos7 ~]# firewall-cmd --permanent --add-port=3260/tcp
[root@centos7 ~]# firewall-cmd --reload
[root@centos7 ~]# setenforce 0
The total configuration is visible using ls from the root.
[root@centos7 ~]# targetcli
targetcli shell version 2.1.fb37
Copyright 2011-2013 by Datera, Inc and others.
For help on commands, type 'help'.
/> ls
o- / ..................................................................... [...]
o- backstores .......................................................... [...]
| o- block .............................................. [Storage Objects: 1]
| | o- server1.disk1 ................ [/dev/sdb (2.0GiB) write-thru activated]
| o- fileio ............................................. [Storage Objects: 0]
| o- pscsi .............................................. [Storage Objects: 0]
| o- ramdisk ............................................ [Storage Objects: 0]
o- iscsi ........................................................ [Targets: 1]
| o- iqn.2015-04.be.linux:iscsi1 ................................... [TPGs: 1]
| o- tpg1 ........................................... [no-gen-acls, no-auth]
| o- acls ...................................................... [ACLs: 1]
142
iSCSI devices
| | o- iqn.2015-04.be.linux:server2 ..................... [Mapped LUNs: 1]
| | o- mapped_lun0 ..................... [lun0 block/server1.disk1 (rw)]
| o- luns ...................................................... [LUNs: 1]
| | o- lun0 ............................. [block/server1.disk1 (/dev/sdb)]
| o- portals ................................................ [Portals: 1]
| o- 0.0.0.0:3260 ................................................. [OK]
o- loopback ..................................................... [Targets: 0]
/>
/> exit
Global pref auto_save_on_exit=true
Last 10 configs saved in /etc/target/backup.
Configuration saved to /etc/target/saveconfig.json
[root@centos7 ~]#
The iSCSI Target is now ready.
13.9. iSCSI Initiator RHEL7/CentOS7
This is identical to the RHEL6/CentOS6 procedure:
[root@centos7 ~]# yum install iscsi-initiator-utils
Loaded plugins: fastestmirror
...
...
Installed:
iscsi-initiator-utils.x86_64 0:6.2.0.873-29.el7
Dependency Installed:
iscsi-initiator-utils-iscsiuio.x86_64 0:6.2.0.873-29.el7
Complete!
Map your initiator name to the targetcli acl.
[root@centos7 ~]# cat /etc/iscsi/initiatorname.iscsi
InitiatorName=iqn.2015-04.be.linux:server2
[root@centos7 ~]#
Enter the CHAP authentication in /etc/iscsi/iscsid.conf.
[root@centos7 ~]# vi /etc/iscsi/iscsid.conf
...
[root@centos7 ~]# grep ^node.session.auth /etc/iscsi/iscsid.conf
node.session.auth.authmethod = CHAP
node.session.auth.username = paul
node.session.auth.password = hunter2
[root@centos7 ~]#
There are no extra devices yet...
[root@centos7 ~]# fdisk -l | grep sd
Disk /dev/sda: 22.0 GB, 22038806528 bytes, 43044544 sectors
/dev/sda1 * 2048 1026047 512000 83 Linux
/dev/sda2 1026048 43042815 21008384 8e Linux LVM
Disk /dev/sdb: 2147 MB, 2147483648 bytes, 4194304 sectors
Enable the service and discover the target.
[root@centos7 ~]# systemctl enable iscsid
ln -s '/usr/lib/systemd/system/iscsid.service' '/etc/systemd/system/multi-user.target.wants/isc
[root@centos7 ~]# iscsiadm -m discovery -t st -p 192.168.1.128
192.168.1.128:3260,1 iqn.2015-04.be.linux:iscsi1
143
iSCSI devices
Log into the target and see /dev/sdc appear.
[root@centos7 ~]# iscsiadm -m node -T iqn.2015-04.be.linux:iscsi1 -p 192.168.1.128 -l
Logging in to [iface: default, target: iqn.2015-04.be.linux:iscsi1, portal: 192.168.1.128,3260]
Login to [iface: default, target: iqn.2015-04.be.linux:iscsi1, portal: 192.168.1.128,3260] succ
[root@centos7 ~]#
[root@centos7 ~]# fdisk -l | grep sd
Disk /dev/sda: 22.0 GB, 22038806528 bytes, 43044544 sectors
/dev/sda1 * 2048 1026047 512000 83 Linux
/dev/sda2 1026048 43042815 21008384 8e Linux LVM
Disk /dev/sdb: 2147 MB, 2147483648 bytes, 4194304 sectors
Disk /dev/sdc: 2147 MB, 2147483648 bytes, 4194304 sectors
[root@centos7 ~]#
144
iSCSI devices
13.10. practice: iSCSI devices
1. Set up a target (using an LVM and a SCSI device) and an initiator that connects to both.
2. Set up an iSCSI Target and Initiator on two CentOS7/RHEL7 computers with the
following information:
Table 13.1. iSCSI Target and Initiator practice
variable value
Target Server IP
shared devices on target /dev/sd /dev/sd /dev/sd
shared device name sd
shared device name sd
shared device name sd
target iqn
initiator iqn
username
password
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iSCSI devices
13.11. solution: iSCSI devices
1. Set up a target (using an LVM and a SCSI device) and an initiator that connects to both.
This solution was done on Debian/ubuntu/Mint. For RHEL/CentOS check the theory.
Decide (with a partner) on a computer to be the Target and another computer to be the
Initiator.
On the Target computer:
First install iscsitarget using the standard tools for installing software in your distribution.
Then use your knowledge from the previous chapter to setup a logical volume (/dev/vg/
lvol0) and use the RAID chapter to setup /dev/md0. Then perform the following step:
vi /etc/default/iscsitarget (set enable to true)
Add your devices to /etc/iet/ietf.conf
root@debby6:/etc/iet# cat ietd.conf
Target iqn.2010-02.be.linux-training:storage.lun1
IncomingUser isuser hunter2
OutgoingUser
Lun 0 Path=/dev/vg/lvol0,Type=fileio
Alias LUN1
Target iqn.2010-02.be.linux-training:storage.lun2
IncomingUser isuser hunter2
OutgoingUser
Lun 0 Path=/dev/md0,Type=fileio
Alias LUN2
Add both devices to /etc/iet/initiators.allow
root@debby6:/etc/iet# cat initiators.allow
iqn.2010-02.be.linux-training:storage.lun1
iqn.2010-02.be.linux-training:storage.lun2
Now start the iscsitarget daemon and move over to the Initiator.
On the Initiator computer:
Install open-iscsi and start the daemon.
Then use iscsiadm -m discovery -t st -p 'target-ip' to see the iscsi devices on the Target.
Edit the files /etc/iscsi/nodes/ as shown in the book. Then restart the iSCSI daemon and
rund fdisk -l to see the iSCSI devices.
146
iSCSI devices
2. Set up an iSCSI Target and Initiator on two CentOS7/RHEL7 computers with the
following information:
Table 13.2. iSCSI Target and Initiator practice
variable value
Target Server IP 192.168.1.143 (Adjust for your subnet!)
shared devices on target /dev/sdb /dev/sdc /dev/sdd
shared device name sdb target.disk1
shared device name sdc target.disk2
shared device name sdd target.disk3
target iqn iqn.2015-04.be.linux:target
initiator iqn iqn.2015-04.be.linux:initiator
username paul
password hunter2
On the iSCSI Target server:
[root@centos7 ~]# targetcli
targetcli shell version 2.1.fb37
Copyright 2011-2013 by Datera, Inc and others.
For help on commands, type 'help'.
/> cd /backstores/block
/backstores/block> ls
o- block .................................................. [Storage Objects: 0]
/backstores/block> create target.disk1 /dev/sdb
Created block storage object target.disk1 using /dev/sdb.
/backstores/block> create target.disk2 /dev/sdc
Created block storage object target.disk2 using /dev/sdc.
/backstores/block> create target.disk3 /dev/sdd
Created block storage object target.disk3 using /dev/sdd.
/backstores/block> ls
o- block .................................................. [Storage Objects: 3]
o- target.disk1 ................... [/dev/sdb (8.0GiB) write-thru deactivated]
o- target.disk2 ................... [/dev/sdc (8.0GiB) write-thru deactivated]
o- target.disk3 ................... [/dev/sdd (8.0GiB) write-thru deactivated]
/backstores/block> cd /iscsi
/iscsi> create iqn.2015-04.be.linux:target
Created target iqn.2015-04.be.linux:target.
Created TPG 1.
Global pref auto_add_default_portal=true
Created default portal listening on all IPs (0.0.0.0), port 3260.
/iscsi> cd /iscsi/iqn.2015-04.be.linux:target/tpg1/acls
/iscsi/iqn.20...get/tpg1/acls> create iqn.2015-04.be.linux:initiator
Created Node ACL for iqn.2015-04.be.linux:initiator
/iscsi/iqn.20...get/tpg1/acls> cd iqn.2015-04.be.linux:initiator
/iscsi/iqn.20...nux:initiator> pwd
/iscsi/iqn.2015-04.be.linux:target/tpg1/acls/iqn.2015-04.be.linux:initiator
/iscsi/iqn.20...nux:initiator> set auth userid=paul
Parameter userid is now 'paul'.
/iscsi/iqn.20...nux:initiator> set auth password=hunter2
Parameter password is now 'hunter2'.
/iscsi/iqn.20...nux:initiator> cd /iscsi/iqn.2015-04.be.linux:target/tpg1/
/iscsi/iqn.20...x:target/tpg1> ls
o- tpg1 ................................................. [no-gen-acls, no-auth]
o- acls ............................................................ [ACLs: 1]
| o- iqn.2015-04.be.linux:initiator ......................... [Mapped LUNs: 0]
147
iSCSI devices
o- luns ............................................................ [LUNs: 0]
o- portals ...................................................... [Portals: 1]
o- 0.0.0.0:3260 ....................................................... [OK]
/iscsi/iqn.20...x:target/tpg1> cd luns
/iscsi/iqn.20...get/tpg1/luns> create /backstores/block/target.disk1
Created LUN 0.
Created LUN 0->0 mapping in node ACL iqn.2015-04.be.linux:initiator
/iscsi/iqn.20...get/tpg1/luns> create /backstores/block/target.disk2
Created LUN 1.
Created LUN 1->1 mapping in node ACL iqn.2015-04.be.linux:initiator
/iscsi/iqn.20...get/tpg1/luns> create /backstores/block/target.disk3
Created LUN 2.
Created LUN 2->2 mapping in node ACL iqn.2015-04.be.linux:initiator
s/scsi/iqn.20...get/tpg1/luns> cd /iscsi/iqn.2015-04.be.linux:target/tpg1/portals
/iscsi/iqn.20.../tpg1/portals> create 192.168.1.143
Using default IP port 3260
Could not create NetworkPortal in configFS.
/iscsi/iqn.20.../tpg1/portals> cd /
/> ls
o- / ..................................................................... [...]
o- backstores .......................................................... [...]
| o- block .............................................. [Storage Objects: 3]
| | o- target.disk1 ................. [/dev/sdb (8.0GiB) write-thru activated]
| | o- target.disk2 ................. [/dev/sdc (8.0GiB) write-thru activated]
| | o- target.disk3 ................. [/dev/sdd (8.0GiB) write-thru activated]
| o- fileio ............................................. [Storage Objects: 0]
| o- pscsi .............................................. [Storage Objects: 0]
| o- ramdisk ............................................ [Storage Objects: 0]
o- iscsi ........................................................ [Targets: 1]
| o- iqn.2015-04.be.linux:target ................................... [TPGs: 1]
| o- tpg1 ........................................... [no-gen-acls, no-auth]
| o- acls ...................................................... [ACLs: 1]
| | o- iqn.2015-04.be.linux:initiator ................... [Mapped LUNs: 3]
| | o- mapped_lun0 ...................... [lun0 block/target.disk1 (rw)]
| | o- mapped_lun1 ...................... [lun1 block/target.disk2 (rw)]
| | o- mapped_lun2 ...................... [lun2 block/target.disk3 (rw)]
| o- luns ...................................................... [LUNs: 3]
| | o- lun0 .............................. [block/target.disk1 (/dev/sdb)]
| | o- lun1 .............................. [block/target.disk2 (/dev/sdc)]
| | o- lun2 .............................. [block/target.disk3 (/dev/sdd)]
| o- portals ................................................ [Portals: 1]
| o- 0.0.0.0:3260 ................................................. [OK]
o- loopback ..................................................... [Targets: 0]
/> exit
Global pref auto_save_on_exit=true
Last 10 configs saved in /etc/target/backup.
Configuration saved to /etc/target/saveconfig.json
[root@centos7 ~]# systemctl enable target
ln -s '/usr/lib/systemd/system/target.service' '/etc/systemd/system/multi-user.target.wants/tar
[root@centos7 ~]# systemctl start target
[root@centos7 ~]# setenforce 0
On the Initiator:
[root@centos7 ~]# cat /etc/iscsi/initiatorname.iscsi
InitiatorName=iqn.2015-04.be.linux:initiator
[root@centos7 ~]# vi /etc/iscsi/iscsid.conf
[root@centos7 ~]# grep ^node.session.au /etc/iscsi/iscsid.conf
node.session.auth.authmethod = CHAP
node.session.auth.username = paul
node.session.auth.password = hunter2
[root@centos7 ~]# fdisk -l 2>/dev/null | grep sd
Disk /dev/sda: 22.0 GB, 22038806528 bytes, 43044544 sectors
/dev/sda1 * 2048 1026047 512000 83 Linux
148
iSCSI devices
/dev/sda2 1026048 43042815 21008384 8e Linux LVM
Disk /dev/sdb: 8589 MB, 8589934592 bytes, 16777216 sectors
/dev/sdb1 2048 821247 409600 83 Linux
/dev/sdb2 821248 1640447 409600 83 Linux
/dev/sdb3 1640448 2459647 409600 83 Linux
Disk /dev/sdc: 8589 MB, 8589934592 bytes, 16777216 sectors
Disk /dev/sdd: 8589 MB, 8589934592 bytes, 16777216 sectors
Disk /dev/sde: 2147 MB, 2147483648 bytes, 4194304 sectors
Disk /dev/sdf: 2147 MB, 2147483648 bytes, 4194304 sectors
[root@centos7 ~]# systemctl enable iscsid
ln -s '/usr/lib/systemd/system/iscsid.service' '/etc/systemd/system/multi-user.target.wants/isc
[root@centos7 ~]# iscsiadm -m node -T iqn.2015-04.be.linux:target -p 192.168.1.143 -l
Logging in to [iface: default, target: iqn.2015-04.be.linux:target, portal: 192.168.1.143,3260]
Login to [iface: default, target: iqn.2015-04.be.linux:target, portal: 192.168.1.143,3260] succ
[root@centos7 ~]# fdisk -l 2>/dev/null | grep sd
Disk /dev/sda: 22.0 GB, 22038806528 bytes, 43044544 sectors
/dev/sda1 * 2048 1026047 512000 83 Linux
/dev/sda2 1026048 43042815 21008384 8e Linux LVM
Disk /dev/sdb: 8589 MB, 8589934592 bytes, 16777216 sectors
/dev/sdb1 2048 821247 409600 83 Linux
/dev/sdb2 821248 1640447 409600 83 Linux
/dev/sdb3 1640448 2459647 409600 83 Linux
Disk /dev/sdc: 8589 MB, 8589934592 bytes, 16777216 sectors
Disk /dev/sdd: 8589 MB, 8589934592 bytes, 16777216 sectors
Disk /dev/sde: 2147 MB, 2147483648 bytes, 4194304 sectors
Disk /dev/sdf: 2147 MB, 2147483648 bytes, 4194304 sectors
Disk /dev/sdg: 8589 MB, 8589934592 bytes, 16777216 sectors
Disk /dev/sdh: 8589 MB, 8589934592 bytes, 16777216 sectors
Disk /dev/sdi: 8589 MB, 8589934592 bytes, 16777216 sectors
[root@centos7 ~]#
149
Chapter 14. introduction to
multipathing
150
introduction to multipathing
14.1. install multipath
RHEL and CentOS need the device-mapper-multipath package.
yum install device-mapper-multipath
This will create a sample multipath.conf in /usr/share/doc/device-mapper-
multipath-0.4.9/multipath.conf.
There is no /etc/multipath.conf until you initialize it with mpathconf.
[root@server2 ~]# mpathconf --enable --with_multipathd y
Starting multipathd daemon: [ OK ]
[root@server2 ~]# wc -l /etc/multipath.conf
99 /etc/multipath.conf
14.2. configure multipath
You can now choose to either edit /etc/multipath.conf or use mpathconf to change this
file for you.
[root@server2 ~]# grep user_friendly_names /etc/multipath.conf
user_friendly_names yes
# user_friendly_names yes
[root@server2 ~]# mpathconf --enable --user_friendly_names n
[root@server2 ~]# grep user_friendly_names /etc/multipath.conf
user_friendly_names no
# user_friendly_names yes
[root@server2 ~]# mpathconf --enable --user_friendly_names y
[root@server2 ~]# grep user_friendly_names /etc/multipath.conf
user_friendly_names yes
# user_friendly_names yes
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introduction to multipathing
14.3. network
This example uses three networks, make sure the iSCSI Target is connected to all three
networks.
[root@server1 tgt]# ifconfig | grep -B1 192.168
eth1 Link encap:Ethernet HWaddr 08:00:27:4E:AB:8E
inet addr:192.168.1.98 Bcast:192.168.1.255 Mask:255.255.255.0
--
eth2 Link encap:Ethernet HWaddr 08:00:27:3F:A9:D1
inet addr:192.168.2.98 Bcast:192.168.2.255 Mask:255.255.255.0
--
eth3 Link encap:Ethernet HWaddr 08:00:27:94:52:26
inet addr:192.168.3.98 Bcast:192.168.3.255 Mask:255.255.255.0
The same must be true for the multipath Initiator:
[root@server2 ~]# ifconfig | grep -B1 192.168
eth1 Link encap:Ethernet HWaddr 08:00:27:A1:43:41
inet addr:192.168.1.99 Bcast:192.168.1.255 Mask:255.255.255.0
--
eth2 Link encap:Ethernet HWaddr 08:00:27:12:A8:70
inet addr:192.168.2.99 Bcast:192.168.2.255 Mask:255.255.255.0
--
eth3 Link encap:Ethernet HWaddr 08:00:27:6E:99:9B
inet addr:192.168.3.99 Bcast:192.168.3.255 Mask:255.255.255.0
Test the triple discovery in three networks (screenshot newer than above).
[root@centos7 ~]# iscsiadm -m discovery -t st -p 192.168.1.150
192.168.1.150:3260,1 iqn.2015-04.be.linux:target1
[root@centos7 ~]# iscsiadm -m discovery -t st -p 192.168.2.150
192.168.2.150:3260,1 iqn.2015-04.be.linux:target1
[root@centos7 ~]# iscsiadm -m discovery -t st -p 192.168.3.150
192.168.3.150:3260,1 iqn.2015-04.be.linux:target1
14.4. start multipathd and iscsi
Time to start (or restart) both the multipathd and iscsi services:
[root@server2 ~]# service multipathd restart
Stopping multipathd daemon: [ OK ]
Starting multipathd daemon: [ OK ]
[root@server2 ~]# service iscsi restart
Stopping iscsi: [ OK ]
Starting iscsi: [ OK ]
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introduction to multipathing
This shows fdisk output when leaving the default friendly_names option to yes. The bottom
three are the multipath devices to use.
[root@server2 ~]# fdisk -l | grep Disk
Disk /dev/sda: 42.9 GB, 42949672960 bytes
Disk identifier: 0x0004f229
Disk /dev/sdb: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sdc: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sdd: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sde: 2147 MB, 2147483648 bytes
Disk identifier: 0x00000000
Disk /dev/sdf: 2147 MB, 2147483648 bytes
Disk identifier: 0x00000000
Disk /dev/sdg: 2147 MB, 2147483648 bytes
Disk identifier: 0x00000000
Disk /dev/mapper/VolGroup-lv_root: 41.4 GB, 41448112128 bytes
Disk identifier: 0x00000000
Disk /dev/mapper/VolGroup-lv_swap: 973 MB, 973078528 bytes
Disk identifier: 0x00000000
Disk /dev/sdh: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sdi: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sdj: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sdl: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sdn: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sdk: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sdm: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sdp: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/sdo: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/mapper/mpathh: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/mapper/mpathi: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
Disk /dev/mapper/mpathj: 1073 MB, 1073741824 bytes
Disk identifier: 0x00000000
[root@server2 ~]#
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introduction to multipathing
14.5. multipath list
You can list the multipath connections and devices with multipath -ll.
[root@server2 ~]# multipath -ll
mpathj (1IET 00010001) dm-4 Reddy,VBOX HARDDISK
size=1.0G features='0' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=1 status=active
| `- 13:0:0:1 sdh 8:112 active ready running
|-+- policy='round-robin 0' prio=1 status=enabled
| `- 12:0:0:1 sdi 8:128 active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
`- 14:0:0:1 sdm 8:192 active ready running
mpathi (1IET 00010003) dm-3 Reddy,VBOX HARDDISK
size=1.0G features='0' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=1 status=active
| `- 13:0:0:3 sdk 8:160 active ready running
|-+- policy='round-robin 0' prio=1 status=enabled
| `- 12:0:0:3 sdn 8:208 active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
`- 14:0:0:3 sdp 8:240 active ready running
mpathh (1IET 00010002) dm-2 Reddy,VBOX HARDDISK
size=1.0G features='0' hwhandler='0' wp=rw
|-+- policy='round-robin 0' prio=1 status=active
| `- 12:0:0:2 sdl 8:176 active ready running
|-+- policy='round-robin 0' prio=1 status=enabled
| `- 13:0:0:2 sdj 8:144 active ready running
`-+- policy='round-robin 0' prio=1 status=enabled
`- 14:0:0:2 sdo 8:224 active ready running
[root@server2 ~]#
The IET (iSCSI Enterprise Target) ID should match the ones you see on the Target server.
[root@server1 ~]# tgt-admin -s | grep -e LUN -e IET -e dev
LUN information:
LUN: 0
SCSI ID: IET 00010000
LUN: 1
SCSI ID: IET 00010001
Backing store path: /dev/sdb
LUN: 2
SCSI ID: IET 00010002
Backing store path: /dev/sdc
LUN: 3
SCSI ID: IET 00010003
Backing store path: /dev/sdd
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introduction to multipathing
14.6. using the device
The rest is standard mkfs, mkdir, mount:
[root@server2 ~]# mkfs.ext4 /dev/mapper/mpathi
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
65536 inodes, 262144 blocks
13107 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=268435456
8 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376
Writing inode tables: done
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 38 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.
[root@server2 ~]# mkdir /srv/multipath
[root@server2 ~]# mount /dev/mapper/mpathi /srv/multipath/
[root@server2 ~]# df -h /srv/multipath/
Filesystem Size Used Avail Use% Mounted on
/dev/mapper/mpathi 1008M 34M 924M 4% /srv/multipath
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introduction to multipathing
14.7. practice: multipathing
1. Find a partner and decide who will be iSCSI Target and who will be iSCSI Initiator and
Multipather. Set up Multipath as we did in the theory.
2. Uncomment the big 'defaults' section in /etc/multipath.conf and disable friendly names.
Verify that multipath can work. You may need to check the manual for /lib/dev/scsi_id and
for multipath.conf.
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introduction to multipathing
14.8. solution: multipathing
1. Find a partner and decide who will be iSCSI Target and who will be iSCSI Initiator and
Multipather. Set up Multipath as we did in the theory.
Look in the theory...
2. Uncomment the big 'defaults' section in /etc/multipath.conf and disable friendly names.
Verify that multipath can work. You may need to check the manual for /lib/dev/scsi_id and
for multipath.conf.
vi multipath.conf
remove # for the big defaults section
add # for the very small one with friendly_names active
add the --replace-whitespace option to scsi_id.
defaults {
udev_dir /dev
polling_interval 10
path_selector "round-robin 0"
path_grouping_policy multibus
getuid_callout "/lib/udev/scsi_id --whitelisted --replace\
-whitespace --device=/dev/%n"
prio const
path_checker readsector0
rr_min_io 100
max_fds 8192
rr_weight priorities
failback immediate
no_path_retry fail
user_friendly_names no
}
The names now (after service restart) look like:
root@server2 etc]# multipath -ll
1IET_00010001 dm-8 Reddy,VBOX HARDDISK
size=1.0G features='0' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=1 status=active
|- 17:0:0:1 sdh 8:112 active ready running
|- 16:0:0:1 sdi 8:128 active ready running
`- 15:0:0:1 sdn 8:208 active ready running
1IET_00010003 dm-10 Reddy,VBOX HARDDISK
size=1.0G features='0' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=1 status=active
|- 17:0:0:3 sdl 8:176 active ready running
|- 16:0:0:3 sdm 8:192 active ready running
`- 15:0:0:3 sdp 8:240 active ready running
1IET_00010002 dm-9 Reddy,VBOX HARDDISK
size=1.0G features='0' hwhandler='0' wp=rw
`-+- policy='round-robin 0' prio=1 status=active
|- 17:0:0:2 sdj 8:144 active ready running
|- 16:0:0:2 sdk 8:160 active ready running
`- 15:0:0:2 sdo 8:224 active ready running
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introduction to multipathing
Did you blacklist your own devices ?
vi multipath.conf
--> search for blacklist:
add
devnode "^sd[a-g]"
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Part III. backup management
Table of Contents
15. backup ................................................................................................................................................... 161
15.1. About tape devices .................................................................................................................... 161
15.2. Compression .............................................................................................................................. 162
15.3. tar ............................................................................................................................................... 162
15.4. Backup Types ............................................................................................................................ 164
15.5. dump and restore ...................................................................................................................... 165
15.6. cpio ............................................................................................................................................ 165
15.7. dd ............................................................................................................................................... 166
15.8. split ............................................................................................................................................ 167
15.9. practice: backup ........................................................................................................................ 167
160
Chapter 15. backup
15.1. About tape devices
Don't forget that the name of a device strictly speaking has no meaning since the kernel will
use the major and minor number to find the hardware! See the man page of mknod and the
devices.txt file in the Linux kernel source for more info.
15.1.1. SCSI tapes
On the official Linux device list (http://www.lanana.org/docs/device-list/) we find the names
for SCSI tapes (major 9 char). SCSI tape devices are located underneath /dev/st and are
numbered starting with 0 for the first tape device.
/dev/st0 First tape device
/dev/st1 Second tape device
/dev/st2 Third tape device
To prevent automatic rewinding of tapes, prefix them with the letter n.
/dev/nst0 First no rewind tape device
/dev/nst1 Second no rewind tape device
/dev/nst2 Third no rewind tape device
By default, SCSI tapes on Linux will use the highest hardware compression that is supported
by the tape device. To lower the compression level, append one of the letters l (low), m
(medium) or a (auto) to the tape name.
/dev/st0l First low compression tape device
/dev/st0m First medium compression tape device
/dev/nst2m Third no rewind medium compression tape device
15.1.2. IDE tapes
On the official Linux device list (http://www.lanana.org/docs/device-list/) we find the names
for IDE tapes (major 37 char). IDE tape devices are located underneath /dev/ht and are
numbered starting with 0 for the first tape device. No rewind and compression is similar
to SCSI tapes.
/dev/ht0 First IDE tape device
/dev/nht0 Second no rewind IDE tape device
/dev/ht0m First medium compression IDE tape device
15.1.3. mt
To manage your tapes, use mt (Magnetic Tape). Some examples.
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backup
To receive information about the status of the tape.
mt -f /dev/st0 status
To rewind a tape...
mt -f /dev/st0 rewind
To rewind and eject a tape...
mt -f /dev/st0 eject
To erase a tape...
mt -f /dev/st0 erase
15.2. Compression
It can be beneficial to compress files before backup. The two most popular tools for
compression of regular files on Linux are gzip/gunzip and bzip2/bunzip2. Below you can
see gzip in action, notice that it adds the .gz extension to the file.
paul@RHELv4u4:~/test$ ls -l allfiles.tx*
-rw-rw-r-- 1 paul paul 8813553 Feb 27 05:38 allfiles.txt
paul@RHELv4u4:~/test$ gzip allfiles.txt
paul@RHELv4u4:~/test$ ls -l allfiles.tx*
-rw-rw-r-- 1 paul paul 931863 Feb 27 05:38 allfiles.txt.gz
paul@RHELv4u4:~/test$ gunzip allfiles.txt.gz
paul@RHELv4u4:~/test$ ls -l allfiles.tx*
-rw-rw-r-- 1 paul paul 8813553 Feb 27 05:38 allfiles.txt
paul@RHELv4u4:~/test$
In general, gzip is much faster than bzip2, but the latter one compresses a lot better. Let us
compare the two.
paul@RHELv4u4:~/test$ cp allfiles.txt bllfiles.txt
paul@RHELv4u4:~/test$ time gzip allfiles.txt
real 0m0.050s
user 0m0.041s
sys 0m0.009s
paul@RHELv4u4:~/test$ time bzip2 bllfiles.txt
real 0m5.968s
user 0m5.794s
sys 0m0.076s
paul@RHELv4u4:~/test$ ls -l ?llfiles.tx*
-rw-rw-r-- 1 paul paul 931863 Feb 27 05:38 allfiles.txt.gz
-rw-rw-r-- 1 paul paul 708871 May 12 10:52 bllfiles.txt.bz2
paul@RHELv4u4:~/test$
15.3. tar
The tar utility gets its name from Tape ARchive. This tool will receive and send files to
a destination (typically a tape or a regular file). The c option is used to create a tar archive
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backup
(or tarfile), the f option to name/create the tarfile. The example below takes a backup of /
etc into the file /backup/etc.tar .
root@RHELv4u4:~# tar cf /backup/etc.tar /etc
root@RHELv4u4:~# ls -l /backup/etc.tar
-rw-r--r-- 1 root root 47800320 May 12 11:47 /backup/etc.tar
root@RHELv4u4:~#
Compression can be achieved without pipes since tar uses the z flag to compress with gzip,
and the j flag to compress with bzip2.
root@RHELv4u4:~# tar czf /backup/etc.tar.gz /etc
root@RHELv4u4:~# tar cjf /backup/etc.tar.bz2 /etc
root@RHELv4u4:~# ls -l /backup/etc.ta*
-rw-r--r-- 1 root root 47800320 May 12 11:47 /backup/etc.tar
-rw-r--r-- 1 root root 6077340 May 12 11:48 /backup/etc.tar.bz2
-rw-r--r-- 1 root root 8496607 May 12 11:47 /backup/etc.tar.gz
root@RHELv4u4:~#
The t option is used to list the contents of a tar file. Verbose mode is enabled with v (also
useful when you want to see the files being archived during archiving).
root@RHELv4u4:~# tar tvf /backup/etc.tar
drwxr-xr-x root/root 0 2007-05-12 09:38:21 etc/
-rw-r--r-- root/root 2657 2004-09-27 10:15:03 etc/warnquota.conf
-rw-r--r-- root/root 13136 2006-11-03 17:34:50 etc/mime.types
drwxr-xr-x root/root 0 2004-11-03 13:35:50 etc/sound/
...
To list a specific file in a tar archive, use the t option, added with the filename (without
leading /).
root@RHELv4u4:~# tar tvf /backup/etc.tar etc/resolv.conf
-rw-r--r-- root/root 77 2007-05-12 08:31:32 etc/resolv.conf
root@RHELv4u4:~#
Use the x flag to restore a tar archive, or a single file from the archive. Remember that by
default tar will restore the file in the current directory.
root@RHELv4u4:~# tar xvf /backup/etc.tar etc/resolv.conf
etc/resolv.conf
root@RHELv4u4:~# ls -l /etc/resolv.conf
-rw-r--r-- 2 root root 40 May 12 12:05 /etc/resolv.conf
root@RHELv4u4:~# ls -l etc/resolv.conf
-rw-r--r-- 1 root root 77 May 12 08:31 etc/resolv.conf
root@RHELv4u4:~#
You can preserve file permissions with the p flag. And you can exclude directories or file
with --exclude.
root ~# tar cpzf /backup/etc_with_perms.tgz /etc
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backup
root ~# tar cpzf /backup/etc_no_sysconf.tgz /etc --exclude /etc/sysconfig
root ~# ls -l /backup/etc_*
-rw-r--r-- 1 root root 8434293 May 12 12:48 /backup/etc_no_sysconf.tgz
-rw-r--r-- 1 root root 8496591 May 12 12:48 /backup/etc_with_perms.tgz
root ~#
You can also create a text file with names of files and directories to archive, and then supply
this file to tar with the -T flag.
root@RHELv4u4:~# find /etc -name *.conf > files_to_archive.txt
root@RHELv4u4:~# find /home -name *.pdf >> files_to_archive.txt
root@RHELv4u4:~# tar cpzf /backup/backup.tgz -T files_to_archive.txt
The tar utility can receive filenames from the find command, with the help of xargs.
find /etc -type f -name "*.conf" | xargs tar czf /backup/confs.tar.gz
You can also use tar to copy a directory, this is more efficient than using cp -r.
(cd /etc; tar -cf - . ) | (cd /backup/copy_of_etc/; tar -xpf - )
Another example of tar, this copies a directory securely over the network.
(cd /etc;tar -cf - . )|(ssh user@srv 'cd /backup/cp_of_etc/; tar -xf - ')
tar can be used together with gzip and copy a file to a remote server through ssh
cat backup.tar | gzip | ssh bashuser@192.168.1.105 "cat - > backup.tgz"
Compress the tar backup when it is on the network, but leave it uncompressed at the
destination.
cat backup.tar | gzip | ssh user@192.168.1.105 "gunzip|cat - > backup.tar"
Same as the previous, but let ssh handle the compression
cat backup.tar | ssh -C bashuser@192.168.1.105 "cat - > backup.tar"
15.4. Backup Types
Linux uses multilevel incremental backups using distinct levels. A full backup is a backup
at level 0. A higher level x backup will include all changes since the last level x-1 backup.
Suppose you take a full backup on Monday (level 0) and a level 1 backup on Tuesday, then
the Tuesday backup will contain all changes since Monday. Taking a level 2 on Wednesday
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backup
will contain all changes since Tuesday (the last level 2-1). A level 3 backup on Thursday
will contain all changes since Wednesday (the last level 3-1). Another level 3 on Friday
will also contain all changes since Wednesday. A level 2 backup on Saturday would take
all changes since the last level 1 from Tuesday.
15.5. dump and restore
While dump is similar to tar, it is also very different because it looks at the file system.
Where tar receives a lists of files to backup, dump will find files to backup by itself by
examining ext2. Files found by dump will be copied to a tape or regular file. In case the
target is not big enough to hold the dump (end-of-media), it is broken into multiple volumes.
Restoring files that were backed up with dump is done with the restore command. In the
example below we take a full level 0 backup of two partitions to a SCSI tape. The no rewind
is mandatory to put the volumes behind each other on the tape.
dump 0f /dev/nst0 /boot
dump 0f /dev/nst0 /
Listing files in a dump archive is done with dump -t, and you can compare files with dump
-C.
You can omit files from a dump by changing the dump attribute with the chattr command.
The d attribute on ext will tell dump to skip the file, even during a full backup. In the
following example, /etc/hosts is excluded from dump archives.
chattr +d /etc/hosts
To restore the complete file system with restore, use the -r option. This can be useful to
change the size or block size of a file system. You should have a clean file system mounted
and cd'd into it. Like this example shows.
mke2fs /dev/hda3
mount /dev/hda3 /mnt/data
cd /mnt/data
restore rf /dev/nst0
To extract only one file or directory from a dump, use the -x option.
restore -xf /dev/st0 /etc
15.6. cpio
Different from tar and dump is cpio (Copy Input and Output). It can be used to receive
filenames, but copies the actual files. This makes it an easy companion with find! Some
examples below.
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backup
find sends filenames to cpio, which puts the files in an archive.
find /etc -depth -print | cpio -oaV -O archive.cpio
The same, but compressed with gzip
find /etc -depth -print | cpio -oaV | gzip -c > archive.cpio.gz
Now pipe it through ssh (backup files to a compressed file on another machine)
find /etc -depth -print|cpio -oaV|gzip -c|ssh server "cat - > etc.cpio.gz"
find sends filenames to cpio | cpio sends files to ssh | ssh sends files to cpio 'cpio extracts files'
find /etc -depth -print | cpio -oaV | ssh user@host 'cpio -imVd'
the same but reversed: copy a dir from the remote host to the local machine
ssh user@host "find path -depth -print | cpio -oaV" | cpio -imVd
15.7. dd
15.7.1. About dd
Some people use dd to create backups. This can be very powerful, but dd backups can only
be restored to very similar partitions or devices. There are however a lot of useful things
possible with dd. Some examples.
15.7.2. Create a CDROM image
The easiest way to create a .ISO file from any CD. The if switch means Input File, of is the
Output File. Any good tool can burn a copy of the CD with this .ISO file.
dd if=/dev/cdrom of=/path/to/cdrom.ISO
15.7.3. Create a floppy image
A little outdated maybe, but just in case : make an image file from a 1.44MB floppy.
Blocksize is defined by bs, and count contains the number of blocks to copy.
dd if=/dev/floppy of=/path/to/floppy.img bs=1024 count=1440
15.7.4. Copy the master boot record
Use dd to copy the MBR (Master Boot Record) of hard disk /dev/hda to a file.
dd if=/dev/hda of=/MBR.img bs=512 count=1
15.7.5. Copy files
This example shows how dd can copy files. Copy the file summer.txt to
copy_of_summer.txt .
dd if=~/summer.txt of=~/copy_of_summer.txt
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15.7.6. Image disks or partitions
And who needs ghost when dd can create a (compressed) image of a partition.
dd if=/dev/hdb2 of=/image_of_hdb2.IMG
dd if=/dev/hdb2 | gzip > /image_of_hdb2.IMG.gz
15.7.7. Create files of a certain size
dd can be used to create a file of any size. The first example creates a one MEBIbyte file,
the second a one MEGAbyte file.
dd if=/dev/zero of=file1MB count=1024 bs=1024
dd if=/dev/zero of=file1MB count=1000 bs=1024
15.7.8. CDROM server example
And there are of course endless combinations with ssh and bzip2. This example puts a bzip2
backup of a cdrom on a remote server.
dd if=/dev/cdrom |bzip2|ssh user@host "cat - > /backups/cd/cdrom.iso.bz2"
15.8. split
The split command is useful to split files into smaller files. This can be useful to fit the file
onto multiple instances of a medium too small to contain the complete file. In the example
below, a file of size 5000 bytes is split into three smaller files, with maximum 2000 bytes
each.
paul@laika:~/test$ ls -l
total 8
-rw-r--r-- 1 paul paul 5000 2007-09-09 20:46 bigfile1
paul@laika:~/test$ split -b 2000 bigfile1 splitfile.
paul@laika:~/test$ ls -l
total 20
-rw-r--r-- 1 paul paul 5000 2007-09-09 20:46 bigfile1
-rw-r--r-- 1 paul paul 2000 2007-09-09 20:47 splitfile.aa
-rw-r--r-- 1 paul paul 2000 2007-09-09 20:47 splitfile.ab
-rw-r--r-- 1 paul paul 1000 2007-09-09 20:47 splitfile.ac
15.9. practice: backup
!! Careful with tar options and the position of the backup file, mistakes can destroy your
system!!
1. Create a directory (or partition if you like) for backups. Link (or mount) it under /mnt/
backup.
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2a. Use tar to backup /etc in /mnt/backup/etc_date.tgz, the backup must be gzipped. (Replace
date with the current date)
2b. Use tar to backup /bin to /mnt/backup/bin_date.tar.bz2, the backup must be bzip2'd.
2c. Choose a file in /etc and /bin and verify with tar that the file is indeed backed up.
2d. Extract those two files to your home directory.
3a. Create a backup directory for your neighbour, make it accessible under /mnt/
neighbourName
3b. Combine ssh and tar to put a backup of your /boot on your neighbours computer in /
mnt/YourName
4a. Combine find and cpio to create a cpio archive of /etc.
4b. Choose a file in /etc and restore it from the cpio archive into your home directory.
5. Use dd and ssh to put a backup of the master boot record on your neighbours computer.
6. (On the real computer) Create and mount an ISO image of the ubuntu cdrom.
7. Combine dd and gzip to create a 'ghost' image of one of your partitions on another partition.
8. Use dd to create a five megabyte file in ~/testsplit and name it biggest. Then split this file
in smaller two megabyte parts.
mkdir testsplit
dd if=/dev/zero of=~/testsplit/biggest count=5000 bs=1024
split -b 2000000 biggest parts
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Part IV. mysql database
Table of Contents
16. introduction to sql using mysql .......................................................................................................... 171
16.1. installing mysql ......................................................................................................................... 172
16.2. accessing mysql ......................................................................................................................... 173
16.3. mysql databases ......................................................................................................................... 175
16.4. mysql tables .............................................................................................................................. 177
16.5. mysql records ............................................................................................................................ 179
16.6. joining two tables ...................................................................................................................... 182
16.7. mysql triggers ............................................................................................................................ 183
170
Chapter 16. introduction to sql using
mysql
mysql is a database server that understands Structured Query Language (SQL). MySQL
was developed by the Swedish Company MySQL AB. The first release was in 1995. In
2008 MySQL AB was bought by Sun Microsystems (which is now owned by Oracle).
mysql is very popular for websites in combination with php and apache (the m in lamp
servers), but mysql is also used in organizations with huge databases like Facebook, Flickr,
Google, Nokia, Wikipedia and Youtube.
This chapter will teach you sql by creating and using small databases, tables, queries and a
simple trigger in a local mysql server.
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introduction to sql using mysql
16.1. installing mysql
On Debian/Ubuntu you can use aptitude install mysql-server to install the mysql server
and client.
root@ubu1204~# aptitude install mysql-server
The following NEW packages will be installed:
libdbd-mysql-perl{a} libdbi-perl{a} libhtml-template-perl{a}
libnet-daemon-perl{a} libplrpc-perl{a} mysql-client-5.5{a}
mysql-client-core-5.5{a} mysql-server mysql-server-5.5{a}
mysql-server-core-5.5{a}
0 packages upgraded, 10 newly installed, 0 to remove and 1 not upgraded.
Need to get 25.5 MB of archives. After unpacking 88.4 MB will be used.
Do you want to continue? [Y/n/?]
During the installation you will be asked to provide a password for the root mysql user,
remember this password (or use hunter2 like i do.
To verify the installed version, use dpkg -l on Debian/Ubuntu. This screenshot shows
version 5.0 installed.
root@ubu1204~# dpkg -l mysql-server | tail -1 | tr -s ' ' | cut -c-72
ii mysql-server 5.5.24-0ubuntu0.12.04.1 MySQL database server (metapacka
Issue rpm -q to get version information about MySQL on Red Hat/Fedora/CentOS.
[paul@RHEL52 ~]$ rpm -q mysql-server
mysql-server-5.0.45-7.el5
You will need at least version 5.0 to work with triggers.
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introduction to sql using mysql
16.2. accessing mysql
16.2.1. Linux users
The installation of mysql creates a user account in /etc/passwd and a group account in /
etc/group.
kevin@ubu1204:~$ tail -1 /etc/passwd
mysql:x:120:131:MySQL Server,,,:/nonexistent:/bin/false
kevin@ubu1204:~$ tail -1 /etc/group
mysql:x:131:
The mysql daemon mysqld will run with the credentials of this user and group.
root@ubu1204~# ps -eo uid,user,gid,group,comm | grep mysqld
120 mysql 131 mysql mysqld
16.2.2. mysql client application
You can now use mysql from the commandline by just typing mysql -u root -p and you
'll be asked for the password (of the mysql root account). In the screenshot below the user
typed exit to exit the mysql console.
root@ubu1204~# mysql -u root -p
Enter password:
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 43
Server version: 5.5.24-0ubuntu0.12.04.1 (Ubuntu)
Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> exit
Bye
You could also put the password in clear text on the command line, but that would not be
very secure. Anyone with access to your bash history would be able to read your mysql root
password.
root@ubu1204~# mysql -u root -phunter2
Welcome to the MySQL monitor. Commands end with ; or \g.
...
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16.2.3. ~/.my.cnf
You can save configuration in your home directory in the hidden file .my.cnf. In the
screenshot below we put the root user and password in .my.cnf.
kevin@ubu1204:~$ pwd
/home/kevin
kevin@ubu1204:~$ cat .my.cnf
[client]
user=root
password=hunter2
kevin@ubu1204:~$
This enables us to log on as the root mysql user just by typing mysql.
kevin@ubu1204:~$ mysql
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 56
Server version: 5.5.24-0ubuntu0.12.04.1 (Ubuntu)
16.2.4. the mysql command line client
You can use the mysql command to take a look at the databases, and to execute SQL queries
on them. The screenshots below show you how.
Here we execute the command show databases. Every command must be terminated by a
delimiter. The default delimiter is ; (the semicolon).
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| test |
+--------------------+
4 rows in set (0.00 sec)
We will use this prompt in the next sections.
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16.3. mysql databases
16.3.1. listing all databases
You can use the mysql command to take a look at the databases, and to execute SQL queries
on them. The screenshots below show you how. First, we log on to our MySQL server and
execute the command show databases to see which databases exist on our mysql server.
kevin@ubu1204:~$ mysql
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 57
Server version: 5.5.24-0ubuntu0.12.04.1 (Ubuntu)
Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.
Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| performance_schema |
| test |
+--------------------+
4 rows in set (0.00 sec)
16.3.2. creating a database
You can create a new database with the create database command.
mysql> create database famouspeople;
Query OK, 1 row affected (0.00 sec)
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| famouspeople |
| mysql |
| performance_schema |
| test |
+--------------------+
5 rows in set (0.00 sec)
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16.3.3. using a database
Next we tell mysql to use one particular database with the use $database command. This
screenshot shows how to make wikidb the current database (in use).
mysql> use famouspeople;
Database changed
mysql>
16.3.4. access to a database
To give someone access to a mysql database, use the grant command.
mysql> grant all on famouspeople.* to kevin@localhost IDENTIFIED BY "hunter2";
Query OK, 0 rows affected (0.00 sec)
16.3.5. deleting a database
When a database is no longer needed, you can permanently remove it with the drop database
command.
mysql> drop database demodb;
Query OK, 1 row affected (0.09 sec)
16.3.6. backup and restore a database
You can take a backup of a database, or move it to another computer using the mysql and
mysqldump commands. In the screenshot below, we take a backup of the wikidb database
on the computer named laika.
mysqldump -u root famouspeople > famouspeople.backup.20120708.sql
Here is a screenshot of a database restore operation from this backup.
mysql -u root famouspeople < famouspeople.backup.20120708.sql
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16.4. mysql tables
16.4.1. listing tables
You can see a list of tables in the current database with the show tables; command. Our
famouspeople database has no tables yet.
mysql> use famouspeople;
Database changed
mysql> show tables;
Empty set (0.00 sec)
16.4.2. creating a table
The create table command will create a new table.
This screenshot shows the creation of a country table. We use the countrycode as a primary
key (all country codes are uniquely defined). Most country codes are two or three letters, so
a char of three uses less space than a varchar of three. The country name and the name of
the capital are both defined as varchar. The population can be seen as an integer.
mysql> create table country (
-> countrycode char(3) NOT NULL,
-> countryname varchar(70) NOT NULL,
-> population int,
-> countrycapital varchar(50),
-> primary key (countrycode)
-> );
Query OK, 0 rows affected (0.19 sec)
mysql> show tables;
+------------------------+
| Tables_in_famouspeople |
+------------------------+
| country |
+------------------------+
1 row in set (0.00 sec)
mysql>
You are allowed to type the create table command on one long line, but administrators often
use multiple lines to improve readability.
mysql> create table country ( countrycode char(3) NOT NULL, countryname\
varchar(70) NOT NULL, population int, countrycapital varchar(50), prim\
ary key (countrycode) );
Query OK, 0 rows affected (0.18 sec)
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16.4.3. describing a table
To see a description of the structure of a table, issue the describe $tablename command
as shown below.
mysql> describe country;
+----------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+----------------+-------------+------+-----+---------+-------+
| countrycode | char(3) | NO | PRI | NULL | |
| countryname | varchar(70) | NO | | NULL | |
| population | int(11) | YES | | NULL | |
| countrycapital | varchar(50) | YES | | NULL | |
+----------------+-------------+------+-----+---------+-------+
4 rows in set (0.00 sec)
16.4.4. removing a table
To remove a table from a database, issue the drop table $tablename command as shown
below.
mysql> drop table country;
Query OK, 0 rows affected (0.00 sec)
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16.5. mysql records
16.5.1. creating records
Use insert to enter data into the table. The screenshot shows several insert statements that
insert values depending on the position of the data in the statement.
mysql> insert into country values ('BE','Belgium','11000000','Brussels');
Query OK, 1 row affected (0.05 sec)
mysql> insert into country values ('DE','Germany','82000000','Berlin');
Query OK, 1 row affected (0.05 sec)
mysql> insert into country values ('JP','Japan','128000000','Tokyo');
Query OK, 1 row affected (0.05 sec)
Some administrators prefer to use uppercase for sql keywords. The mysql client accepts
both.
mysql> INSERT INTO country VALUES ('FR','France','64000000','Paris');
Query OK, 1 row affected (0.00 sec)
Note that you get an error when using a duplicate primary key.
mysql> insert into country values ('DE','Germany','82000000','Berlin');
ERROR 1062 (23000): Duplicate entry 'DE' for key 'PRIMARY'
16.5.2. viewing all records
Below an example of a simple select query to look at the contents of a table.
mysql> select * from country;
+-------------+---------------+------------+----------------+
| countrycode | countryname | population | countrycapital |
+-------------+---------------+------------+----------------+
| BE | Belgium | 11000000 | Brussels |
| CN | China | 1400000000 | Beijing |
| DE | Germany | 82000000 | Berlin |
| FR | France | 64000000 | Paris |
| IN | India | 1300000000 | New Delhi |
| JP | Japan | 128000000 | Tokyo |
| MX | Mexico | 113000000 | Mexico City |
| US | United States | 313000000 | Washington |
+-------------+---------------+------------+----------------+
8 rows in set (0.00 sec)
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16.5.3. updating records
Consider the following insert statement. The capital of Spain is not Barcelona, it is Madrid.
mysql> insert into country values ('ES','Spain','48000000','Barcelona');
Query OK, 1 row affected (0.08 sec)
Using an update statement, the record can be updated.
mysql> update country set countrycapital='Madrid' where countrycode='ES';
Query OK, 1 row affected (0.07 sec)
Rows matched: 1 Changed: 1 Warnings: 0
We can use a select statement to verify this change.
mysql> select * from country;
+-------------+---------------+------------+----------------+
| countrycode | countryname | population | countrycapital |
+-------------+---------------+------------+----------------+
| BE | Belgium | 11000000 | Brussels |
| CN | China | 1400000000 | Beijing |
| DE | Germany | 82000000 | Berlin |
| ES | Spain | 48000000 | Madrid |
| FR | France | 64000000 | Paris |
| IN | India | 1300000000 | New Delhi |
| JP | Japan | 128000000 | Tokyo |
| MX | Mexico | 113000000 | Mexico City |
| US | United States | 313000000 | Washington |
+-------------+---------------+------------+----------------+
9 rows in set (0.00 sec)
16.5.4. viewing selected records
Using a where clause in a select statement, you can specify which record(s) you want to see.
mysql> SELECT * FROM country WHERE countrycode='ES';
+-------------+-------------+------------+----------------+
| countrycode | countryname | population | countrycapital |
+-------------+-------------+------------+----------------+
| ES | Spain | 48000000 | Madrid |
+-------------+-------------+------------+----------------+
1 row in set (0.00 sec)
Another example of the where clause.
mysql> select * from country where countryname='Spain';
+-------------+-------------+------------+----------------+
| countrycode | countryname | population | countrycapital |
+-------------+-------------+------------+----------------+
| ES | Spain | 48000000 | Madrid |
+-------------+-------------+------------+----------------+
1 row in set (0.00 sec)
16.5.5. primary key in where clause ?
The primary key of a table is a field that uniquely identifies every record (every row) in
the table. when using another field in the where clause, it is possible to get multiple rows
returned.
mysql> insert into country values ('EG','Egypt','82000000','Cairo');
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Query OK, 1 row affected (0.33 sec)
mysql> select * from country where population='82000000';
+-------------+-------------+------------+----------------+
| countrycode | countryname | population | countrycapital |
+-------------+-------------+------------+----------------+
| DE | Germany | 82000000 | Berlin |
| EG | Egypt | 82000000 | Cairo |
+-------------+-------------+------------+----------------+
2 rows in set (0.00 sec)
16.5.6. ordering records
We know that select allows us to see all records in a table. Consider this table.
mysql> select countryname,population from country;
+---------------+------------+
| countryname | population |
+---------------+------------+
| Belgium | 11000000 |
| China | 1400000000 |
| Germany | 82000000 |
| Egypt | 82000000 |
| Spain | 48000000 |
| France | 64000000 |
| India | 1300000000 |
| Japan | 128000000 |
| Mexico | 113000000 |
| United States | 313000000 |
+---------------+------------+
10 rows in set (0.00 sec)
Using the order by clause, we can change the order in which the records are presented.
mysql> select countryname,population from country order by countryname;
+---------------+------------+
| countryname | population |
+---------------+------------+
| Belgium | 11000000 |
| China | 1400000000 |
| Egypt | 82000000 |
| France | 64000000 |
| Germany | 82000000 |
| India | 1300000000 |
| Japan | 128000000 |
| Mexico | 113000000 |
| Spain | 48000000 |
| United States | 313000000 |
+---------------+------------+
10 rows in set (0.00 sec)
16.5.7. grouping records
Consider this table of people. The screenshot shows how to use the avg function to calculate
an average.
mysql> select * from people;
+-----------------+-----------+-----------+-------------+
| Name | Field | birthyear | countrycode |
+-----------------+-----------+-----------+-------------+
| Barack Obama | politics | 1961 | US |
| Deng Xiaoping | politics | 1904 | CN |
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| Guy Verhofstadt | politics | 1953 | BE |
| Justine Henin | tennis | 1982 | BE |
| Kim Clijsters | tennis | 1983 | BE |
| Li Na | tennis | 1982 | CN |
| Liu Yang | astronaut | 1978 | CN |
| Serena Williams | tennis | 1981 | US |
| Venus Williams | tennis | 1980 | US |
+-----------------+-----------+-----------+-------------+
9 rows in set (0.00 sec)
mysql> select Field,AVG(birthyear) from people;
+----------+-------------------+
| Field | AVG(birthyear) |
+----------+-------------------+
| politics | 1967.111111111111 |
+----------+-------------------+
1 row in set (0.00 sec)
Using the group by clause, we can have an average per field.
mysql> select Field,AVG(birthyear) from people group by Field;
+-----------+--------------------+
| Field | AVG(birthyear) |
+-----------+--------------------+
| astronaut | 1978 |
| politics | 1939.3333333333333 |
| tennis | 1981.6 |
+-----------+--------------------+
3 rows in set (0.00 sec)
16.5.8. deleting records
You can use the delete to permanently remove a record from a table.
mysql> delete from country where countryname='Spain';
Query OK, 1 row affected (0.06 sec)
mysql> select * from country where countryname='Spain';
Empty set (0.00 sec)
16.6. joining two tables
16.6.1. inner join
With an inner join you can take values from two tables and combine them in one result.
Consider the country and the people tables from the previous section when looking at this
screenshot of an inner join.
mysql> select Name,Field,countryname
-> from country
-> inner join people on people.countrycode=country.countrycode;
+-----------------+-----------+---------------+
| Name | Field | countryname |
+-----------------+-----------+---------------+
| Barack Obama | politics | United States |
| Deng Xiaoping | politics | China |
| Guy Verhofstadt | politics | Belgium |
| Justine Henin | tennis | Belgium |
| Kim Clijsters | tennis | Belgium |
| Li Na | tennis | China |
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| Liu Yang | astronaut | China |
| Serena Williams | tennis | United States |
| Venus Williams | tennis | United States |
+-----------------+-----------+---------------+
9 rows in set (0.00 sec)
This inner join will show only records with a match on countrycode in both tables.
16.6.2. left join
A left join is different from an inner join in that it will take all rows from the left table,
regardless of a match in the right table.
mysql> select Name,Field,countryname from country left join people on people.countrycode=countr
+-----------------+-----------+---------------+
| Name | Field | countryname |
+-----------------+-----------+---------------+
| Guy Verhofstadt | politics | Belgium |
| Justine Henin | tennis | Belgium |
| Kim Clijsters | tennis | Belgium |
| Deng Xiaoping | politics | China |
| Li Na | tennis | China |
| Liu Yang | astronaut | China |
| NULL | NULL | Germany |
| NULL | NULL | Egypt |
| NULL | NULL | Spain |
| NULL | NULL | France |
| NULL | NULL | India |
| NULL | NULL | Japan |
| NULL | NULL | Mexico |
| Barack Obama | politics | United States |
| Serena Williams | tennis | United States |
| Venus Williams | tennis | United States |
+-----------------+-----------+---------------+
16 rows in set (0.00 sec)
You can see that some countries are present, even when they have no matching records in
the people table.
16.7. mysql triggers
16.7.1. using a before trigger
Consider the following create table command. The last field (amount) is the multiplication
of the two fields named unitprice and unitcount.
mysql> create table invoices (
-> id char(8) NOT NULL,
-> customerid char(3) NOT NULL,
-> unitprice int,
-> unitcount smallint,
-> amount int );
Query OK, 0 rows affected (0.00 sec)
We can let mysql do the calculation for that by using a before trigger. The screenshot below
shows the creation of a trigger that calculates the amount by multiplying two fields that are
about to be inserted.
mysql> create trigger total_amount before INSERT on invoices
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-> for each row set new.amount = new.unitprice * new.unitcount ;
Query OK, 0 rows affected (0.02 sec)
Here we verify that the trigger works by inserting a new record, without providing the total
amount.
mysql> insert into invoices values ('20090526','ABC','199','10','');
Query OK, 1 row affected (0.02 sec)
Looking at the record proves that the trigger works.
mysql> select * from invoices;
+----------+------------+-----------+-----------+--------+
| id | customerid | unitprice | unitcount | amount |
+----------+------------+-----------+-----------+--------+
| 20090526 | ABC | 199 | 10 | 1990 |
+----------+------------+-----------+-----------+--------+
1 row in set (0.00 sec)
16.7.2. removing a trigger
When a trigger is no longer needed, you can delete it with the drop trigger command.
mysql> drop trigger total_amount;
Query OK, 0 rows affected (0.00 sec)
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Part V. Introduction to Samba
Table of Contents
17. introduction to samba ......................................................................................................................... 188
17.1. verify installed version ............................................................................................................. 189
17.2. installing samba ......................................................................................................................... 190
17.3. documentation ........................................................................................................................... 191
17.4. starting and stopping samba ..................................................................................................... 192
17.5. samba daemons ......................................................................................................................... 193
17.6. the SMB protocol ...................................................................................................................... 194
17.7. practice: introduction to samba ................................................................................................. 195
18. getting started with samba ................................................................................................................. 196
18.1. /etc/samba/smb.conf .................................................................................................................. 197
18.2. /usr/bin/testparm ........................................................................................................................ 198
18.3. /usr/bin/smbclient ....................................................................................................................... 199
18.4. /usr/bin/smbtree ......................................................................................................................... 201
18.5. server string ............................................................................................................................... 202
18.6. Samba Web Administration Tool (SWAT) .............................................................................. 203
18.7. practice: getting started with samba ......................................................................................... 204
18.8. solution: getting started with samba ......................................................................................... 205
19. a read only file server ......................................................................................................................... 207
19.1. Setting up a directory to share ................................................................................................. 208
19.2. configure the share .................................................................................................................... 208
19.3. restart the server ........................................................................................................................ 209
19.4. verify the share ......................................................................................................................... 209
19.5. a note on netcat ......................................................................................................................... 211
19.6. practice: read only file server ................................................................................................... 212
19.7. solution: read only file server ................................................................................................... 213
20. a writable file server ........................................................................................................................... 214
20.1. set up a directory to share ........................................................................................................ 215
20.2. share section in smb.conf ......................................................................................................... 215
20.3. configure the share .................................................................................................................... 215
20.4. test connection with windows .................................................................................................. 215
20.5. test writing with windows ........................................................................................................ 216
20.6. How is this possible ? ............................................................................................................... 216
20.7. practice: writable file server ..................................................................................................... 217
20.8. solution: writable file server ..................................................................................................... 218
21. samba first user account ..................................................................................................................... 219
21.1. creating a samba user ............................................................................................................... 220
21.2. ownership of files ..................................................................................................................... 220
21.3. /usr/bin/smbpasswd .................................................................................................................... 220
21.4. /etc/samba/smbpasswd ............................................................................................................... 220
21.5. passdb backend ......................................................................................................................... 221
21.6. forcing this user ........................................................................................................................ 221
21.7. practice: first samba user account ............................................................................................ 222
21.8. solution: first samba user account ............................................................................................ 223
22. samba authentication .......................................................................................................................... 224
22.1. creating the users on Linux ...................................................................................................... 225
22.2. creating the users on samba ...................................................................................................... 225
22.3. security = user ........................................................................................................................... 225
22.4. configuring the share ................................................................................................................ 226
22.5. testing access with net use ........................................................................................................ 226
22.6. testing access with smbclient .................................................................................................... 226
22.7. verify ownership ....................................................................................................................... 227
22.8. common problems ..................................................................................................................... 227
22.9. practice : samba authentication ................................................................................................. 229
22.10. solution: samba authentication ................................................................................................ 230
23. samba securing shares ........................................................................................................................ 231
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23.1. security based on user name ..................................................................................................... 232
23.2. security based on ip-address ..................................................................................................... 232
23.3. security through obscurity ........................................................................................................ 233
23.4. file system security ................................................................................................................... 233
23.5. practice: securing shares ........................................................................................................... 235
23.6. solution: securing shares ........................................................................................................... 236
24. samba domain member ....................................................................................................................... 238
24.1. changes in smb.conf .................................................................................................................. 239
24.2. joining an Active Directory domain ......................................................................................... 240
24.3. winbind ...................................................................................................................................... 241
24.4. wbinfo ........................................................................................................................................ 241
24.5. getent ......................................................................................................................................... 242
24.6. file ownership ............................................................................................................................ 243
24.7. practice : samba domain member ............................................................................................. 244
25. samba domain controller .................................................................................................................... 245
25.1. about Domain Controllers ......................................................................................................... 246
25.2. About security modes ............................................................................................................... 246
25.3. About password backends ........................................................................................................ 247
25.4. [global] section in smb.conf ..................................................................................................... 247
25.5. netlogon share ........................................................................................................................... 248
25.6. other [share] sections ................................................................................................................ 248
25.7. Users and Groups ...................................................................................................................... 249
25.8. tdbsam ....................................................................................................................................... 249
25.9. about computer accounts .......................................................................................................... 250
25.10. local or roaming profiles ........................................................................................................ 250
25.11. Groups in NTFS acls .............................................................................................................. 251
25.12. logon scripts ............................................................................................................................ 252
25.13. practice: samba domain controller .......................................................................................... 253
26. a brief look at samba 4 ....................................................................................................................... 254
26.1. Samba 4 alpha 6 ....................................................................................................................... 256
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Chapter 17. introduction to samba
This introduction to the Samba server simply explains how to install Samba 3 and briefly
mentions the SMB protocol.
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17.1. verify installed version
17.1.1. .rpm based distributions
To see the version of samba installed on Red Hat, Fedora or CentOS use rpm -q samba.
[root@RHEL52 ~]# rpm -q samba
samba-3.0.28-1.el5_2.1
The screenshot above shows that RHEL5 has Samba version 3.0 installed. The last number
in the Samba version counts the number of updates or patches.
Below the same command on a more recent version of CentOS with Samba version 3.5
installed.
[root@centos6 ~]# rpm -q samba
samba-3.5.10-116.el6_2.i686
17.1.2. .deb based distributions
Use dpkg -l or aptitide show on Debian or Ubuntu. Both Debian 7.0 (Wheezy) and Ubuntu
12.04 (Precise) use version 3.6.3 of the Samba server.
root@debian7~# aptitude show samba | grep Version
Version: 2:3.6.3-1
Ubuntu 12.04 is currently at Samba version 3.6.3.
root@ubu1204:~# dpkg -l samba | tail -1
ii samba 2:3.6.3-2ubuntu2.1 SMB/CIFS file, print, and login server for Unix
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17.2. installing samba
17.2.1. .rpm based distributions
Samba is installed by default on Red Hat Enterprise Linux. If Samba is not yet installed,
then you can use the graphical menu (Applications -- System Settings -- Add/Remove
Applications) and select "Windows File Server" in the Server section. The non-graphical
way is to use rpm or yum.
When you downloaded the .rpm file, you can install Samba like this.
[paul@RHEL52 ~]$ rpm -i samba-3.0.28-1.el5_2.1.rpm
When you have a subscription to RHN (Red Hat Network), then yum is an easy tool to use.
This yum command works by default on Fedora and CentOS.
[root@centos6 ~]# yum install samba
17.2.2. .deb based distributions
Ubuntu and Debian users can use the aptitude program (or use a graphical tool like
Synaptic).
root@debian7~# aptitude install samba
The following NEW packages will be installed:
samba samba-common{a} samba-common-bin{a} tdb-tools{a}
0 packages upgraded, 4 newly installed, 0 to remove and 1 not upgraded.
Need to get 15.1 MB of archives. After unpacking 42.9 MB will be used.
Do you want to continue? [Y/n/?]
...
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17.3. documentation
17.3.1. samba howto
Samba comes with excellent documentation in html and pdf format (and also as a free
download from samba.org and it is for sale as a printed book).
The documentation is a separate package, so install it if you want it on the server itself.
[root@centos6 ~]# yum install samba-doc
...
[root@centos6 ~]# ls -l /usr/share/doc/samba-doc-3.5.10/
total 10916
drwxr-xr-x. 6 root root 4096 May 6 15:50 htmldocs
-rw-r--r--. 1 root root 4605496 Jun 14 2011 Samba3-ByExample.pdf
-rw-r--r--. 1 root root 608260 Jun 14 2011 Samba3-Developers-Guide.pdf
-rw-r--r--. 1 root root 5954602 Jun 14 2011 Samba3-HOWTO.pdf
This action is very similar on Ubuntu and Debian except that the pdf files are in a separate
package named samba-doc-pdf.
root@ubu1204:~# aptitude install samba-doc-pdf
The following NEW packages will be installed:
samba-doc-pdf
...
17.3.2. samba by example
Besides the howto, there is also an excellent book called Samba By Example (again
available as printed edition in shops, and as a free pdf and html).
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17.4. starting and stopping samba
You can start the daemons by invoking /etc/init.d/smb start (some systems use /etc/init.d/
samba) on any linux.
root@laika:~# /etc/init.d/samba stop
* Stopping Samba daemons [ OK ]
root@laika:~# /etc/init.d/samba start
* Starting Samba daemons [ OK ]
root@laika:~# /etc/init.d/samba restart
* Stopping Samba daemons [ OK ]
* Starting Samba daemons [ OK ]
root@laika:~# /etc/init.d/samba status
* SMBD is running [ OK ]
Red Hat derived systems are happy with service smb start.
[root@RHEL4b ~]# /etc/init.d/smb start
Starting SMB services: [ OK ]
Starting NMB services: [ OK ]
[root@RHEL4b ~]# service smb restart
Shutting down SMB services: [ OK ]
Shutting down NMB services: [ OK ]
Starting SMB services: [ OK ]
Starting NMB services: [ OK ]
[root@RHEL4b ~]#
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17.5. samba daemons
Samba 3 consists of three daemons, they are named nmbd, smbd and winbindd.
17.5.1. nmbd
The nmbd daemon takes care of all the names and naming. It registers and resolves names,
and handles browsing. According to the Samba documentation, it should be the first daemon
to start.
[root@RHEL52 ~]# ps -C nmbd
PID TTY TIME CMD
5681 ? 00:00:00 nmbd
17.5.2. smbd
The smbd daemon manages file transfers and authentication.
[root@RHEL52 ~]# ps -C smbd
PID TTY TIME CMD
5678 ? 00:00:00 smbd
5683 ? 00:00:00 smbd
17.5.3. winbindd
The winbind daemon (winbindd) is only started to handle Microsoft Windows domain
membership.
Note that winbindd is started by the /etc/init.d/winbind script (two dd's for the daemon and
only one d for the script).
[root@RHEL52 ~]# /etc/init.d/winbind start
Starting Winbind services: [ OK ]
[root@RHEL52 ~]# ps -C winbindd
PID TTY TIME CMD
5752 ? 00:00:00 winbindd
5754 ? 00:00:00 winbindd
On Debian and Ubuntu, the winbindd daemon is installed via a separate package called
winbind.
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17.6. the SMB protocol
17.6.1. brief history
Development of this protocol was started by IBM in the early eighties. By the end of the
eighties, most develpment was done by Microsoft. SMB is an application level protocol
designed to run on top of NetBIOS/NetBEUI, but can also be run on top of tcp/ip.
In 1996 Microsoft was asked to document the protocol. They submitted CIFS (Common
Internet File System) as an internet draft, but it never got final rfc status.
In 2004 the European Union decided Microsoft should document the protocol to enable
other developers to write compatible software. December 20th 2007 Microsoft came to an
agreement. The Samba team now has access to SMB/CIFS, Windows for Workgroups and
Active Directory documentation.
17.6.2. broadcasting protocol
SMB uses the NetBIOS service location protocol, which is a broadcasting protocol. This
means that NetBIOS names have to be unique on the network (even when you have
different IP-addresses). Having duplicate names on an SMB network can seriously harm
communications.
17.6.3. NetBIOS names
NetBIOS names are similar to hostnames, but are always uppercase and only 15 characters
in length. Microsoft Windows computers and Samba servers will broadcast this name on
the network.
17.6.4. network bandwidth
Having many broadcasting SMB/CIFS computers on your network can cause bandwidth
issues. A solution can be the use of a NetBIOS name server (NBNS) like WINS (Windows
Internet Naming Service).
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17.7. practice: introduction to samba
0. !! Make sure you know your student number, anything *ANYTHING* you name must
include your student number!
1. Verify that you can logon to a Linux/Unix computer. Write down the name and ip address
of this computer.
2. Do the same for all the other (virtual) machines available to you.
3. Verify networking by pinging the computer, edit the appropriate hosts files so you can
use names. Test the names by pinging them.
4. Make sure Samba is installed, write down the version of Samba.
5. Open the Official Samba-3 howto pdf file that is installed on your computer. How many
A4 pages is this file ? Then look at the same pdf on samba.org, it is updated regularly.
6. Stop the Samba server.
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Chapter 18. getting started with
samba
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18.1. /etc/samba/smb.conf
18.1.1. smbd -b
Samba configuration is done in the smb.conf file. The file can be edited manually, or you
can use a web based interface like webmin or swat to manage it. The file is usually located
in /etc/samba. You can find the exact location with smbd -b.
[root@RHEL4b ~]# smbd -b | grep CONFIGFILE
CONFIGFILE: /etc/samba/smb.conf
18.1.2. the default smb.conf
The default smb.conf file contains a lot of examples with explanations.
[paul@RHEL4b ~]$ ls -l /etc/samba/smb.conf
-rw-r--r-- 1 root root 10836 May 30 23:08 /etc/samba/smb.conf
Also on Ubuntu and Debian, smb.conf is packed with samples and explanations.
paul@laika:~$ ls -l /etc/samba/smb.conf
-rw-r--r-- 1 root root 10515 2007-05-24 00:21 /etc/samba/smb.conf
18.1.3. minimal smb.conf
Below is an example of a very minimalistic smb.conf. It allows samba to start, and to be
visible to other computers (Microsoft shows computers in Network Neighborhood or My
Network Places).
[paul@RHEL4b ~]$ cat /etc/samba/smb.conf
[global]
workgroup = WORKGROUP
[firstshare]
path = /srv/samba/public
18.1.4. net view
Below is a screenshot of the net view command on Microsoft Windows Server 2003 sp2.
It shows how a Red Hat Enterprise Linux 5.3 and a Ubuntu 9.04 Samba server, both with a
minimalistic smb.conf, are visible to Microsoft computers nearby.
C:\Documents and Settings\Administrator>net view
Server Name Remark
----------------------------------------------------------------------
\\LAIKA Samba 3.3.2
\\RHEL53 Samba 3.0.33-3.7.el5
\\W2003
The command completed successfully.
18.1.5. long lines in smb.conf
Some parameters in smb.conf can get a long list of values behind them. You can continue a
line (for clarity) on the next by ending the line with a backslash.
valid users = Serena, Venus, Lindsay \
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Kim, Justine, Sabine \
Amelie, Marie, Suzanne
18.1.6. curious smb.conf
Curious but true: smb.conf accepts synonyms like create mode and create mask, and
(sometimes) minor spelling errors like browsable and browseable. And on occasion you
can even switch words, the guest only parameter is identical to only guest. And writable
= yes is the same as readonly = no.
18.1.7. man smb.conf
You can access a lot of documentation when typing man smb.conf.
[root@RHEL4b samba]# apropos samba
cupsaddsmb (8) - export printers to samba for windows clients
lmhosts (5) - The Samba NetBIOS hosts file
net (8) - Tool for administration of Samba and remote CIFS servers
pdbedit (8) - manage the SAM database (Database of Samba Users)
samba (7) - A Windows SMB/CIFS fileserver for UNIX
smb.conf [smb] (5) - The configuration file for the Samba suite
smbpasswd (5) - The Samba encrypted password file
smbstatus (1) - report on current Samba connections
swat (8) - Samba Web Administration Tool
tdbbackup (8) - tool for backing up and ... of samba .tdb files
[root@RHEL4b samba]#
18.2. /usr/bin/testparm
18.2.1. syntax check smb.conf
To verify the syntax of the smb.conf file, you can use testparm.
[paul@RHEL4b ~]$ testparm
Load smb config files from /etc/samba/smb.conf
Processing section "[firstshare]"
Loaded services file OK.
Server role: ROLE_STANDALONE
Press enter to see a dump of your service definitions
18.2.2. testparm -v
An interesting option is testparm -v, which will output all the global options with their
default value.
[root@RHEL52 ~]# testparm -v | head
Load smb config files from /etc/samba/smb.conf
Processing section "[pub0]"
Processing section "[global$]"
Loaded services file OK.
Server role: ROLE_STANDALONE
Press enter to see a dump of your service definitions
[global]
dos charset = CP850
unix charset = UTF-8
display charset = LOCALE
workgroup = WORKGROUP
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realm =
netbios name = TEACHER0
netbios aliases =
netbios scope =
server string = Samba 3.0.28-1.el5_2.1
...
There were about 350 default values for smb.conf parameters in Samba 3.0.x. This number
grew to almost 400 in Samba 3.5.x.
18.2.3. testparm -s
The samba daemons are constantly (once every 60 seconds) checking the smb.conf file, so it
is good practice to keep this file small. But it is also good practice to document your samba
configuration, and to explicitly set options that have the same default values. The testparm
-s option allows you to do both. It will output the smallest possible samba configuration file,
while retaining all your settings. The idea is to have your samba configuration in another
file (like smb.conf.full) and let testparm parse this for you. The screenshot below shows you
how. First the smb.conf.full file with the explicitly set option workgroup to WORKGROUP.
[root@RHEL4b samba]# cat smb.conf.full
[global]
workgroup = WORKGROUP
# This is a demo of a documented smb.conf
# These two lines are removed by testparm -s
server string = Public Test Server
[firstshare]
path = /srv/samba/public
Next, we execute testparm with the -s option, and redirect stdout to the real smb.conf file.
[root@RHEL4b samba]# testparm -s smb.conf.full > smb.conf
Load smb config files from smb.conf.full
Processing section "[firstshare]"
Loaded services file OK.
And below is the end result. The two comment lines and the default option are no longer
there.
[root@RHEL4b samba]# cat smb.conf
# Global parameters
[global]
server string = Public Test Server
[firstshare]
path = /srv/samba/public
[root@RHEL4b samba]#
18.3. /usr/bin/smbclient
18.3.1. smbclient looking at Samba
With smbclient you can see browsing and share information from your smb server. It will
display all your shares, your workgroup, and the name of the Master Browser. The -N switch
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is added to avoid having to enter an empty password. The -L switch is followed by the name
of the host to check.
[root@RHEL4b init.d]# smbclient -NL rhel4b
Anonymous login successful
Domain=[WORKGROUP] OS=[Unix] Server=[Samba 3.0.10-1.4E.9]
Sharename Type Comment
--------- ---- -------
firstshare Disk
IPC$ IPC IPC Service (Public Test Server)
ADMIN$ IPC IPC Service (Public Test Server)
Anonymous login successful
Domain=[WORKGROUP] OS=[Unix] Server=[Samba 3.0.10-1.4E.9]
Server Comment
--------- -------
RHEL4B Public Test Server
WINXP
Workgroup Master
--------- -------
WORKGROUP WINXP
18.3.2. smbclient anonymous
The screenshot below uses smbclient to display information about a remote smb server (in
this case a computer with Ubuntu 11.10).
root@ubu1110:/etc/samba# testparm smbclient -NL 127.0.0.1
Anonymous login successful
Domain=[LINUXTR] OS=[Unix] Server=[Samba 3.5.11]
Sharename Type Comment
--------- ---- -------
share1 Disk
IPC$ IPC IPC Service (Samba 3.5.11)
Anonymous login successful
Domain=[LINUXTR] OS=[Unix] Server=[Samba 3.5.11]
Server Comment
--------- -------
Workgroup Master
--------- -------
LINUXTR DEBIAN6
WORKGROUP UBU1110
18.3.3. smbclient with credentials
Windows versions after xp sp2 and 2003 sp1 do not accept guest access (the
NT_STATUS_ACCESS_DENIED error). This example shows how to provide credentials
with smbclient.
[paul@RHEL53 ~]$ smbclient -L w2003 -U administrator%stargate
Domain=[W2003] OS=[Windows Server 2003 3790 Service Pack 2] Server=...
Sharename Type Comment
--------- ---- -------
C$ Disk Default share
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IPC$ IPC Remote IPC
ADMIN$ Disk Remote Admin
...
18.4. /usr/bin/smbtree
Another useful tool to troubleshoot Samba or simply to browse the SMB network is smbtree.
In its simplest form, smbtree will do an anonymous browsing on the local subnet. displaying
all SMB computers and (if authorized) their shares.
Let's take a look at two screenshots of smbtree in action (with blank password). The first
one is taken immediately after booting four different computers (one MS Windows 2000,
one MS Windows xp, one MS Windows 2003 and one RHEL 4 with Samba 3.0.10).
[paul@RHEL4b ~]$ smbtree
Password:
WORKGROUP
PEGASUS
\\WINXP
\\RHEL4B Pegasus Domain Member Server
Error connecting to 127.0.0.1 (Connection refused)
cli_full_connection: failed to connect to RHEL4B<20> (127.0.0.1)
\\HM2003
[paul@RHEL4b ~]$
The information displayed in the previous screenshot looks incomplete. The browsing
elections are still ongoing, the browse list is not yet distributed to all clients by the (to be
elected) browser master. The next screenshot was taken about one minute later. And it shows
even less.
[paul@RHEL4b ~]$ smbtree
Password:
WORKGROUP
\\W2000
[paul@RHEL4b ~]$
So we wait a while, and then run smbtree again, this time it looks a lot nicer.
[paul@RHEL4b ~]$ smbtree
Password:
WORKGROUP
\\W2000
PEGASUS
\\WINXP
\\RHEL4B Pegasus Domain Member Server
\\RHEL4B\ADMIN$ IPC Service (Pegasus Domain Member Server)
\\RHEL4B\IPC$ IPC Service (Pegasus Domain Member Server)
\\RHEL4B\domaindata Active Directory users only
\\HM2003
[paul@RHEL4b ~]$ smbtree --version
Version 3.0.10-1.4E.9
[paul@RHEL4b ~]$
I added the version number of smbtree in the previous screenshot, to show you the difference
when using the latest version of smbtree (below a screenshot taken from Ubuntu Feisty
Fawn). The latest version shows a more complete overview of machines and shares.
paul@laika:~$ smbtree --version
Version 3.0.24
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paul@laika:~$ smbtree
Password:
WORKGROUP
\\W2000
\\W2000\firstshare
\\W2000\C$ Default share
\\W2000\ADMIN$ Remote Admin
\\W2000\IPC$ Remote IPC
PEGASUS
\\WINXP
cli_rpc_pipe_open: cli_nt_create failed on pipe \srvsvc to machine WINXP.
Error was NT_STATUS_ACCESS_DENIED
\\RHEL4B Pegasus Domain Member Server
\\RHEL4B\ADMIN$ IPC Service (Pegasus Domain Member Server)
\\RHEL4B\IPC$ IPC Service (Pegasus Domain Member Server)
\\RHEL4B\domaindata Active Directory users only
\\HM2003
cli_rpc_pipe_open: cli_nt_create failed on pipe \srvsvc to machine HM2003.
Error was NT_STATUS_ACCESS_DENIED
paul@laika:~$
The previous screenshot also provides useful errors on why we cannot see shared info on
computers winxp and w2003. Let us try the old smbtree version on our RHEL server, but
this time with Administrator credentials (which are the same on all computers).
[paul@RHEL4b ~]$ smbtree -UAdministrator%Stargate1
WORKGROUP
\\W2000
PEGASUS
\\WINXP
\\WINXP\C$ Default share
\\WINXP\ADMIN$ Remote Admin
\\WINXP\share55
\\WINXP\IPC$ Remote IPC
\\RHEL4B Pegasus Domain Member Server
\\RHEL4B\ADMIN$ IPC Service (Pegasus Domain Member Server)
\\RHEL4B\IPC$ IPC Service (Pegasus Domain Member Server)
\\RHEL4B\domaindata Active Directory users only
\\HM2003
\\HM2003\NETLOGON Logon server share
\\HM2003\SYSVOL Logon server share
\\HM2003\WSUSTemp A network share used by Local Publishing ...
\\HM2003\ADMIN$ Remote Admin
\\HM2003\tools
\\HM2003\IPC$ Remote IPC
\\HM2003\WsusContent A network share to be used by Local ...
\\HM2003\C$ Default share
[paul@RHEL4b ~]$
As you can see, this gives a very nice overview of all SMB computers and their shares.
18.5. server string
The comment seen by the net view and the smbclient commands is the default value for
the server string option. Simply adding this value to the global section in smb.conf and
restarting samba will change the option.
[root@RHEL53 samba]# testparm -s 2>/dev/null | grep server
server string = Red Hat Server in Paris
After a short while, the changed option is visible on the Microsoft computers.
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C:\Documents and Settings\Administrator>net view
Server Name Remark
-------------------------------------------------------------------------------
\\LAIKA Ubuntu 9.04 server in Antwerp
\\RHEL53 Red Hat Server in Paris
\\W2003
18.6. Samba Web Administration Tool
(SWAT)
Samba comes with a web based tool to manage your samba configuration file. SWAT is
accessible with a web browser on port 901 of the host system. To enable the tool, first find
out whether your system is using the inetd or the xinetd superdaemon.
[root@RHEL4b samba]# ps fax | grep inet
15026 pts/0 S+ 0:00 \_ grep inet
2771 ? Ss 0:00 xinetd -stayalive -pidfile /var/run/xinetd.pid
[root@RHEL4b samba]#
Then edit the inetd.conf or change the disable = yes line in /etc/xinetd.d/swat to disable
= no.
[root@RHEL4b samba]# cat /etc/xinetd.d/swat
# default: off
# description: SWAT is the Samba Web Admin Tool. Use swat \
# to configure your Samba server. To use SWAT, \
# connect to port 901 with your favorite web browser.
service swat
{
port = 901
socket_type = stream
wait = no
only_from = 127.0.0.1
user = root
server = /usr/sbin/swat
log_on_failure += USERID
disable = no
}
[root@RHEL4b samba]# /etc/init.d/xinetd restart
Stopping xinetd: [ OK ]
Starting xinetd: [ OK ]
[root@RHEL4b samba]#
Change the only from value to enable swat from remote computers. This examples shows
how to provide swat access to all computers in a /24 subnet.
[root@RHEL53 xinetd.d]# grep only /etc/xinetd.d/swat
only_from = 192.168.1.0/24
Be careful when using SWAT, it erases all your manually edited comments in smb.conf.
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18.7. practice: getting started with samba
1. Take a backup copy of the original smb.conf, name it smb.conf.orig
2. Enable SWAT and take a look at it.
3. Stop the Samba server.
4. Create a minimalistic smb.conf.minimal and test it with testparm.
5. Use tesparm -s to create /etc/samba/smb.conf from your smb.conf.minimal .
6. Start Samba with your minimal smb.conf.
7. Verify with smbclient that your Samba server works.
8. Verify that another (Microsoft) computer can see your Samba server.
9. Browse the network with net view, smbtree and with Windows Explorer.
10. Change the "Server String" parameter in smb.conf. How long does it take before you see
the change (net view, smbclient, My Network Places,...) ?
11. Will restarting Samba after a change to smb.conf speed up the change ?
12. Which computer is the master browser master in your workgroup ? What is the master
browser ?
13. If time permits (or if you are waiting for other students to finish this practice), then install
a sniffer (wireshark) and watch the browser elections.
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18.8. solution: getting started with samba
1. Take a backup copy of the original smb.conf, name it smb.conf.orig
cd /etc/samba ; cp smb.conf smb.conf.orig
2. Enable SWAT and take a look at it.
on Debian/Ubuntu: vi /etc/inetd.conf (remove # before swat)
on RHEL/Fedora: vi /etc/xinetd.d/swat (set disable to no)
3. Stop the Samba server.
/etc/init.d/smb stop (Red Hat)
/etc/init.d/samba stop (Debian)
4. Create a minimalistic smb.conf.minimal and test it with testparm.
cd /etc/samba ; mkdir my_smb_confs ; cd my_smb_confs
vi smb.conf.minimal
testparm smb.conf.minimal
5. Use tesparm -s to create /etc/samba/smb.conf from your smb.conf.minimal .
testparm -s smb.conf.minimal > ../smb.conf
6. Start Samba with your minimal smb.conf.
/etc/init.d/smb restart (Red Hat)
/etc/init.d/samba restart (Debian)
7. Verify with smbclient that your Samba server works.
smbclient -NL 127.0.0.1
8. Verify that another computer can see your Samba server.
smbclient -NL 'ip-address' (on a Linux)
9. Browse the network with net view, smbtree and with Windows Explorer.
on Linux: smbtree
on Windows: net view (and WindowsKey + e)
10. Change the "Server String" parameter in smb.conf. How long does it take before you see
the change (net view, smbclient, My Network Places,...) ?
vi /etc/samba/smb.conf
(should take only seconds when restarting samba)
11. Will restarting Samba after a change to smb.conf speed up the change ?
yes
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12. Which computer is the master browser master in your workgroup ? What is the master
browser ?
The computer that won the elections.
This machine will make the list of computers in the network
13. If time permits (or if you are waiting for other students to finish this practice), then install
a sniffer (wireshark) and watch the browser elections.
On ubuntu: sudo aptitude install wireshark
then: sudo wireshark, select interface
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Chapter 19. a read only file server
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a read only file server
19.1. Setting up a directory to share
Let's start with setting up a very simple read only file server with Samba. Everyone (even
anonymous guests) will receive read access.
The first step is to create a directory and put some test files in it.
[root@RHEL52 ~]# mkdir -p /srv/samba/readonly
[root@RHEL52 ~]# cd /srv/samba/readonly/
[root@RHEL52 readonly]# echo "It is cold today." > winter.txt
[root@RHEL52 readonly]# echo "It is hot today." > summer.txt
[root@RHEL52 readonly]# ls -l
total 8
-rw-r--r-- 1 root root 17 Jan 21 05:49 summer.txt
-rw-r--r-- 1 root root 18 Jan 21 05:49 winter.txt
[root@RHEL52 readonly]#
19.2. configure the share
19.2.1. smb.conf [global] section
In this example the samba server is a member of WORKGROUP (the default workgroup).
We also set a descriptive server string, this string is visible to users browsing the network
with net view, windows explorer or smbclient.
[root@RHEL52 samba]# head -5 smb.conf
[global]
workgroup = WORKGROUP
server string = Public Anonymous File Server
netbios name = TEACHER0
security = share
You might have noticed the line with security = share. This line sets the default security
mode for our samba server. Setting the security mode to share will allow clients (smbclient,
any windows, another Samba server, ...) to provide a password for each share. This is one
way of using the SMB/CIFS protocol. The other way (called user mode) will allow the
client to provide a username/password combination, before the server knows which share
the client wants to access.
19.2.2. smb.conf [share] section
The share is called pubread and the path is set to our newly created directory. Everyone is
allowed access (guest ok = yes) and security is set to read only.
[pubread]
path = /srv/samba/readonly
comment = files to read
read only = yes
guest ok = yes
Here is a very similar configuration on Ubuntu 11.10.
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root@ubu1110:~# cat /etc/samba/smb.conf
[global]
workgroup = LINUXTR
netbios name = UBU1110
security = share
[roshare1]
path = /srv/samba/readonly
read only = yes
guest ok = yes
It doesn't really matter which Linux distribution you use. Below the same config on Debian
6, as good as identical.
root@debian6:~# cat /etc/samba/smb.conf
[global]
workgroup = LINUXTR
netbios name = DEBIAN6
security = share
[roshare1]
path = /srv/samba/readonly
read only = yes
guest ok = yes
19.3. restart the server
After testing with testparm, restart the samba server (so you don't have to wait).
[root@RHEL4b readonly]# service smb restart
Shutting down SMB services: [ OK ]
Shutting down NMB services: [ OK ]
Starting SMB services: [ OK ]
Starting NMB services: [ OK ]
19.4. verify the share
19.4.1. verify with smbclient
You can now verify the existence of the share with smbclient. Our pubread is listed as the
fourth share.
[root@RHEL52 samba]# smbclient -NL 127.0.0.1
Domain=[WORKGROUP] OS=[Unix] Server=[Samba 3.0.33-3.7.el5]
Sharename Type Comment
--------- ---- -------
IPC$ IPC IPC Service (Public Anonymous File Server)
global$ Disk
pub0 Disk
pubread Disk files to read
Domain=[WORKGROUP] OS=[Unix] Server=[Samba 3.0.33-3.7.el5]
Server Comment
--------- -------
TEACHER0 Samba 3.0.33-3.7.el5
W2003EE
Workgroup Master
--------- -------
WORKGROUP W2003EE
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19.4.2. verify on windows
The final test is to go to a Microsoft windows computer and read a file on the Samba server.
First we use the net use command to mount the pubread share on the driveletter k.
C:\>net use K: \\teacher0\pubread
The command completed successfully.
Then we test looking at the contents of the share, and reading the files.
C:\>dir k:
Volume in drive K is pubread
Volume Serial Number is 0C82-11F2
Directory of K:\
21/01/2009 05:49 <DIR> .
21/01/2009 05:49 <DIR> ..
21/01/2009 05:49 17 summer.txt
21/01/2009 05:49 18 winter.txt
2 File(s) 35 bytes
2 Dir(s) 13.496.242.176 bytes free
Just to be on the safe side, let us try writing.
K:\>echo very cold > winter.txt
Access is denied.
K:\>
Or you can use windows explorer...
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19.5. a note on netcat
The Windows command line screenshot is made in a Linux console, using netcat as a pipe
to a Windows command shell.
The way this works, is by enabling netcat to listen on the windows computer to a certain
port, executing cmd.exe when a connection is received. Netcat is similar to cat, in the way
that cat does nothing, only netcat does nothing over the network.
To enable this connection, type the following on the windows computer (after downloading
netcat for windows).
nc -l -p 23 -t -e cmd.exe
And then connect to this machine with netcat from any Linux computer. You end up with
a cmd.exe prompt inside your Linux shell.
paul@laika:~$ nc 192.168.1.38 23
Microsoft Windows [Version 5.2.3790]
(C) Copyright 1985-2003 Microsoft Corp.
C:\>net use k: /delete
net use k: /delete
k: was deleted successfully.
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19.6. practice: read only file server
1. Create a directory in a good location (FHS) to share files for everyone to read.
2. Make sure the directory is owned properly and is world accessible.
3. Put a textfile in this directory.
4. Share the directory with Samba.
5. Verify from your own and from another computer (smbclient, net use, ...) that the share
is accessible for reading.
6. Make a backup copy of your smb.conf, name it smb.conf.ReadOnlyFileServer.
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19.7. solution: read only file server
1. Create a directory in a good location (FHS) to share files for everyone to read.
choose one of these...
mkdir -p /srv/samba/readonly
mkdir -p /home/samba/readonly
/home/paul/readonly is wrong!!
/etc/samba/readonly is wrong!!
/readonly is wrong!!
2. Make sure the directory is owned properly and is world accessible.
chown root:root /srv/samba/readonly
chmod 755 /srv/samba/readonly
3. Put a textfile in this directory.
echo Hello World > hello.txt
4. Share the directory with Samba.
You smb.conf.readonly could look like this:
[global]
workgroup = WORKGROUP
server string = Read Only File Server
netbios name = STUDENTx
security = share
[readonlyX]
path = /srv/samba/readonly
comment = read only file share
read only = yes
guest ok = yes
test with testparm before going in production!
5. Verify from your own and from another computer (smbclient, net use, ...) that the share
is accessible for reading.
On Linux: smbclient -NL 127.0.0.1
On Windows Explorer: browse to My Network Places
On Windows cmd.exe: net use L: //studentx/readonly
6. Make a backup copy of your smb.conf, name it smb.conf.ReadOnlyFileServer.
cp smb.conf smb.conf.ReadOnlyFileServer
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Chapter 20. a writable file server
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20.1. set up a directory to share
In this second example, we will create a share where everyone can create files and write to
files. Again, we start by creating a directory
[root@RHEL52 samba]# mkdir -p /srv/samba/writable
[root@RHEL52 samba]# chmod 777 /srv/samba/writable/
20.2. share section in smb.conf
There are two parameters to make a share writable. We can use read only or writable. This
example shows how to use writable to give write access to a share.
writable = yes
And this is an example of using the read only parameter to give write access to a share.
read only = no
20.3. configure the share
Then we simply add a share to our file server by editing smb.conf. Below the check with
testparm. (We could have changed the description of the server...)
[root@RHEL52 samba]# testparm
Load smb config files from /etc/samba/smb.conf
Processing section "[pubwrite]"
Processing section "[pubread]"
Loaded services file OK.
Server role: ROLE_STANDALONE
Press enter to see a dump of your service definitions
[global]
netbios name = TEACHER0
server string = Public Anonymous File Server
security = SHARE
[pubwrite]
comment = files to write
path = /srv/samba/writable
read only = No
guest ok = Yes
[pubread]
comment = files to read
path = /srv/samba/readonly
guest ok = Yes
20.4. test connection with windows
We can now test the connection on a windows 2003 computer. We use the net use for this.
C:\>net use L: \\teacher0\pubwrite
net use L: \\teacher0\pubwrite
The command completed successfully.
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20.5. test writing with windows
We mounted the pubwrite share on the L: drive in windows. Below we test that we can
write to this share.
L:\>echo hoi > hoi.txt
L:\>dir
Volume in drive L is pubwrite
Volume Serial Number is 0C82-272A
Directory of L:\
21/01/2009 06:11 <DIR> .
21/01/2009 06:11 <DIR> ..
21/01/2009 06:16 6 hoi.txt
1 File(s) 6 bytes
2 Dir(s) 13.496.238.080 bytes free
20.6. How is this possible ?
Linux (or any Unix) always needs a user account to gain access to a system. The windows
computer did not provide the samba server with a user account or a password. Instead,
the Linux owner of the files created through this writable share is the Linux guest account
(usually named nobody).
[root@RHEL52 samba]# ls -l /srv/samba/writable/
total 4
-rwxr--r-- 1 nobody nobody 6 Jan 21 06:16 hoi.txt
So this is not the cleanest solution. We will need to improve this.
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20.7. practice: writable file server
1. Create a directory and share it with Samba.
2. Make sure everyone can read and write files, test writing with smbclient and from a
Microsoft computer.
3. Verify the ownership of files created by (various) users.
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20.8. solution: writable file server
1. Create a directory and share it with Samba.
mkdir /srv/samba/writable
chmod 777 /srv/samba/writable
the share section in smb.conf can look like this:
[pubwrite]
path = /srv/samba/writable
comment = files to write
read only = no
guest ok = yes
2. Make sure everyone can read and write files, test writing with smbclient and from a
Microsoft computer.
to test writing with smbclient:
echo one > count.txt
echo two >> count.txt
echo three >> count.txt
smbclient //localhost/pubwrite
Password:
smb: \> put count.txt
3. Verify the ownership of files created by (various) users.
ls -l /srv/samba/writable
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Chapter 21. samba first user account
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samba first user account
21.1. creating a samba user
We will create a user for our samba file server and make this user the owner of the directory
and all of its files. This anonymous user gets a clear description, but does not get a login shell.
[root@RHEL52 samba]# useradd -s /bin/false sambanobody
[root@RHEL52 samba]# usermod -c "Anonymous Samba Access" sambanobody
[root@RHEL52 samba]# passwd sambanobody
Changing password for user sambanobody.
New UNIX password:
Retype new UNIX password:
passwd: all authentication tokens updated successfully.
21.2. ownership of files
We can use this user as owner of files and directories, instead of using the root account. This
approach is clear and more secure.
[root@RHEL52 samba]# chown -R sambanobody:sambanobody /srv/samba/
[root@RHEL52 samba]# ls -al /srv/samba/writable/
total 12
drwxrwxrwx 2 sambanobody sambanobody 4096 Jan 21 06:11 .
drwxr-xr-x 6 sambanobody sambanobody 4096 Jan 21 06:11 ..
-rwxr--r-- 1 sambanobody sambanobody 6 Jan 21 06:16 hoi.txt
21.3. /usr/bin/smbpasswd
The sambanobody user account that we created in the previous examples is not yet used
by samba. It just owns the files and directories that we created for our shares. The goal of
this section is to force ownership of files created through the samba share to belong to our
sambanobody user. Remember, our server is still accessible to everyone, nobody needs to
know this user account or password. We just want a clean Linux server.
To accomplish this, we first have to tell Samba about this user. We can do this by adding
the account to smbpasswd.
[root@RHEL52 samba]# smbpasswd -a sambanobody
New SMB password:
Retype new SMB password:
Added user sambanobody.
21.4. /etc/samba/smbpasswd
To find out where Samba keeps this information (for now), use smbd -b. The
PRIVATE_DIR variable will show you where the smbpasswd database is located.
[root@RHEL52 samba]# smbd -b | grep PRIVATE
PRIVATE_DIR: /etc/samba
[root@RHEL52 samba]# ls -l smbpasswd
-rw------- 1 root root 110 Jan 21 06:19 smbpasswd
You can use a simple cat to see the contents of the smbpasswd database. The sambanobody
user does have a password (it is secret).
[root@RHEL52 samba]# cat smbpasswd
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sambanobody:503:AE9 ... 9DB309C528E540978:[U ]:LCT-4976B05B:
21.5. passdb backend
Note that recent versions of Samba have tdbsam as default for the passdb backend
paramater.
root@ubu1110:~# testparm -v 2>/dev/null| grep 'passdb backend'
passdb backend = tdbsam
21.6. forcing this user
Now that Samba knows about this user, we can adjust our writable share to force the
ownership of files created through it. For this we use the force user and force group options.
Now we can be sure that all files in the Samba writable share are owned by the same
sambanobody user.
Below is the renewed definition of our share in smb.conf.
[pubwrite]
path = /srv/samba/writable
comment = files to write
force user = sambanobody
force group = sambanobody
read only = no
guest ok = yes
When you reconnect to the share and write a file, then this sambanobody user will own the
newly created file (and nobody needs to know the password).
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21.7. practice: first samba user account
1. Create a user account for use with samba.
2. Add this user to samba's user database.
3. Create a writable shared directory and use the "force user" and "force group" directives
to force ownership of files.
4. Test the working of force user with smbclient, net use and Windows Explorer.
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21.8. solution: first samba user account
1. Create a user account for use with samba.
useradd -s /bin/false smbguest
usermod -c 'samba guest'
passwd smbguest
2. Add this user to samba's user database.
smbpasswd -a smbguest
3. Create a writable shared directory and use the "force user" and "force group" directives
to force ownership of files.
[userwrite]
path = /srv/samba/userwrite
comment = everyone writes files owned by smbguest
read only = no
guest ok = yes
force user = smbguest
force group = smbguest
4. Test the working of force user with smbclient, net use and Windows Explorer.
ls -l /srv/samba/userwrite (and verify ownership)
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Chapter 22. samba authentication
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samba authentication
22.1. creating the users on Linux
The goal of this example is to set up a file share accessible to a number of different users.
The users will need to authenticate with their password before access to this share is granted.
We will first create three randomly named users, each with their own password. First we
add these users to Linux.
[root@RHEL52 ~]# useradd -c "Serena Williams" serena
[root@RHEL52 ~]# useradd -c "Justine Henin" justine
[root@RHEL52 ~]# useradd -c "Martina Hingis" martina
[root@RHEL52 ~]# passwd serena
Changing password for user serena.
New UNIX password:
Retype new UNIX password:
passwd: all authentication tokens updated successfully.
[root@RHEL52 ~]# passwd justine
Changing password for user justine.
New UNIX password:
Retype new UNIX password:
passwd: all authentication tokens updated successfully.
[root@RHEL52 ~]# passwd martina
Changing password for user martina.
New UNIX password:
Retype new UNIX password:
passwd: all authentication tokens updated successfully.
22.2. creating the users on samba
Then we add them to the smbpasswd file, with the same password.
[root@RHEL52 ~]# smbpasswd -a serena
New SMB password:
Retype new SMB password:
Added user serena.
[root@RHEL52 ~]# smbpasswd -a justine
New SMB password:
Retype new SMB password:
Added user justine.
[root@RHEL52 ~]# smbpasswd -a martina
New SMB password:
Retype new SMB password:
Added user martina.
22.3. security = user
Remember that we set samba's security mode to share with the security = share directive in
the [global] section ? Since we now require users to always provide a userid and password
for access to our samba server, we will need to change this. Setting security = user will
require the client to provide samba with a valid userid and password before giving access
to a share.
Our [global] section now looks like this.
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[global]
workgroup = WORKGROUP
netbios name = TEACHER0
server string = Samba File Server
security = user
22.4. configuring the share
We add the following [share] section to our smb.conf (and we do not forget to create the
directory /srv/samba/authwrite).
[authwrite]
path = /srv/samba/authwrite
comment = authenticated users only
read only = no
guest ok = no
22.5. testing access with net use
After restarting samba, we test with different users from within Microsoft computers. The
screenshots use the net useFirst serena from Windows XP.
C:\>net use m: \\teacher0\authwrite stargate /user:serena
The command completed successfully.
C:\>m:
M:\>echo greetings from Serena > serena.txt
The next screenshot is martina on a Windows 2000 computer, she succeeds in writing her
files, but fails to overwrite the file from serena.
C:\>net use k: \\teacher0\authwrite stargate /user:martina
The command completed successfully.
C:\>k:
K:\>echo greetings from martina > Martina.txt
K:\>echo test overwrite > serena.txt
Access is denied.
22.6. testing access with smbclient
You can also test connecting with authentication with smbclient. First we test with a wrong
password.
[root@RHEL52 samba]# smbclient //teacher0/authwrite -U martina wrongpass
session setup failed: NT_STATUS_LOGON_FAILURE
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Then we test with the correct password, and verify that we can access a file on the share.
[root@RHEL52 samba]# smbclient //teacher0/authwrite -U martina stargate
Domain=[TEACHER0] OS=[Unix] Server=[Samba 3.0.33-3.7.el5]
smb: \> more serena.txt
getting file \serena.txt of size 14 as /tmp/smbmore.QQfmSN (6.8 kb/s)
one
two
three
smb: \> q
22.7. verify ownership
We now have a simple standalone samba file server with authenticated access. And the files
in the shares belong to their proper owners.
[root@RHEL52 samba]# ls -l /srv/samba/authwrite/
total 8
-rwxr--r-- 1 martina martina 0 Jan 21 20:06 martina.txt
-rwxr--r-- 1 serena serena 14 Jan 21 20:06 serena.txt
-rwxr--r-- 1 serena serena 6 Jan 21 20:09 ser.txt
22.8. common problems
22.8.1. NT_STATUS_BAD_NETWORK_NAME
You can get NT_STATUS_BAD_NETWORK_NAME when you forget to create the
target directory.
[root@RHEL52 samba]# rm -rf /srv/samba/authwrite/
[root@RHEL52 samba]# smbclient //teacher0/authwrite -U martina stargate
Domain=[TEACHER0] OS=[Unix] Server=[Samba 3.0.33-3.7.el5]
tree connect failed: NT_STATUS_BAD_NETWORK_NAME
22.8.2. NT_STATUS_LOGON_FAILURE
You can get NT_STATUS_LOGON_FAILURE when you type the wrong password or
when you type an unexisting username.
[root@RHEL52 samba]# smbclient //teacher0/authwrite -U martina STARGATE
session setup failed: NT_STATUS_LOGON_FAILURE
22.8.3. usernames are (not) case sensitive
Remember that usernames om Linux are case sensitive.
[root@RHEL52 samba]# su - MARTINA
su: user MARTINA does not exist
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[root@RHEL52 samba]# su - martina
[martina@RHEL52 ~]$
But usernames on Microsoft computers are not case sensitive.
[root@RHEL52 samba]# smbclient //teacher0/authwrite -U martina stargate
Domain=[TEACHER0] OS=[Unix] Server=[Samba 3.0.33-3.7.el5]
smb: \> q
[root@RHEL52 samba]# smbclient //teacher0/authwrite -U MARTINA stargate
Domain=[TEACHER0] OS=[Unix] Server=[Samba 3.0.33-3.7.el5]
smb: \> q
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22.9. practice : samba authentication
0. Make sure you have properly named backups of your smb.conf of the previous practices.
1. Create three users (on the Linux and on the samba), remember their passwords!
2. Set up a shared directory that is only accessible to authenticated users.
3. Use smbclient and a windows computer to access your share, use more than one user
account (windows requires a logoff/logon for this).
4. Verify that files created by these users belong to them.
5. Try to change or delete a file from another user.
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22.10. solution: samba authentication
1. Create three users (on the Linux and on the samba), remember their passwords!
useradd -c 'SMB user1' userx
passwd userx
2. Set up a shared directory that is only accessible to authenticated users.
The shared section in smb.conf could look like this:
[authwrite]
path = /srv/samba/authwrite
comment = authenticated users only
read only = no
guest ok = no
3. Use smbclient and a windows computer to access your share, use more than one user
account (windows requires a logoff/logon for this).
on Linux: smbclient //studentX/authwrite -U user1 password
on windows net use p: \\studentX\authwrite password /user:user2
4. Verify that files created by these users belong to them.
ls -l /srv/samba/authwrite
5. Try to change or delete a file from another user.
you should not be able to change or overwrite files from others.
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Chapter 23. samba securing shares
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samba securing shares
23.1. security based on user name
23.1.1. valid users
To restrict users per share, you can use the valid users parameter. In the example below,
only the users listed as valid will be able to access the tennis share.
[tennis]
path = /srv/samba/tennis
comment = authenticated and valid users only
read only = No
guest ok = No
valid users = serena, kim, venus, justine
23.1.2. invalid users
If you are paranoia, you can also use invalid users to explicitely deny the listed users access.
When a user is in both lists, the user has no access!
[tennis]
path = /srv/samba/tennis
read only = No
guest ok = No
valid users = kim, serena, venus, justine
invalid users = venus
23.1.3. read list
On a writable share, you can set a list of read only users with the read list parameter.
[football]
path = /srv/samba/football
read only = No
guest ok = No
read list = martina, roberto
23.1.4. write list
Even on a read only share, you can set a list of users that can write. Use the write list
parameter.
[football]
path = /srv/samba/golf
read only = Yes
guest ok = No
write list = eddy, jan
23.2. security based on ip-address
23.2.1. hosts allow
The hosts allow or allow hosts parameter is one of the key advantages of Samba. It allows
access control of shares on the ip-address level. To allow only specific hosts to access a
share, list the hosts, separated by comma's.
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allow hosts = 192.168.1.5, 192.168.1.40
Allowing entire subnets is done by ending the range with a dot.
allow hosts = 192.168.1.
Subnet masks can be added in the classical way.
allow hosts = 10.0.0.0/255.0.0.0
You can also allow an entire subnet with exceptions.
hosts allow = 10. except 10.0.0.12
23.2.2. hosts deny
The hosts deny or deny hosts parameter is the logical counterpart of the previous. The
syntax is the same as for hosts allow.
hosts deny = 192.168.1.55, 192.168.1.56
23.3. security through obscurity
23.3.1. hide unreadable
Setting hide unreadable to yes will prevent users from seeing files that cannot be read by
them.
hide unreadable = yes
23.3.2. browsable
Setting the browseable = no directive will hide shares from My Network Places. But it will
not prevent someone from accessing the share (when the name of the share is known).
Note that browsable and browseable are both correct syntax.
[pubread]
path = /srv/samba/readonly
comment = files to read
read only = yes
guest ok = yes
browseable = no
23.4. file system security
23.4.1. create mask
You can use create mask and directory mask to set the maximum allowed permissions for
newly created files and directories. The mask you set is an AND mask (it takes permissions
away).
[tennis]
path = /srv/samba/tennis
read only = No
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guest ok = No
create mask = 640
directory mask = 750
23.4.2. force create mode
Similar to create mask, but different. Where the mask from above was a logical AND, the
mode you set here is a logical OR (so it adds permissions). You can use the force create
mode and force directory mode to set the minimal required permissions for newly created
files and directories.
[tennis]
path = /srv/samba/tennis
read only = No
guest ok = No
force create mode = 444
force directory mode = 550
23.4.3. security mask
The security mask and directory security mask work in the same way as create mask
and directory mask, but apply only when a windows user is changing permissions using
the windows security dialog box.
23.4.4. force security mode
The force security mode and force directory security mode work in the same way as force
create mode and force directory mode, but apply only when a windows user is changing
permissions using the windows security dialog box.
23.4.5. inherit permissions
With inherit permissions = yes you can force newly created files and directories to inherit
permissions from their parent directory, overriding the create mask and directory mask
settings.
[authwrite]
path = /srv/samba/authwrite
comment = authenticated users only
read only = no
guest ok = no
create mask = 600
directory mask = 555
inherit permissions = yes
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23.5. practice: securing shares
1. Create a writable share called sales, and a readonly share called budget. Test that it works.
2. Limit access to the sales share to ann, sandra and veronique.
3. Make sure that roberto cannot access the sales share.
4. Even though the sales share is writable, ann should only have read access.
5. Even though the budget share is read only, sandra should also have write access.
6. Limit one shared directory to the 192.168.1.0/24 subnet, and another share to the two
computers with ip-addresses 192.168.1.33 and 172.17.18.19.
7. Make sure the computer with ip 192.168.1.203 cannot access the budget share.
8. Make sure (on the budget share) that users can see only files and directories to which
they have access.
9. Make sure the sales share is not visible when browsing the network.
10. All files created in the sales share should have 640 permissions or less.
11. All directories created in the budget share should have 750 permissions or more.
12. Permissions for files on the sales share should never be set more than 664.
13. Permissions for files on the budget share should never be set less than 500.
14. If time permits (or if you are waiting for other students to finish this practice), then
combine the "read only" and "writable" statements to check which one has priority.
15. If time permits then combine "read list", "write list", "hosts allow" and "hosts deny".
Which of these has priority ?
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23.6. solution: securing shares
1. Create a writable share called sales, and a readonly share called budget. Test that it works.
see previous solutions on how to do this...
2. Limit access to the sales share to ann, sandra and veronique.
valid users = ann, sandra, veronique
3. Make sure that roberto cannot access the sales share.
invalid users = roberto
4. Even though the sales share is writable, ann should only have read access.
read list = ann
5. Even though the budget share is read only, sandra should also have write access.
write list = sandra
6. Limit one shared directory to the 192.168.1.0/24 subnet, and another share to the two
computers with ip-addresses 192.168.1.33 and 172.17.18.19.
hosts allow = 192.168.1.
hosts allow = 192.168.1.33, 172.17.18.19
7. Make sure the computer with ip 192.168.1.203 cannot access the budget share.
hosts deny = 192.168.1.203
8. Make sure (on the budget share) that users can see only files and directories to which
they have access.
hide unreadable = yes
9. Make sure the sales share is not visible when browsing the network.
browsable = no
10. All files created in the sales share should have 640 permissions or less.
create mask = 640
11. All directories created in the budget share should have 750 permissions or more.
force directory mode = 750
12. Permissions for files on the sales share should never be set more than 664.
security mask = 750
13. Permissions for files on the budget share should never be set less than 500.
force security directory mask = 500
14. If time permits (or if you are waiting for other students to finish this practice), then
combine the "read only" and "writable" statements to check which one has priority.
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15. If time permits then combine "read list", "write list", "hosts allow" and "hosts deny".
Which of these has priority ?
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Chapter 24. samba domain member
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24.1. changes in smb.conf
24.1.1. workgroup
The workgroup option in the global section should match the netbios name of the Active
Directory domain.
workgroup = STARGATE
24.1.2. security mode
Authentication will not be handled by samba now, but by the Active Directory domain
controllers, so we set the security option to domain.
security = Domain
24.1.3. Linux uid's
Linux requires a user account for every user accessing its file system, we need to provide
Samba with a range of uid's and gid's that it can use to create these user accounts. The range
is determined with the idmap uid and the idmap gid parameters. The first Active Directory
user to connect will receive Linux uid 20000.
idmap uid = 20000-22000
idmap gid = 20000-22000
24.1.4. winbind use default domain
The winbind use default domain parameter makes sure winbind also operates on users
without a domain component in their name.
winbind use default domain = yes
24.1.5. [global] section in smb.conf
Below is our new global section in smb.conf.
[global]
workgroup = STARGATE
security = Domain
server string = Stargate Domain Member Server
idmap uid = 20000-22000
idmap gid = 20000-22000
winbind use default domain = yes
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24.1.6. realm in /etc/krb5.conf
To connect to a Windows 2003 sp2 (or later) you will need to adjust the kerberos realm in
/etc/krb5.conf and set both lookup statements to true.
[libdefaults]
default_realm = STARGATE.LOCAL
dns_lookup_realm = true
dns_lookup_kdc = true
24.1.7. [share] section in smb.conf
Nothing special is required for the share section in smb.conf. Remember that we do not
manually create users in smbpasswd or on the Linux (/etc/passwd). Only Active Directory
users are allowed access.
[domaindata]
path = /srv/samba/domaindata
comment = Active Directory users only
read only = No
24.2. joining an Active Directory domain
While the Samba server is stopped, you can use net rpc join to join the Active Directory
domain.
[root@RHEL52 samba]# service smb stop
Shutting down SMB services: [ OK ]
Shutting down NMB services: [ OK ]
[root@RHEL52 samba]# net rpc join -U Administrator
Password:
Joined domain STARGATE.
We can verify in the aduc (Active Directory Users and Computers) that a computer account
is created for this samba server.
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24.3. winbind
24.3.1. adding winbind to nsswitch.conf
The winbind daemon is talking with the Active Directory domain.
We need to update the /etc/nsswitch.conf file now, so user group and host names can be
resolved against the winbind daemon.
[root@RHEL52 samba]# vi /etc/nsswitch.conf
[root@RHEL52 samba]# grep winbind /etc/nsswitch.conf
passwd: files winbind
group: files winbind
hosts: files dns winbind
24.3.2. starting samba and winbindd
Time to start Samba followed by winbindd.
[root@RHEL4b samba]# service smb start
Starting SMB services: [ OK ]
Starting NMB services: [ OK ]
[root@RHEL4b samba]# service winbind start
Starting winbindd services: [ OK ]
[root@RHEL4b samba]#
24.4. wbinfo
24.4.1. verify the trust
You can use wbinfo -t to verify the trust between your samba server and Active Directory.
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[root@RHEL52 ~]# wbinfo -t
checking the trust secret via RPC calls succeeded
24.4.2. list all users
We can obtain a list of all user with the wbinfo -u command. The domain is not shown when
the winbind use default domain parameter is set.
[root@RHEL52 ~]# wbinfo -u
TEACHER0\serena
TEACHER0\justine
TEACHER0\martina
STARGATE\administrator
STARGATE\guest
STARGATE\support_388945a0
STARGATE\pol
STARGATE\krbtgt
STARGATE\arthur
STARGATE\harry
24.4.3. list all groups
We can obtain a list of all domain groups with the wbinfo -g command. The domain is not
shown when the winbind use default domain parameter is set.
[root@RHEL52 ~]# wbinfo -g
BUILTIN\administrators
BUILTIN\users
BATMAN\domain computers
BATMAN\domain controllers
BATMAN\schema admins
BATMAN\enterprise admins
BATMAN\domain admins
BATMAN\domain users
BATMAN\domain guests
BATMAN\group policy creator owners
BATMAN\dnsupdateproxy
24.4.4. query a user
We can use wbinfo -a to verify authentication of a user against Active Directory. Assuming
a user account harry with password stargate is just created on the Active Directory, we get
the following screenshot.
[root@RHEL52 ~]# wbinfo -a harry%stargate
plaintext password authentication succeeded
challenge/response password authentication succeeded
24.5. getent
We can use getent to verify that winbindd is working and actually adding the Active
directory users to /etc/passwd.
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[root@RHEL52 ~]# getent passwd harry
harry:*:20000:20008:harry potter:/home/BATMAN/harry:/bin/false
[root@RHEL52 ~]# getent passwd arthur
arthur:*:20001:20008:arthur dent:/home/BATMAN/arthur:/bin/false
[root@RHEL52 ~]# getent passwd bilbo
bilbo:*:20002:20008:bilbo baggins:/home/BATMAN/bilbo:/bin/false
If the user already exists locally, then the local user account is shown. This is because
winbind is configured in /etc/nsswitch.conf after files.
[root@RHEL52 ~]# getent passwd paul
paul:x:500:500:Paul Cobbaut:/home/paul:/bin/bash
All the Active Directory users can now easily connect to the Samba share. Files created by
them, belong to them.
24.6. file ownership
[root@RHEL4b samba]# ll /srv/samba/domaindata/
total 0
-rwxr--r-- 1 justine 20000 0 Jun 22 19:54 create_by_justine_on_winxp.txt
-rwxr--r-- 1 venus 20000 0 Jun 22 19:55 create_by_venus.txt
-rwxr--r-- 1 maria 20000 0 Jun 22 19:57 Maria.txt
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samba domain member
24.7. practice : samba domain member
1. Verify that you have a working Active Directory (AD) domain.
2. Add the domain name and domain controller to /etc/hosts. Set the AD-DNS in /etc/
resolv.conf.
3. Setup Samba as a member server in the domain.
4. Verify the creation of a computer account in AD for your Samba server.
5. Verify the automatic creation of AD users in /etc/passwd with wbinfo and getent.
6. Connect to Samba shares with AD users, and verify ownership of their files.
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Chapter 25. samba domain controller
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samba domain controller
25.1. about Domain Controllers
25.1.1. Windows NT4
Windows NT4 works with single master replication domain controllers. There is exactly one
PDC (Primary Domain Controller) in the domain, and zero or more BDC's (Backup Domain
Controllers). Samba 3 has all features found in Windows NT4 PDC and BDC, and more.
This includes file and print serving, domain control with single logon, logon scripts, home
directories and roaming profiles.
25.1.2. Windows 200x
With Windows 2000 came Active Directory. AD includes multimaster replication and group
policies. Samba 3 can only be a member server in Active Directory, it cannot manage group
policies. Samba 4 can do this (in beta).
25.1.3. Samba 3
Samba 3 can act as a domain controller in its own domain. In a Windows NT4 domain, with
one Windows NT4 PDC and zero or more BDC's, Samba 3 can only be a member server.
The same is valid for Samba 3 in an Active Directory Domain. In short, a Samba 3 domain
controller can not share domain control with Windows domain controllers.
25.1.4. Samba 4
Samba 4 can be a domain controller in an Active Directory domain, including managing
group policies. As of this writing, Samba 4 is not released for production!
25.2. About security modes
25.2.1. security = share
The 'Windows for Workgroups' way of working, a client requests connection to a share
and provides a password for that connection. Aanyone who knows a password for a share
can access that share. This security model was common in Windows 3.11, Windows 95,
Windows 98 and Windows ME.
25.2.2. security = user
The client will send a userid + password before the server knows which share the client
wants to access. This mode should be used whenever the samba server is in control of the
user database. Both for standalone and samba domain controllers.
25.2.3. security = domain
This mode will allow samba to verify user credentials using NTLM in Windows NT4 and
in all Active Directory domains. This is similar to Windows NT4 BDC's joining a native
Windows 2000/3 Active Directory domain.
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samba domain controller
25.2.4. security = ads
This mode will make samba use Kerberos to connect to the Active Directory domain.
25.2.5. security = server
This mode is obsolete, it can be used to forward authentication to another server.
25.3. About password backends
The previous chapters all used the smbpasswd user database. For domain control we opt
for the tdbsam password backend. Another option would be to use LDAP. Larger domains
will benefit from using LDAP instead of the not so scalable tdbsam. When you need more
than one Domain Controller, then the Samba team advises to not use tdbsam.
25.4. [global] section in smb.conf
Now is a good time to start adding comments in your smb.conf. First we will take a look at
the naming of our domain and server in the [global] section, and at the domain controlling
parameters.
25.4.1. security
The security must be set to user (which is the default). This mode will make samba control
the user accounts, so it will allow samba to act as a domain controller.
security = user
25.4.2. os level
A samba server is the most stable computer in the network, so it should win all browser
elections (os level above 32) to become the browser master
os level = 33
25.4.3. passdb backend
The passdb backend parameter will determine whether samba uses smbpasswd, tdbsam
or ldap.
passdb backend = tdbsam
25.4.4. preferred master
Setting the preferred master parameter to yes will make the nmbd daemon force an election
on startup.
preferred master = yes
25.4.5. domain logons
Setting the domain logons parameter will make this samba server a domain controller.
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samba domain controller
domain logons = yes
25.4.6. domain master
Setting the domain master parameter can cause samba to claim the domain master
browser role for its workgroup. Don't use this parameter in a workgroup with an active
NT4 PDC.
domain master = yes
25.4.7. [global] section
The screenshot below shows a sample [global] section for a samba domain controller.
[global]
# names
workgroup = SPORTS
netbios name = DCSPORTS
server string = Sports Domain Controller
# domain control parameters
security = user
os level = 33
preferred master = Yes
domain master = Yes
domain logons = Yes
25.5. netlogon share
Part of the microsoft definition for a domain controller is that it should have a netlogon
share. This is the relevant part of smb.conf to create this netlogon share on Samba.
[netlogon]
comment = Network Logon Service
path = /srv/samba/netlogon
admin users = root
guest ok = Yes
browseable = No
25.6. other [share] sections
We create some sections for file shares, to test the samba server. Users can all access the
general sports file share, but only group members can access their own sports share.
[sports]
comment = Information about all sports
path = /srv/samba/sports
valid users = @ntsports
read only = No
[tennis]
comment = Information about tennis
path = /srv/samba/tennis
valid users = @nttennis
read only = No
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samba domain controller
[football]
comment = Information about football
path = /srv/samba/football
valid users = @ntfootball
read only = No
25.7. Users and Groups
To be able to use users and groups in the samba domain controller, we can first set up some
groups on the Linux computer.
[root@RHEL52 samba]# groupadd ntadmins
[root@RHEL52 samba]# groupadd ntsports
[root@RHEL52 samba]# groupadd ntfootball
[root@RHEL52 samba]# groupadd nttennis
This enables us to add group membership info to some new users for our samba domain.
Don't forget to give them a password.
[root@RHEL52 samba]# useradd -m -G ntadmins Administrator
[root@RHEL52 samba]# useradd -m -G ntsports,nttennis venus
[root@RHEL52 samba]# useradd -m -G ntsports,nttennis kim
[root@RHEL52 samba]# useradd -m -G ntsports,nttennis jelena
[root@RHEL52 samba]# useradd -m -G ntsports,ntfootball figo
[root@RHEL52 samba]# useradd -m -G ntsports,ntfootball ronaldo
[root@RHEL52 samba]# useradd -m -G ntsports,ntfootball pfaff
It is always safe to verify creation of users, groups and passwords in /etc/passwd, /etc/shadow
and /etc/group.
[root@RHEL52 samba]# tail -11 /etc/group
ntadmins:x:507:Administrator
ntsports:x:508:venus,kim,jelena,figo,ronaldo,pfaff
ntfootball:x:509:figo,ronaldo,pfaff
nttennis:x:510:venus,kim,jelena
Administrator:x:511:
venus:x:512:
kim:x:513:
jelena:x:514:
figo:x:515:
ronaldo:x:516:
pfaff:x:517:
25.8. tdbsam
Next we must make these users known to samba with the smbpasswd tool. When you add
the first user to tdbsam, the file /etc/samba/passdb.tdb will be created.
[root@RHEL52 samba]# smbpasswd -a root
New SMB password:
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samba domain controller
Retype new SMB password:
tdbsam_open: Converting version 0 database to version 3.
Added user root.
Adding all the other users generates less output, because tdbsam is already created.
[root@RHEL4b samba]# smbpasswd -a root
New SMB password:
Retype new SMB password:
Added user root.
25.9. about computer accounts
Every NT computer (Windows NT, 2000, XP, Vista) can become a member of a domain.
Joining the domain (by right-clicking on My Computer) means that a computer account will
be created in the domain. This computer account also has a password (but you cannot know
it) to prevent other computers with the same name from accidentally becoming member of
the domain. The computer account created by Samba is visible in the /etc/passwd file on
Linux. Computer accounts appear as a normal user account, but end their name with a dollar
sign. Below a screenshot of the windows 2003 computer account, created by Samba 3.
[root@RHEL52 samba]# tail -5 /etc/passwd
jelena:x:510:514::/home/jelena:/bin/bash
figo:x:511:515::/home/figo:/bin/bash
ronaldo:x:512:516::/home/ronaldo:/bin/bash
pfaff:x:513:517::/home/pfaff:/bin/bash
w2003ee$:x:514:518::/home/nobody:/bin/false
To be able to create the account, you will need to provide credentials of an account with
the permission to create accounts (by default only root can do this on Linux). And we will
have to tell Samba how to to this, by adding an add machine script to the global section
of smb.conf.
add machine script = /usr/sbin/useradd -s /bin/false -d /home/nobody %u
You can now join a Microsoft computer to the sports domain (with the root user). After
reboot of the Microsoft computer, you will be able to logon with Administrator (password
Stargate1), but you will get an error about your roaming profile. We will fix this in the next
section.
When joining the samba domain, you have to enter the credentials of a Linux account that
can create users (usually only root can do this). If the Microsoft computer complains with
The parameter is incorrect, then you possibly forgot to add the add machine script.
25.10. local or roaming profiles
For your information, if you want to force local profiles instead of roaming profiles, then
simply add the following two lines to the global section in smb.conf.
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samba domain controller
logon home =
logon path =
Microsoft computers store a lot of User Metadata and application data in a user profile.
Making this profile available on the network will enable users to keep their Desktop and
Application settings across computers. User profiles on the network are called roaming
profiles or roving profiles. The Samba domain controller can manage these profiles. First
we need to add the relevant section in smb.conf.
[Profiles]
comment = User Profiles
path = /srv/samba/profiles
readonly = No
profile acls = Yes
Besides the share section, we also need to set the location of the profiles share (this can be
another Samba server) in the global section.
logon path = \\%L\Profiles\%U
The %L variable is the name of this Samba server, the %U variable translates to the
username. After adding a user to smbpasswd and letting the user log on and off, the profile
of the user will look like this.
[root@RHEL4b samba]# ll /srv/samba/profiles/Venus/
total 568
drwxr-xr-x 4 Venus Venus 4096 Jul 5 10:03 Application Data
drwxr-xr-x 2 Venus Venus 4096 Jul 5 10:03 Cookies
drwxr-xr-x 3 Venus Venus 4096 Jul 5 10:03 Desktop
drwxr-xr-x 3 Venus Venus 4096 Jul 5 10:03 Favorites
drwxr-xr-x 4 Venus Venus 4096 Jul 5 10:03 My Documents
drwxr-xr-x 2 Venus Venus 4096 Jul 5 10:03 NetHood
-rwxr--r-- 1 Venus Venus 524288 Jul 5 2007 NTUSER.DAT
-rwxr--r-- 1 Venus Venus 1024 Jul 5 2007 NTUSER.DAT.LOG
-rw-r--r-- 1 Venus Venus 268 Jul 5 10:03 ntuser.ini
drwxr-xr-x 2 Venus Venus 4096 Jul 5 10:03 PrintHood
drwxr-xr-x 2 Venus Venus 4096 Jul 5 10:03 Recent
drwxr-xr-x 2 Venus Venus 4096 Jul 5 10:03 SendTo
drwxr-xr-x 3 Venus Venus 4096 Jul 5 10:03 Start Menu
drwxr-xr-x 2 Venus Venus 4096 Jul 5 10:03 Templates
25.11. Groups in NTFS acls
We have users on Unix, we have groups on Unix that contain those users.
[root@RHEL4b samba]# grep nt /etc/group
...
ntadmins:x:506:Administrator
ntsports:x:507:Venus,Serena,Kim,Figo,Pfaff
nttennis:x:508:Venus,Serena,Kim
ntfootball:x:509:Figo,Pfaff
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samba domain controller
[root@RHEL4b samba]#
We already added Venus to the tdbsam with smbpasswd.
smbpasswd -a Venus
Does this mean that Venus can access the tennis and the sports shares ? Yes, all access
works fine on the Samba server. But the nttennis group is not available on the windows
machines. To make the groups available on windows (like in the ntfs security tab of files
and folders), we have to map unix groups to windows groups. To do this, we use the net
groupmap command.
[root@RHEL4b samba]# net groupmap add ntgroup="tennis" unixgroup=nttennis type=d
No rid or sid specified, choosing algorithmic mapping
Successully added group tennis to the mapping db
[root@RHEL4b samba]# net groupmap add ntgroup="football" unixgroup=ntfootball type=d
No rid or sid specified, choosing algorithmic mapping
Successully added group football to the mapping db
[root@RHEL4b samba]# net groupmap add ntgroup="sports" unixgroup=ntsports type=d
No rid or sid specified, choosing algorithmic mapping
Successully added group sports to the mapping db
[root@RHEL4b samba]#
Now you can use the Samba groups on all NTFS volumes on members of the domain.
25.12. logon scripts
Before testing a logon script, make sure it has the proper carriage returns that DOS files have.
[root@RHEL4b netlogon]# cat start.bat
net use Z: \\DCSPORTS0\SPORTS
[root@RHEL4b netlogon]# unix2dos start.bat
unix2dos: converting file start.bat to DOS format ...
[root@RHEL4b netlogon]#
Then copy the scripts to the netlogon share, and add the following parameter to smb.conf.
logon script = start.bat
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samba domain controller
25.13. practice: samba domain controller
1. Setup Samba as a domain controller.
2. Create the shares salesdata, salespresentations and meetings. Salesdata must be accessible
to all sales people and to all managers. SalesPresentations is only for all sales people.
Meetings is only accessible to all managers. Use groups to accomplish this.
3. Join a Microsoft computer to your domain. Verify the creation of a computer account
in /etc/passwd.
4. Setup and verify the proper working of roaming profiles.
5. Find information about home directories for users, set them up and verify that users receive
their home directory mapped under the H:-drive in MS Windows Explorer.
6. Use a couple of samba domain groups with members to set acls on ntfs. Verify that it
works!
7. Knowing that the %m variable contains the computername, create a separate log file for
every computer(account).
8. Knowing that %s contains the client operating system, include a smb.%s.conf file that
contains a share. (The share will only be visible to clients with that OS).
9. If time permits (or if you are waiting for other students to finish this practice), then
combine "valid users" and "invalid users" with groups and usernames with "hosts allow"
and "hosts deny" and make a table of which get priority over which.
253
Chapter 26. a brief look at samba 4
254
a brief look at samba 4
255
a brief look at samba 4
26.1. Samba 4 alpha 6
A quick view on Samba 4 alpha 6 (January 2009). You can also follow this guide http://
wiki.samba.org/index.php/Samba4/HOWTO
Remove old Samba from Red Hat
yum remove samba
set a fix ip address (Red Hat has an easy GUI)
download and untar
samba.org, click 'download info', choose mirror, dl samba4 latest alpha
once untarred, enter the directory and read the howto4.txt
cd samba-4.0.0alpha6/
more howto4.txt
first we have to configure, compile and install samba4
cd source4/
./configure
make
make install
Then we can use the provision script to setup our realm. I used booi.schot as domain name
(instead of example.com).
./setup/provision --realm=BOOI.SCHOT --domain=BOOI --adminpass=stargate \
--server-role='domain controller'
i added a simple share for testing
vi /usr/local/samba/etc/smb.conf
then i started samba
cd /usr/local/samba/sbin/
./samba
I tested with smbclient, it works
smbclient //localhost/test -Uadministrator%stargate
I checked that bind (and bind-chroot) were installed (yes), so copied the srv records
cp booi.schot.zone /var/named/chroot/etc/
then appended to named.conf
cat named.conf >> /var/named/chroot/etc/named.conf
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a brief look at samba 4
I followed these steps in the howto4.txt
vi /etc/init.d/named [added two export lines right after start()]
chmod a+r /usr/local/samba/private/dns.keytab
cp krb5.conf /etc/
vi /var/named/chroot/etc/named.conf
--> remove a lot, but keep allow-update { any; };
restart bind (named!), then tested dns with dig, this works (stripped screenshot!)
[root@RHEL52 private]# dig _ldap._tcp.dc._msdcs.booi.schot SRV @localhost
; (1 server found)
;; global options: printcmd
;; Got answer:
;; -HEADER- opcode: QUERY, status: NXDOMAIN, id: 58186
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
;; QUESTION SECTION:
;_ldap._tcp.dc._msdcs.booi.schot. IN SRV
;; AUTHORITY SECTION:
. 10800 IN SOA A.ROOT-SERVERS.NET....
;; Query time: 54 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Tue Jan 27 20:57:05 2009
;; MSG SIZE rcvd: 124
[root@RHEL52 private]#
made sure /etc/resolv.conf points to himself
[root@RHEL52 private]# cat /etc/resolv.conf
search booi.schot
nameserver 127.0.0.1
start windows 2003 server, enter the samba4 as DNS!
ping the domain, if it doesn't work, then add your redhats hostname and your realm to
windows/system32/drivers/etc/hosts
join the windows computer to the domain
reboot the windows
log on with administrator stargate
start run dsa.msc to manage samba4
create an OU, a user and a GPO, test that it works
257
Part VI. Appendix
Table of Contents
A. License .................................................................................................................................................... 260
259
Appendix A. License
GNU Free Documentation License
Version 1.3, 3 November 2008
Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.
0. PREAMBLE
The purpose of this License is to make a manual, textbook, or other
functional and useful document "free" in the sense of freedom: to
assure everyone the effective freedom to copy and redistribute it,
with or without modifying it, either commercially or noncommercially.
Secondarily, this License preserves for the author and publisher a way
to get credit for their work, while not being considered responsible
for modifications made by others.
This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense. It
complements the GNU General Public License, which is a copyleft
license designed for free software.
We have designed this License in order to use it for manuals for free
software, because free software needs free documentation: a free
program should come with manuals providing the same freedoms that the
software does. But this License is not limited to software manuals; it
can be used for any textual work, regardless of subject matter or
whether it is published as a printed book. We recommend this License
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version if the original publisher of that version gives permission.
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* B. List on the Title Page, as authors, one or more persons or
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8. TRANSLATION
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10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of the
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11. RELICENSING
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The operator of an MMC Site may republish an MMC contained in the site
under CC-BY-SA on the same site at any time before August 1, 2009,
provided the MMC is eligible for relicensing.
266
block device, 37
Index browsable (Samba), 233
browseable (Samba), 233
browser master, 247
Symbols btrfs, 63
/bin/dmesg, 40 bzip2(1), 162
/dev, 51
/dev/hdX, 38
/dev/ht, 161
C
cable select, 36
/dev/nst, 161
char(mysql), 177
/dev/sdb, 92
character device, 37
/dev/sdX, 38
chattr(1), 165
/dev/st, 161
chgrp(1), 5
/etc/filesystems, 64, 71
chmod, 10
/etc/fstab, 22, 67, 75, 92
chmod(1), 9
/etc/group, 4, 173
chmod +x, 11
/etc/inetd.conf, 203
chown(1), 5
/etc/init.d/samba, 192
chroot, 84
/etc/init.d/smb, 192
CHS, 37
/etc/init.d/winbind, 193
CIFS, 194
/etc/lvm/.cache, 117
cpio(1), 165
/etc/mtab, 72
create(mysql), 175, 177, 183
/etc/nsswitch.conf, 241, 243
create mask (Samba), 233
/etc/passwd, 4, 173, 250
cylinder, 36
/etc/raidtab, 100
/etc/samba/passdb.tdb, 249
/etc/samba/smb.conf, 197, 198, 199, 215, 239 D
/etc/samba/smbpasswd, 220, 247 dd(1), 55, 166
/etc/shadow, 17 delete(mysql), 182
/etc/xinetd.d/swat, 203 deny hosts (Samba), 233
/proc/devices, 51, 51 describe(mysql), 178
/proc/filesystems, 64, 71 device driver, 51
/proc/mdstat, 100 devices.txt, 51
/proc/mounts, 72 df(1), 73, 73
/proc/partitions, 51 df -i, 26
/proc/scsi/scsi, 43 directory, 27, 61
/tmp, 16 directory mask (Samba), 233
/usr/bin/getfacl, 22 directory security mask(samba), 234
/usr/bin/passwd, 17 disk platters, 36
/usr/bin/setfacl, 22 dmesg(1), 40
.. (directory), 27 dpkg, 189
. (directory), 27 dpkg(1), 172
.my.cnf, 174 drop(mysql), 176, 178, 184
777, 10 du(1), 73
dump(1), 165
A
access control list, 22 E
access time, 36 e2fsck(1), 67
acl, 24 eiciel, 24
acls, 22 el torito, 63
allow hosts (Samba), 232 ext2, 62, 65
aptitude, 189, 190 ext3, 62
aptitude(8), 172 extended partition, 50
ata, 36
atapi, 36 F
fat16, 63
B fat32, 63
badblocks(8), 44 fd (partition type), 99
267
Index
fdisk, 139 L
fdisk(1), 51, 53, 54, 99
LAMP, 171
fdisk(8), 39
LBA, 37
fdisk limitations, 56
ln, 29
file ownership, 4
ln(1), 28
file system, 60
logical drive, 50
find(1), 16, 17, 28
logical drives, 55
force create mode(samba), 234
ls, 7, 26
force directory mode(samba), 234
ls(1), 26, 27
force directory security mode(samba), 234
ls -l, 6
force group(samba), 221
lsof, 82
force security mode(samba), 234
lsscsi(1), 42
force user(samba), 221
lvcreate(1), 107, 109, 123
fsck(1), 67
lvdisplay(1), 110, 118
fuser, 83, 83
lvextend(1), 110, 124
lvm, 84
G LVM, 104
getent(1), 242 lvmdiskscan(1), 115
getfacl, 22 lvol0, 123
gpt, 56 lvremove(1), 123
grant(mysql), 176 lvrename(1), 124
group by(mysql), 182 lvs(1), 118
guest ok (Samba), 208 lvscan(1), 118
gzip(1), 162
M
H major number, 51
hard link, 28 master (hard disk device), 36
hdparm(8), 45 master boot record, 55
head (hard disk device), 36 mbr, 55, 55, 56
hide unreadable (Samba), 233 MBR, 166
hostname, 194 mdadm(1), 100
hosts allow (Samba), 232 minor number, 51
hosts deny (Samba), 233 mirror, 97
mkdir, 71
I mkdir(1), 11
mke2fs(1), 62, 65, 109
IBM, 194
mkfs, 26
ide, 51
mkfs(1), 62, 65
idmap gid(samba), 239
mkinitrd(1), 62
idmap uid(samba), 239
mknod(1), 161
inetd(8), 203
mount, 71
initiator(iSCSI), 131
mount(1), 70, 72
inode, 25, 28
mounting, 70
inode table, 26
mount point, 70
insert(mysql), 179
mt(1), 161
integer(mysql), 177
multipath, 151
invalid users (Samba), 232
mysql, 171, 173, 174, 175
iostat, 85
mysql(group), 173
iotop, 86
mysql(user), 173
iSCSI, 131
mysql-client, 172
iscsiadm, 138
mysqld, 173
iso9660, 63, 166
mysql-server, 172
J N
jbod, 97 NetBIOS names, 194
joliet, 63 netcat, 211
journaling, 62 net groupmap, 252
268
Index
net rpc join(samba), 240 sata, 36
net use(microsoft), 210, 215, 226 scsi, 36
net view(microsoft), 197, 202 scsi id, 36
nmbd(8), 193 sector, 36
noacl(mount), 76 security(Samba), 208
nodev, 64, 71 security mask(samba), 234
noexec(mount), 76 security mode(samba), 225
nosuid(mount), 76 seek time, 36
NT_STATUS_BAD_NETWORK_NAME, 227 select(mysql), 179, 180, 180
NT_STATUS_LOGON_FAILURE, 227 service(8), 192
setfacl, 22
O setgid, 16, 16
octal permissions, 10 setuid, 17, 17, 17, 76
order by(mysql), 181 sfdisk(1), 55
owner, 7 show(mysql), 175, 177
slave (hard disk device), 36
SMB, 194
P smbclient, 200, 209
Parallel ATA, 36
smbclient(1), 199, 226
parity(raid), 97
smbd(8), 193, 197, 220
parted, 56, 57
smbpasswd(1), 252
parted(1), 53
smbpasswd(8), 220, 225
partition, 50
smbtree, 202
partition table, 55, 55
smbtree(1), 201
partprobe(1), 55
soft link, 29
passdb backend (Samba), 221
solid state drive, 37
passwd(1), 17
split(1), 167
php, 171
SQL, 171, 179
primary partition, 50
ssd, 37
pvchange(1), 120
sticky bit, 16
pvcreate(1), 107, 109, 119
striped disk, 97
pvdisplay(1), 109, 116
swap partition, 63
pvmove(1), 120
swat(8), 203
pvremove(1), 119
symbolic link, 29
pvresize(1), 119
pvs(1), 115
pvscan(1), 115 T
tar(1), 162, 163
R tdbsam, 221, 247, 249
testparm(1), 198, 198, 199
RAID, 96
track, 36
raid 1, 97
trigger(mysql), 183
read list (Samba), 232
triggers(mysql), 172
read only (Samba), 215
tune2fs(1), 62, 66, 91
reiserfs, 63
resize2fs(1), 110
restore(1), 165 U
rm(1), 29 udf, 63
roaming profiles(samba), 251 uefi, 56
rock ridge, 63 umask(1), 11
root(mysql), 172 universally unique identifier, 90
rotational latency, 36 update(mysql), 180
rpm, 189 use(mysql), 176
rpm(1), 172 uuid, 90
rpm(8), 190
rsyslog, 82 V
valid users (Samba), 232
S varchar(mysql), 177
samba, 189 vfat, 63
269
Index
vgchange(1), 122
vgcreate(1), 107, 109, 121
vgdisplay(1), 117
vgextend(1), 121
vgmerge(1), 122
vgreduce(1), 121
vgremove(1), 121
vgs(1), 117
vgscan(1), 117
vmstat, 87
vol_id(1), 91
W
wbinfo(1), 241, 242
winbind(8), 241
winbind(samba), 239
winbindd(8), 193, 193, 241
workgroup, 208
writable (Samba), 215
write list (Samba), 232
X
xinetd(8), 203
Y
yum, 190
Z
zfs, 63
270