Plaintext
Linux Servers
Paul Cobbaut
Linux Servers
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.eu, build scripts and infrastructure setup
• Ywein Van den Brande: ywein@crealaw.eu, license and legal sections
• Hendrik De Vloed: hendrik.devloed@ugent.be, buildheader.pl script
We'd also like to thank our reviewers:
• Wouter Verhelst: wo@uter.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://blog.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. apache and squid .......................................................................................................................................... 1
1. apache web server ............................................................................................................................ 3
1.1. introduction to apache ........................................................................................................... 4
1.2. port virtual hosts on Debian ................................................................................................ 11
1.3. named virtual hosts on Debian ........................................................................................... 15
1.4. password protected website on Debian ............................................................................... 17
1.5. port virtual hosts on CentOS .............................................................................................. 18
1.6. named virtual hosts on CentOS .......................................................................................... 22
1.7. password protected website on CentOS .............................................................................. 24
1.8. troubleshooting apache ........................................................................................................ 26
1.9. virtual hosts example ........................................................................................................... 27
1.10. aliases and redirects ........................................................................................................... 27
1.11. more on .htaccess ............................................................................................................... 27
1.12. traffic .................................................................................................................................. 27
1.13. self signed cert on Debian ................................................................................................ 28
1.14. self signed cert on RHEL/CentOS .................................................................................... 30
1.15. practice: apache ................................................................................................................. 32
2. introduction to squid ..................................................................................................................... 33
2.1. about proxy servers ............................................................................................................. 33
2.2. installing squid .................................................................................................................... 34
2.3. port 3128 .............................................................................................................................. 34
2.4. starting and stopping ........................................................................................................... 34
2.5. client proxy settings ............................................................................................................ 35
2.6. upside down images ............................................................................................................ 37
2.7. /var/log/squid ........................................................................................................................ 39
2.8. access control ...................................................................................................................... 39
2.9. testing squid ......................................................................................................................... 39
2.10. name resolution ................................................................................................................. 39
II. mysql database .......................................................................................................................................... 41
3. introduction to sql using mysql .................................................................................................... 43
3.1. installing mysql ................................................................................................................... 44
3.2. accessing mysql ................................................................................................................... 45
3.3. mysql databases ................................................................................................................... 47
3.4. mysql tables ......................................................................................................................... 49
3.5. mysql records ...................................................................................................................... 51
3.6. joining two tables ................................................................................................................ 54
3.7. mysql triggers ...................................................................................................................... 55
III. dns server ................................................................................................................................................. 57
4. introduction to DNS ....................................................................................................................... 59
4.1. about dns .............................................................................................................................. 60
4.2. dns namespace ..................................................................................................................... 63
4.3. caching only servers ............................................................................................................ 68
4.4. authoritative dns servers ...................................................................................................... 71
4.5. primary and secondary ........................................................................................................ 71
4.6. zone transfers ....................................................................................................................... 71
4.7. master and slave .................................................................................................................. 73
4.8. SOA record .......................................................................................................................... 73
4.9. full or incremental zone transfers ....................................................................................... 74
4.10. DNS cache ......................................................................................................................... 75
4.11. forward lookup zone example ........................................................................................... 76
4.12. example: caching only DNS server .................................................................................. 77
4.13. example: caching only with forwarder ............................................................................. 79
4.14. example: primary authoritative server .............................................................................. 81
4.15. example: a DNS slave server ............................................................................................ 85
4.16. practice: dns ....................................................................................................................... 87
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4.17. solution: dns ...................................................................................................................... 88
5. advanced DNS ................................................................................................................................ 89
5.1. example: DNS round robin ................................................................................................. 90
5.2. DNS delegation ................................................................................................................... 91
5.3. example: DNS delegation ................................................................................................... 92
5.4. example: split-horizon dns .................................................................................................. 94
5.5. old dns topics ...................................................................................................................... 96
IV. dhcp server ............................................................................................................................................ 100
6. introduction to dhcp .................................................................................................................... 102
6.1. four broadcasts .................................................................................................................. 103
6.2. picturing dhcp .................................................................................................................... 104
6.3. installing a dhcp server ..................................................................................................... 105
6.4. dhcp server for RHEL/CentOS ......................................................................................... 105
6.5. client reservations .............................................................................................................. 106
6.6. example config files .......................................................................................................... 106
6.7. older example config files ................................................................................................. 107
6.8. advanced dhcp ................................................................................................................... 109
6.9. Practice: dhcp .................................................................................................................... 110
V. iptables firewall ...................................................................................................................................... 111
7. introduction to routers ................................................................................................................ 113
7.1. router or firewall ............................................................................................................... 114
7.2. packet forwarding .............................................................................................................. 114
7.3. packet filtering ................................................................................................................... 114
7.4. stateful ................................................................................................................................ 114
7.5. nat (network address translation) ...................................................................................... 115
7.6. pat (port address translation) ............................................................................................. 115
7.7. snat (source nat) ................................................................................................................ 115
7.8. masquerading ..................................................................................................................... 115
7.9. dnat (destination nat) ......................................................................................................... 115
7.10. port forwarding ................................................................................................................ 115
7.11. /proc/sys/net/ipv4/ip_forward .......................................................................................... 116
7.12. /etc/sysctl.conf .................................................................................................................. 116
7.13. sysctl ................................................................................................................................ 116
7.14. practice: packet forwarding ............................................................................................. 117
7.15. solution: packet forwarding ............................................................................................. 119
8. iptables firewall ............................................................................................................................ 122
8.1. iptables tables .................................................................................................................... 123
8.2. starting and stopping iptables ............................................................................................ 123
8.3. the filter table .................................................................................................................... 124
8.4. practice: packet filtering .................................................................................................... 129
8.5. solution: packet filtering ................................................................................................... 130
8.6. network address translation ............................................................................................... 131
VI. Introduction to Samba ........................................................................................................................... 134
9. introduction to samba .................................................................................................................. 137
9.1. verify installed version ...................................................................................................... 138
9.2. installing samba ................................................................................................................. 139
9.3. documentation .................................................................................................................... 140
9.4. starting and stopping samba .............................................................................................. 141
9.5. samba daemons .................................................................................................................. 142
9.6. the SMB protocol .............................................................................................................. 143
9.7. practice: introduction to samba ......................................................................................... 144
10. getting started with samba ........................................................................................................ 145
10.1. /etc/samba/smb.conf ......................................................................................................... 146
10.2. /usr/bin/testparm ............................................................................................................... 147
10.3. /usr/bin/smbclient ............................................................................................................. 148
10.4. /usr/bin/smbtree ................................................................................................................ 150
10.5. server string ..................................................................................................................... 151
10.6. Samba Web Administration Tool (SWAT) .................................................................... 152
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Linux Servers
10.7. practice: getting started with samba ................................................................................ 153
10.8. solution: getting started with samba ............................................................................... 154
11. a read only file server ................................................................................................................ 156
11.1. Setting up a directory to share ........................................................................................ 157
11.2. configure the share .......................................................................................................... 157
11.3. restart the server .............................................................................................................. 158
11.4. verify the share ................................................................................................................ 158
11.5. a note on netcat ............................................................................................................... 160
11.6. practice: read only file server ......................................................................................... 161
11.7. solution: read only file server ......................................................................................... 162
12. a writable file server .................................................................................................................. 163
12.1. set up a directory to share ............................................................................................... 164
12.2. share section in smb.conf ................................................................................................ 164
12.3. configure the share .......................................................................................................... 164
12.4. test connection with windows ......................................................................................... 164
12.5. test writing with windows ............................................................................................... 165
12.6. How is this possible ? ..................................................................................................... 165
12.7. practice: writable file server ............................................................................................ 166
12.8. solution: writable file server ........................................................................................... 167
13. samba first user account ........................................................................................................... 168
13.1. creating a samba user ...................................................................................................... 169
13.2. ownership of files ............................................................................................................ 169
13.3. /usr/bin/smbpasswd .......................................................................................................... 169
13.4. /etc/samba/smbpasswd ..................................................................................................... 169
13.5. passdb backend ................................................................................................................ 170
13.6. forcing this user ............................................................................................................... 170
13.7. practice: first samba user account ................................................................................... 171
13.8. solution: first samba user account ................................................................................... 172
14. samba authentication ................................................................................................................. 173
14.1. creating the users on Linux ............................................................................................. 174
14.2. creating the users on samba ............................................................................................ 174
14.3. security = user ................................................................................................................. 174
14.4. configuring the share ....................................................................................................... 175
14.5. testing access with net use .............................................................................................. 175
14.6. testing access with smbclient .......................................................................................... 175
14.7. verify ownership .............................................................................................................. 176
14.8. common problems ........................................................................................................... 176
14.9. practice : samba authentication ....................................................................................... 178
14.10. solution: samba authentication ...................................................................................... 179
15. samba securing shares ............................................................................................................... 180
15.1. security based on user name ........................................................................................... 181
15.2. security based on ip-address ........................................................................................... 181
15.3. security through obscurity ............................................................................................... 182
15.4. file system security .......................................................................................................... 182
15.5. practice: securing shares ................................................................................................. 184
15.6. solution: securing shares ................................................................................................. 185
16. samba domain member ............................................................................................................. 187
16.1. changes in smb.conf ........................................................................................................ 188
16.2. joining an Active Directory domain ............................................................................... 189
16.3. winbind ............................................................................................................................ 190
16.4. wbinfo .............................................................................................................................. 190
16.5. getent ................................................................................................................................ 191
16.6. file ownership .................................................................................................................. 192
16.7. practice : samba domain member .................................................................................... 193
17. samba domain controller ........................................................................................................... 194
17.1. about Domain Controllers ............................................................................................... 195
17.2. About security modes ...................................................................................................... 195
17.3. About password backends ............................................................................................... 196
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Linux Servers
17.4. [global] section in smb.conf ............................................................................................ 196
17.5. netlogon share .................................................................................................................. 197
17.6. other [share] sections ....................................................................................................... 197
17.7. Users and Groups ............................................................................................................ 198
17.8. tdbsam .............................................................................................................................. 198
17.9. about computer accounts ................................................................................................. 199
17.10. local or roaming profiles ............................................................................................... 199
17.11. Groups in NTFS acls ..................................................................................................... 200
17.12. logon scripts .................................................................................................................. 201
17.13. practice: samba domain controller ................................................................................ 202
18. a brief look at samba 4 ............................................................................................................. 203
18.1. Samba 4 alpha 6 .............................................................................................................. 205
VII. selinux .................................................................................................................................................. 207
19. introduction to SELinux ............................................................................................................ 209
19.1. selinux modes .................................................................................................................. 210
19.2. logging ............................................................................................................................. 210
19.3. activating selinux ............................................................................................................. 210
19.4. getenforce ......................................................................................................................... 211
19.5. setenforce ......................................................................................................................... 211
19.6. sestatus ............................................................................................................................. 212
19.7. policy ............................................................................................................................... 212
19.8. /etc/selinux/config ............................................................................................................ 212
19.9. DAC or MAC .................................................................................................................. 213
19.10. ls -Z ............................................................................................................................... 213
19.11. -Z .................................................................................................................................... 213
19.12. /selinux ........................................................................................................................... 214
19.13. identity ........................................................................................................................... 214
19.14. role ................................................................................................................................. 214
19.15. type (or domain) ............................................................................................................ 215
19.16. security context .............................................................................................................. 216
19.17. transition ........................................................................................................................ 216
19.18. extended attributes ......................................................................................................... 217
19.19. process security context ................................................................................................ 217
19.20. chcon .............................................................................................................................. 217
19.21. an example ..................................................................................................................... 218
19.22. setroubleshoot ................................................................................................................ 220
19.23. booleans ......................................................................................................................... 222
VIII. introducing git ..................................................................................................................................... 223
20. git ................................................................................................................................................. 225
20.1. git ..................................................................................................................................... 226
20.2. installing git ..................................................................................................................... 227
20.3. starting a project .............................................................................................................. 227
20.4. git branches ...................................................................................................................... 230
20.5. to be continued... ............................................................................................................. 231
20.6. github.com ....................................................................................................................... 232
20.7. add your public key to github ......................................................................................... 232
20.8. practice: git ...................................................................................................................... 233
IX. ipv6 ........................................................................................................................................................ 234
21. Introduction to ipv6 ................................................................................................................... 236
21.1. about ipv6 ........................................................................................................................ 237
21.2. network id and host id .................................................................................................... 237
21.3. host part generation ......................................................................................................... 237
21.4. ipv4 mapped ipv6 address ............................................................................................... 238
21.5. link local addresses ......................................................................................................... 238
21.6. unique local addresses ..................................................................................................... 238
21.7. globally unique unicast addresses ................................................................................... 238
21.8. 6to4 .................................................................................................................................. 238
21.9. ISP .................................................................................................................................... 239
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Linux Servers
21.10. non routable addresses .................................................................................................. 239
21.11. ping6 .............................................................................................................................. 239
21.12. Belgium and ipv6 .......................................................................................................... 240
21.13. other websites ................................................................................................................ 240
21.14. 6to4 gateways ................................................................................................................ 242
21.15. ping6 and dns ................................................................................................................ 242
21.16. ipv6 and tcp/http ............................................................................................................ 242
21.17. ipv6 PTR record ............................................................................................................ 242
21.18. 6to4 setup on Linux ...................................................................................................... 242
X. Appendices .............................................................................................................................................. 245
A. cloning ........................................................................................................................................... 247
A.1. About cloning ................................................................................................................... 247
A.2. About offline cloning ....................................................................................................... 247
A.3. Offline cloning example ................................................................................................... 247
B. License .......................................................................................................................................... 249
Index ............................................................................................................................................................. 256
vii
List of Tables
4.1. the first top level domains ..................................................................................................................... 65
4.2. new general purpose tld's ....................................................................................................................... 65
7.1. Packet Forwarding Exercise ................................................................................................................. 117
7.2. Packet Forwarding Solution ................................................................................................................. 119
viii
Part I. apache and squid
Table of Contents
1. apache web server ..................................................................................................................................... 3
1.1. introduction to apache ..................................................................................................................... 4
1.2. port virtual hosts on Debian ......................................................................................................... 11
1.3. named virtual hosts on Debian ..................................................................................................... 15
1.4. password protected website on Debian ........................................................................................ 17
1.5. port virtual hosts on CentOS ........................................................................................................ 18
1.6. named virtual hosts on CentOS .................................................................................................... 22
1.7. password protected website on CentOS ....................................................................................... 24
1.8. troubleshooting apache ................................................................................................................. 26
1.9. virtual hosts example .................................................................................................................... 27
1.10. aliases and redirects .................................................................................................................... 27
1.11. more on .htaccess ........................................................................................................................ 27
1.12. traffic ........................................................................................................................................... 27
1.13. self signed cert on Debian .......................................................................................................... 28
1.14. self signed cert on RHEL/CentOS ............................................................................................. 30
1.15. practice: apache ........................................................................................................................... 32
2. introduction to squid ............................................................................................................................... 33
2.1. about proxy servers ....................................................................................................................... 33
2.2. installing squid .............................................................................................................................. 34
2.3. port 3128 ....................................................................................................................................... 34
2.4. starting and stopping ..................................................................................................................... 34
2.5. client proxy settings ...................................................................................................................... 35
2.6. upside down images ...................................................................................................................... 37
2.7. /var/log/squid ................................................................................................................................. 39
2.8. access control ................................................................................................................................ 39
2.9. testing squid .................................................................................................................................. 39
2.10. name resolution ........................................................................................................................... 39
2
Chapter 1. apache web server
In this chapter we learn how to setup a web server with the apache software.
According to NetCraft (http://news.netcraft.com/archives/web_server_survey.html) about
seventy percent of all web servers are running on Apache. The name is derived from a
patchy web server, because of all the patches people wrote for the NCSA httpd server.
Later chapters will expand this web server into a LAMP stack (Linux, Apache, Mysql, Perl/
PHP/Python).
3
apache web server
1.1. introduction to apache
1.1.1. installing on Debian
This screenshot shows that there is no apache server installed, nor does the /var/www
directory exist.
root@debian7:~# ls -l /var/www
ls: cannot access /var/www: No such file or directory
root@debian7:~# dpkg -l | grep apache
To install apache on Debian:
root@debian7:~# aptitude install apache2
The following NEW packages will be installed:
apache2 apache2-mpm-worker{a} apache2-utils{a} apache2.2-bin{a} apache2.2-com\
mon{a} libapr1{a} libaprutil1{a} libaprutil1-dbd-sqlite3{a} libaprutil1-ldap{a}\
ssl-cert{a}
0 packages upgraded, 10 newly installed, 0 to remove and 0 not upgraded.
Need to get 1,487 kB of archives. After unpacking 5,673 kB will be used.
Do you want to continue? [Y/n/?]
After installation, the same two commands as above will yield a different result:
root@debian7:~# ls -l /var/www
total 4
-rw-r--r-- 1 root root 177 Apr 29 11:55 index.html
root@debian7:~# dpkg -l | grep apache | tr -s ' '
ii apache2 2.2.22-13+deb7u1 amd64 Apache HTTP Server metapackage
ii apache2-mpm-worker 2.2.22-13+deb7u1 amd64 Apache HTTP Server - high speed th\
readed model
ii apache2-utils 2.2.22-13+deb7u1 amd64 utility programs for webservers
ii apache2.2-bin 2.2.22-13+deb7u1 amd64 Apache HTTP Server common binary files
ii apache2.2-common 2.2.22-13+deb7u1 amd64 Apache HTTP Server common files
4
apache web server
1.1.2. installing on RHEL/CentOS
Note that Red Hat derived distributions use httpd as package and process name instead of
apache.
To verify whether apache is installed in CentOS/RHEL:
[root@centos65 ~]# rpm -q httpd
package httpd is not installed
[root@centos65 ~]# ls -l /var/www
ls: cannot access /var/www: No such file or directory
To install apache on CentOS:
[root@centos65 ~]# yum install httpd
After running the yum install httpd command, the Centos 6.5 server has apache installed
and the /var/www directory exists.
[root@centos65 ~]# rpm -q httpd
httpd-2.2.15-30.el6.centos.x86_64
[root@centos65 ~]# ls -l /var/www
total 16
drwxr-xr-x. 2 root root 4096 Apr 3 23:57 cgi-bin
drwxr-xr-x. 3 root root 4096 May 6 13:08 error
drwxr-xr-x. 2 root root 4096 Apr 3 23:57 html
drwxr-xr-x. 3 root root 4096 May 6 13:08 icons
[root@centos65 ~]#
5
apache web server
1.1.3. running apache on Debian
This is how you start apache2 on Debian.
root@debian7:~# service apache2 status
Apache2 is NOT running.
root@debian7:~# service apache2 start
Starting web server: apache2apache2: Could not reliably determine the server's \
fully qualified domain name, using 127.0.1.1 for ServerName
.
To verify, run the service apache2 status command again or use ps.
root@debian7:~# service apache2 status
Apache2 is running (pid 3680).
root@debian7:~# ps -C apache2
PID TTY TIME CMD
3680 ? 00:00:00 apache2
3683 ? 00:00:00 apache2
3684 ? 00:00:00 apache2
3685 ? 00:00:00 apache2
root@debian7:~#
Or use wget and file to verify that your web server serves an html document.
root@debian7:~# wget 127.0.0.1
--2014-05-06 13:27:02-- http://127.0.0.1/
Connecting to 127.0.0.1:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 177 [text/html]
Saving to: `index.html'
100%[==================================================>] 177 --.-K/s in 0s
2014-05-06 13:27:02 (15.8 MB/s) - `index.html' saved [177/177]
root@debian7:~# file index.html
index.html: HTML document, ASCII text
root@debian7:~#
Or verify that apache is running by opening a web browser, and browse to the ip-address of
your server. An Apache test page should be shown.
You can do the following to quickly avoid the 'could not reliably determine the fqdn' message
when restarting apache.
root@debian7:~# echo ServerName Debian7 >> /etc/apache2/apache2.conf
root@debian7:~# service apache2 restart
Restarting web server: apache2 ... waiting .
root@debian7:~#
6
apache web server
1.1.4. running apache on CentOS
Starting the httpd on RHEL/CentOS is done with the service command.
[root@centos65 ~]# service httpd status
httpd is stopped
[root@centos65 ~]# service httpd start
Starting httpd: httpd: Could not reliably determine the server's fully qualifie\
d domain name, using 127.0.0.1 for ServerName
[ OK ]
[root@centos65 ~]#
To verify that apache is running, use ps or issue the service httpd status command again.
[root@centos65 ~]# service httpd status
httpd (pid 2410) is running...
[root@centos65 ~]# ps -C httpd
PID TTY TIME CMD
2410 ? 00:00:00 httpd
2412 ? 00:00:00 httpd
2413 ? 00:00:00 httpd
2414 ? 00:00:00 httpd
2415 ? 00:00:00 httpd
2416 ? 00:00:00 httpd
2417 ? 00:00:00 httpd
2418 ? 00:00:00 httpd
2419 ? 00:00:00 httpd
[root@centos65 ~]#
To prevent the 'Could not reliably determine the fqdn' message, issue the following
command.
[root@centos65 ~]# echo ServerName Centos65 >> /etc/httpd/conf/httpd.conf
[root@centos65 ~]# service httpd restart
Stopping httpd: [ OK ]
Starting httpd: [ OK ]
[root@centos65 ~]#
7
apache web server
1.1.5. index file on CentOS
CentOS does not provide a standard index.html or index.php file. A simple wget gives an
error.
[root@centos65 ~]# wget 127.0.0.1
--2014-05-06 15:10:22-- http://127.0.0.1/
Connecting to 127.0.0.1:80... connected.
HTTP request sent, awaiting response... 403 Forbidden
2014-05-06 15:10:22 ERROR 403: Forbidden.
Instead when visiting the ip-address of your server in a web browser you get a noindex.html
page. You can verify this using wget.
[root@centos65 ~]# wget http://127.0.0.1/error/noindex.html
--2014-05-06 15:16:05-- http://127.0.0.1/error/noindex.html
Connecting to 127.0.0.1:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 5039 (4.9K) [text/html]
Saving to: “noindex.html”
100%[=============================================>] 5,039 --.-K/s in 0s
2014-05-06 15:16:05 (289 MB/s) - “noindex.html” saved [5039/5039]
[root@centos65 ~]# file noindex.html
noindex.html: HTML document text
[root@centos65 ~]#
Any custom index.html file in /var/www/html will immediately serve as an index for this
web server.
[root@centos65 ~]# echo 'Welcome to my website' > /var/www/html/index.html
[root@centos65 ~]# wget http://127.0.0.1
--2014-05-06 15:19:16-- http://127.0.0.1/
Connecting to 127.0.0.1:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 22 [text/html]
Saving to: “index.html”
100%[=============================================>] 22 --.-K/s in 0s
2014-05-06 15:19:16 (1.95 MB/s) - “index.html” saved [22/22]
[root@centos65 ~]# cat index.html
Welcome to my website
8
apache web server
1.1.6. default website
Changing the default website of a freshly installed apache web server is easy. All you need
to do is create (or change) an index.html file in the DocumentRoot directory.
To locate the DocumentRoot directory on Debian:
root@debian7:~# grep DocumentRoot /etc/apache2/sites-available/default
DocumentRoot /var/www
This means that /var/www/index.html is the default web site.
root@debian7:~# cat /var/www/index.html
<html><body><h1>It works!</h1>
<p>This is the default web page for this server.</p>
<p>The web server software is running but no content has been added, yet.</p>
</body></html>
root@debian7:~#
This screenshot shows how to locate the DocumentRoot directory on RHEL/CentOS.
[root@centos65 ~]# grep ^DocumentRoot /etc/httpd/conf/httpd.conf
DocumentRoot "/var/www/html"
RHEL/CentOS have no default web page (only the noindex.html error page mentioned
before). But an index.html file created in /var/www/html/ will automatically be used as
default page.
[root@centos65 ~]# echo '<html><head><title>Default website</title></head><body\
><p>A new web page</p></body></html>' > /var/www/html/index.html
[root@centos65 ~]# cat /var/www/html/index.html
<html><head><title>Default website</title></head><body><p>A new web page</p></b\
ody></html>
[root@centos65 ~]#
9
apache web server
1.1.7. apache configuration
There are many similarities, but also a couple of differences when configuring apache on
Debian or on CentOS. Both Linux families will get their own chapters with examples.
All configuration on RHEL/CentOS is done in /etc/httpd.
[root@centos65 ~]# ls -l /etc/httpd/
total 8
drwxr-xr-x. 2 root root 4096 May 6 13:08 conf
drwxr-xr-x. 2 root root 4096 May 6 13:08 conf.d
lrwxrwxrwx. 1 root root 19 May 6 13:08 logs -> ../../var/log/httpd
lrwxrwxrwx. 1 root root 29 May 6 13:08 modules -> ../../usr/lib64/httpd/modu\
les
lrwxrwxrwx. 1 root root 19 May 6 13:08 run -> ../../var/run/httpd
[root@centos65 ~]#
Debian (and ubuntu/mint/...) use /etc/apache2.
root@debian7:~# ls -l /etc/apache2/
total 72
-rw-r--r-- 1 root root 9659 May 6 14:23 apache2.conf
drwxr-xr-x 2 root root 4096 May 6 13:19 conf.d
-rw-r--r-- 1 root root 1465 Jan 31 18:35 envvars
-rw-r--r-- 1 root root 31063 Jul 20 2013 magic
drwxr-xr-x 2 root root 4096 May 6 13:19 mods-available
drwxr-xr-x 2 root root 4096 May 6 13:19 mods-enabled
-rw-r--r-- 1 root root 750 Jan 26 12:13 ports.conf
drwxr-xr-x 2 root root 4096 May 6 13:19 sites-available
drwxr-xr-x 2 root root 4096 May 6 13:19 sites-enabled
root@debian7:~#
10
apache web server
1.2. port virtual hosts on Debian
1.2.1. default virtual host
Debian has a virtualhost configuration file for its default website in /etc/apache2/sites-
available/default.
root@debian7:~# head -2 /etc/apache2/sites-available/default
<VirtualHost *:80>
ServerAdmin webmaster@localhost
1.2.2. three extra virtual hosts
In this scenario we create three additional websites for three customers that share a clubhouse
and want to jointly hire you. They are a model train club named Choo Choo, a chess club
named Chess Club 42 and a hackerspace named hunter2.
One way to put three websites on one web server, is to put each website on a different port.
This screenshot shows three newly created virtual hosts, one for each customer.
root@debian7:~# vi /etc/apache2/sites-available/choochoo
root@debian7:~# cat /etc/apache2/sites-available/choochoo
<VirtualHost *:7000>
ServerAdmin webmaster@localhost
DocumentRoot /var/www/choochoo
</VirtualHost>
root@debian7:~# vi /etc/apache2/sites-available/chessclub42
root@debian7:~# cat /etc/apache2/sites-available/chessclub42
<VirtualHost *:8000>
ServerAdmin webmaster@localhost
DocumentRoot /var/www/chessclub42
</VirtualHost>
root@debian7:~# vi /etc/apache2/sites-available/hunter2
root@debian7:~# cat /etc/apache2/sites-available/hunter2
<VirtualHost *:9000>
ServerAdmin webmaster@localhost
DocumentRoot /var/www/hunter2
</VirtualHost>
Notice the different port numbers 7000, 8000 and 9000. Notice also that we specified a
unique DocumentRoot for each website.
Are you using Ubuntu or Mint, then these configfiles need to end in .conf.
11
apache web server
1.2.3. three extra ports
We need to enable these three ports on apache in the ports.conf file. Open this file with vi
and add three lines to listen on three extra ports.
root@debian7:~# vi /etc/apache2/ports.conf
Verify with grep that the Listen directives are added correctly.
root@debian7:~# grep ^Listen /etc/apache2/ports.conf
Listen 80
Listen 7000
Listen 8000
Listen 9000
1.2.4. three extra websites
Next we need to create three DocumentRoot directories.
root@debian7:~# mkdir /var/www/choochoo
root@debian7:~# mkdir /var/www/chessclub42
root@debian7:~# mkdir /var/www/hunter2
And we have to put some really simple website in those directories.
root@debian7:~# echo 'Choo Choo model train Choo Choo' > /var/www/choochoo/inde\
x.html
root@debian7:~# echo 'Welcome to chess club 42' > /var/www/chessclub42/index.ht\
ml
root@debian7:~# echo 'HaCkInG iS fUn At HuNtEr2' > /var/www/hunter2/index.html
12
apache web server
1.2.5. enabling extra websites
The last step is to enable the websites with the a2ensite command. This command will create
links in sites-enabled.
The links are not there yet...
root@debian7:~# cd /etc/apache2/
root@debian7:/etc/apache2# ls sites-available/
chessclub42 choochoo default default-ssl hunter2
root@debian7:/etc/apache2# ls sites-enabled/
000-default
So we run the a2ensite command for all websites.
root@debian7:/etc/apache2# a2ensite choochoo
Enabling site choochoo.
To activate the new configuration, you need to run:
service apache2 reload
root@debian7:/etc/apache2# a2ensite chessclub42
Enabling site chessclub42.
To activate the new configuration, you need to run:
service apache2 reload
root@debian7:/etc/apache2# a2ensite hunter2
Enabling site hunter2.
To activate the new configuration, you need to run:
service apache2 reload
The links are created, so we can tell apache.
root@debian7:/etc/apache2# ls sites-enabled/
000-default chessclub42 choochoo hunter2
root@debian7:/etc/apache2# service apache2 reload
Reloading web server config: apache2.
root@debian7:/etc/apache2#
13
apache web server
1.2.6. testing the three websites
Testing the model train club named Choo Choo on port 7000.
root@debian7:/etc/apache2# wget 127.0.0.1:7000
--2014-05-06 21:16:03-- http://127.0.0.1:7000/
Connecting to 127.0.0.1:7000... connected.
HTTP request sent, awaiting response... 200 OK
Length: 32 [text/html]
Saving to: `index.html'
100%[============================================>] 32 --.-K/s in 0s
2014-05-06 21:16:03 (2.92 MB/s) - `index.html' saved [32/32]
root@debian7:/etc/apache2# cat index.html
Choo Choo model train Choo Choo
Testing the chess club named Chess Club 42 on port 8000.
root@debian7:/etc/apache2# wget 127.0.0.1:8000
--2014-05-06 21:16:20-- http://127.0.0.1:8000/
Connecting to 127.0.0.1:8000... connected.
HTTP request sent, awaiting response... 200 OK
Length: 25 [text/html]
Saving to: `index.html.1'
100%[===========================================>] 25 --.-K/s in 0s
2014-05-06 21:16:20 (2.16 MB/s) - `index.html.1' saved [25/25]
root@debian7:/etc/apache2# cat index.html.1
Welcome to chess club 42
Testing the hacker club named hunter2 on port 9000.
root@debian7:/etc/apache2# wget 127.0.0.1:9000
--2014-05-06 21:16:30-- http://127.0.0.1:9000/
Connecting to 127.0.0.1:9000... connected.
HTTP request sent, awaiting response... 200 OK
Length: 26 [text/html]
Saving to: `index.html.2'
100%[===========================================>] 26 --.-K/s in 0s
2014-05-06 21:16:30 (2.01 MB/s) - `index.html.2' saved [26/26]
root@debian7:/etc/apache2# cat index.html.2
HaCkInG iS fUn At HuNtEr2
Cleaning up the temporary files.
root@debian7:/etc/apache2# rm index.html index.html.1 index.html.2
Try testing from another computer using the ip-address of your server.
14
apache web server
1.3. named virtual hosts on Debian
1.3.1. named virtual hosts
The chess club and the model train club find the port numbers too hard to remember. They
would prefere to have their website accessible by name.
We continue work on the same server that has three websites on three ports. We need to
make sure those websites are accesible using the names choochoo.local, chessclub42.local
and hunter2.local.
We start by creating three new virtualhosts.
root@debian7:/etc/apache2/sites-available# vi choochoo.local
root@debian7:/etc/apache2/sites-available# vi chessclub42.local
root@debian7:/etc/apache2/sites-available# vi hunter2.local
root@debian7:/etc/apache2/sites-available# cat choochoo.local
<VirtualHost *:80>
ServerAdmin webmaster@localhost
ServerName choochoo.local
DocumentRoot /var/www/choochoo
</VirtualHost>
root@debian7:/etc/apache2/sites-available# cat chessclub42.local
<VirtualHost *:80>
ServerAdmin webmaster@localhost
ServerName chessclub42.local
DocumentRoot /var/www/chessclub42
</VirtualHost>
root@debian7:/etc/apache2/sites-available# cat hunter2.local
<VirtualHost *:80>
ServerAdmin webmaster@localhost
ServerName hunter2.local
DocumentRoot /var/www/hunter2
</VirtualHost>
root@debian7:/etc/apache2/sites-available#
Notice that they all listen on port 80 and have an extra ServerName directive.
1.3.2. name resolution
We need some way to resolve names. This can be done with DNS, which is discussed in
another chapter. For this demo it is also possible to quickly add the three names to the /etc/
hosts file.
root@debian7:/etc/apache2/sites-available# grep ^192 /etc/hosts
192.168.42.50 choochoo.local
192.168.42.50 chessclub42.local
192.168.42.50 hunter2.local
Note that you may have another ip address...
15
apache web server
1.3.3. enabling virtual hosts
Next we enable them with a2ensite.
root@debian7:/etc/apache2/sites-available# a2ensite choochoo.local
Enabling site choochoo.local.
To activate the new configuration, you need to run:
service apache2 reload
root@debian7:/etc/apache2/sites-available# a2ensite chessclub42.local
Enabling site chessclub42.local.
To activate the new configuration, you need to run:
service apache2 reload
root@debian7:/etc/apache2/sites-available# a2ensite hunter2.local
Enabling site hunter2.local.
To activate the new configuration, you need to run:
service apache2 reload
1.3.4. reload and verify
After a service apache2 reload the websites should be available by name.
root@debian7:/etc/apache2/sites-available# service apache2 reload
Reloading web server config: apache2.
root@debian7:/etc/apache2/sites-available# wget chessclub42.local
--2014-05-06 21:37:13-- http://chessclub42.local/
Resolving chessclub42.local (chessclub42.local)... 192.168.42.50
Connecting to chessclub42.local (chessclub42.local)|192.168.42.50|:80... conne\
cted.
HTTP request sent, awaiting response... 200 OK
Length: 25 [text/html]
Saving to: `index.html'
100%[=============================================>] 25 --.-K/s in 0s
2014-05-06 21:37:13 (2.06 MB/s) - `index.html' saved [25/25]
root@debian7:/etc/apache2/sites-available# cat index.html
Welcome to chess club 42
16
apache web server
1.4. password protected website on Debian
You can secure files and directories in your website with a .htaccess file that refers to a
.htpasswd file. The htpasswd command can create a .htpasswd file that contains a userid
and an (encrypted) password.
This screenshot creates a user and password for the hacker named cliff and uses the -c flag
to create the .htpasswd file.
root@debian7:~# htpasswd -c /var/www/.htpasswd cliff
New password:
Re-type new password:
Adding password for user cliff
root@debian7:~# cat /var/www/.htpasswd
cliff:$apr1$vujll0KL$./SZ4w9q0swhX93pQ0PVp.
Hacker rob also wants access, this screenshot shows how to add a second user and password
to .htpasswd.
root@debian7:~# htpasswd /var/www/.htpasswd rob
New password:
Re-type new password:
Adding password for user rob
root@debian7:~# cat /var/www/.htpasswd
cliff:$apr1$vujll0KL$./SZ4w9q0swhX93pQ0PVp.
rob:$apr1$HNln1FFt$nRlpF0H.IW11/1DRq4lQo0
Both Cliff and Rob chose the same password (hunter2), but that is not visible in the
.htpasswd file because of the different salts.
Next we need to create a .htaccess file in the DocumentRoot of the website we want to
protect. This screenshot shows an example.
root@debian7:~# cd /var/www/hunter2/
root@debian7:/var/www/hunter2# cat .htaccess
AuthUserFile /var/www/.htpasswd
AuthName "Members only!"
AuthType Basic
require valid-user
Note that we are protecting the website on port 9000 that we created earlier.
And because we put the website for the Hackerspace named hunter2 in a subdirectory of the
default website, we will need to adjust the AllowOvveride parameter in /etc/apache2/sites-
available/default as this screenshot shows (with line numbers on Debian7, your may vary).
9 <Directory /var/www/>
10 Options Indexes FollowSymLinks MultiViews
11 AllowOverride Authconfig
12 Order allow,deny
13 allow from all
14 </Directory
Now restart the apache2 server and test that it works!
17
apache web server
1.5. port virtual hosts on CentOS
1.5.1. default virtual host
Unlike Debian, CentOS has no virtualHost configuration file for its default website. Instead
the default configuration will throw a standard error page when no index file can be found
in the default location (/var/www/html).
1.5.2. three extra virtual hosts
In this scenario we create three additional websites for three customers that share a clubhouse
and want to jointly hire you. They are a model train club named Choo Choo, a chess club
named Chess Club 42 and a hackerspace named hunter2.
One way to put three websites on one web server, is to put each website on a different port.
This screenshot shows three newly created virtual hosts, one for each customer.
[root@CentOS65 ~]# vi /etc/httpd/conf.d/choochoo.conf
[root@CentOS65 ~]# cat /etc/httpd/conf.d/choochoo.conf
<VirtualHost *:7000>
ServerAdmin webmaster@localhost
DocumentRoot /var/www/html/choochoo
</VirtualHost>
[root@CentOS65 ~]# vi /etc/httpd/conf.d/chessclub42.conf
[root@CentOS65 ~]# cat /etc/httpd/conf.d/chessclub42.conf
<VirtualHost *:8000>
ServerAdmin webmaster@localhost
DocumentRoot /var/www/html/chessclub42
</VirtualHost>
[root@CentOS65 ~]# vi /etc/httpd/conf.d/hunter2.conf
[root@CentOS65 ~]# cat /etc/httpd/conf.d/hunter2.conf
<VirtualHost *:9000>
ServerAdmin webmaster@localhost
DocumentRoot /var/www/html/hunter2
</VirtualHost>
Notice the different port numbers 7000, 8000 and 9000. Notice also that we specified a
unique DocumentRoot for each website.
1.5.3. three extra ports
We need to enable these three ports on apache in the httpd.conf file.
[root@CentOS65 ~]# vi /etc/httpd/conf/httpd.conf
root@debian7:~# grep ^Listen /etc/httpd/conf/httpd.conf
Listen 80
Listen 7000
Listen 8000
Listen 9000
18
apache web server
1.5.4. SELinux guards our ports
If we try to restart our server, we will notice the following error:
[root@CentOS65 ~]# service httpd restart
Stopping httpd: [ OK ]
Starting httpd:
(13)Permission denied: make_sock: could not bind to address 0.0.0.0:7000
no listening sockets available, shutting down
[FAILED]
This is due to SELinux reserving ports 7000 and 8000 for other uses. We need to tell SELinux
we want to use these ports for http traffic
[root@CentOS65 ~]# semanage port -m -t http_port_t -p tcp 7000
[root@CentOS65 ~]# semanage port -m -t http_port_t -p tcp 8000
[root@CentOS65 ~]# service httpd restart
Stopping httpd: [ OK ]
Starting httpd: [ OK ]
1.5.5. three extra websites
Next we need to create three DocumentRoot directories.
[root@CentOS65 ~]# mkdir /var/www/html/choochoo
[root@CentOS65 ~]# mkdir /var/www/html/chessclub42
[root@CentOS65 ~]# mkdir /var/www/html/hunter2
And we have to put some really simple website in those directories.
[root@CentOS65 ~]# echo 'Choo Choo model train Choo Choo' > /var/www/html/chooc\
hoo/index.html
[root@CentOS65 ~]# echo 'Welcome to chess club 42' > /var/www/html/chessclub42/\
index.html
[root@CentOS65 ~]# echo 'HaCkInG iS fUn At HuNtEr2' > /var/www/html/hunter2/ind\
ex.html
1.5.6. enabling extra websites
The only way to enable or disable configurations in RHEL/CentOS is by renaming or
moving the configuration files. Any file in /etc/httpd/conf.d ending on .conf will be loaded
by Apache. To disable a site we can either rename the file or move it to another directory.
The files are created, so we can tell apache.
[root@CentOS65 ~]# ls /etc/httpd/conf.d/
chessclub42.conf choochoo.conf hunter2.conf README welcome.conf
[root@CentOS65 ~]# service httpd reload
Reloading httpd:
19
apache web server
1.5.7. testing the three websites
Testing the model train club named Choo Choo on port 7000.
[root@CentOS65 ~]# wget 127.0.0.1:7000
--2014-05-11 11:59:36-- http://127.0.0.1:7000/
Connecting to 127.0.0.1:7000... connected.
HTTP request sent, awaiting response... 200 OK
Length: 32 [text/html]
Saving to: `index.html'
100%[===========================================>] 32 --.-K/s in 0s
2014-05-11 11:59:36 (4.47 MB/s) - `index.html' saved [32/32]
[root@CentOS65 ~]# cat index.html
Choo Choo model train Choo Choo
Testing the chess club named Chess Club 42 on port 8000.
[root@CentOS65 ~]# wget 127.0.0.1:8000
--2014-05-11 12:01:30-- http://127.0.0.1:8000/
Connecting to 127.0.0.1:8000... connected.
HTTP request sent, awaiting response... 200 OK
Length: 25 [text/html]
Saving to: `index.html.1'
100%[===========================================>] 25 --.-K/s in 0s
2014-05-11 12:01:30 (4.25 MB/s) - `index.html.1' saved [25/25]
root@debian7:/etc/apache2# cat index.html.1
Welcome to chess club 42
Testing the hacker club named hunter2 on port 9000.
[root@CentOS65 ~]# wget 127.0.0.1:9000
--2014-05-11 12:02:37-- http://127.0.0.1:9000/
Connecting to 127.0.0.1:9000... connected.
HTTP request sent, awaiting response... 200 OK
Length: 26 [text/html]
Saving to: `index.html.2'
100%[===========================================>] 26 --.-K/s in 0s
2014-05-11 12:02:37 (4.49 MB/s) - `index.html.2' saved [26/26]
root@debian7:/etc/apache2# cat index.html.2
HaCkInG iS fUn At HuNtEr2
Cleaning up the temporary files.
[root@CentOS65 ~]# rm index.html index.html.1 index.html.2
20
apache web server
1.5.8. firewall rules
If we attempt to access the site from another machine however, we will not be able to view the
website yet. The firewall is blocking incoming connections. We need to open these incoming
ports first
[root@CentOS65 ~]# iptables -I INPUT -p tcp --dport 80 -j ACCEPT
[root@CentOS65 ~]# iptables -I INPUT -p tcp --dport 7000 -j ACCEPT
[root@CentOS65 ~]# iptables -I INPUT -p tcp --dport 8000 -j ACCEPT
[root@CentOS65 ~]# iptables -I INPUT -p tcp --dport 9000 -j ACCEPT
And if we want these rules to remain active after a reboot, we need to save them
[root@CentOS65 ~]# service iptables save
iptables: Saving firewall rules to /etc/sysconfig/iptables:[ OK ]
21
apache web server
1.6. named virtual hosts on CentOS
1.6.1. named virtual hosts
The chess club and the model train club find the port numbers too hard to remember. They
would prefere to have their website accessible by name.
We continue work on the same server that has three websites on three ports. We need to
make sure those websites are accesible using the names choochoo.local, chessclub42.local
and hunter2.local.
First, we need to enable named virtual hosts in the configuration
[root@CentOS65 ~]# vi /etc/httpd/conf/httpd.conf
[root@CentOS65 ~]# grep ^NameVirtualHost /etc/httpd/conf/httpd.conf
NameVirtualHost *:80
[root@CentOS65 ~]#
Next we need to create three new virtualhosts.
[root@CentOS65 ~]# vi /etc/httpd/conf.d/choochoo.local.conf
[root@CentOS65 ~]# vi /etc/httpd/conf.d/chessclub42.local.conf
[root@CentOS65 ~]# vi /etc/httpd/conf.d/hunter2.local.conf
[root@CentOS65 ~]# cat /etc/httpd/conf.d/choochoo.local.conf
<VirtualHost *:80>
ServerAdmin webmaster@localhost
ServerName choochoo.local
DocumentRoot /var/www/html/choochoo
</VirtualHost>
[root@CentOS65 ~]# cat /etc/httpd/conf.d/chessclub42.local.conf
<VirtualHost *:80>
ServerAdmin webmaster@localhost
ServerName chessclub42.local
DocumentRoot /var/www/html/chessclub42
</VirtualHost>
[root@CentOS65 ~]# cat /etc/httpd/conf.d/hunter2.local.conf
<VirtualHost *:80>
ServerAdmin webmaster@localhost
ServerName hunter2.local
DocumentRoot /var/www/html/hunter2
</VirtualHost>
[root@CentOS65 ~]#
Notice that they all listen on port 80 and have an extra ServerName directive.
1.6.2. name resolution
We need some way to resolve names. This can be done with DNS, which is discussed in
another chapter. For this demo it is also possible to quickly add the three names to the /etc/
hosts file.
[root@CentOS65 ~]# grep ^192 /etc/hosts
192.168.1.225 choochoo.local
192.168.1.225 chessclub42.local
192.168.1.225 hunter2.local
Note that you may have another ip address...
22
apache web server
1.6.3. reload and verify
After a service httpd reload the websites should be available by name.
[root@CentOS65 ~]# service httpd reload
Reloading httpd:
[root@CentOS65 ~]# wget chessclub42.local
--2014-05-25 16:59:14-- http://chessclub42.local/
Resolving chessclub42.local... 192.168.1.225
Connecting to chessclub42.local|192.168.1.225|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 25 [text/html]
Saving to: âindex.htmlâ
100%[=============================================>] 25 --.-K/s in 0s
2014-05-25 16:59:15 (1014 KB/s) - `index.html' saved [25/25]
[root@CentOS65 ~]# cat index.html
Welcome to chess club 42
23
apache web server
1.7. password protected website on CentOS
You can secure files and directories in your website with a .htaccess file that refers to a
.htpasswd file. The htpasswd command can create a .htpasswd file that contains a userid
and an (encrypted) password.
This screenshot creates a user and password for the hacker named cliff and uses the -c flag
to create the .htpasswd file.
[root@CentOS65 ~]# htpasswd -c /var/www/.htpasswd cliff
New password:
Re-type new password:
Adding password for user cliff
[root@CentOS65 ~]# cat /var/www/.htpasswd
cliff:QNwTrymMLBctU
Hacker rob also wants access, this screenshot shows how to add a second user and password
to .htpasswd.
[root@CentOS65 ~]# htpasswd /var/www/.htpasswd rob
New password:
Re-type new password:
Adding password for user rob
[root@CentOS65 ~]# cat /var/www/.htpasswd
cliff:QNwTrymMLBctU
rob:EC2vOCcrMXDoM
[root@CentOS65 ~]#
Both Cliff and Rob chose the same password (hunter2), but that is not visible in the
.htpasswd file because of the different salts.
Next we need to create a .htaccess file in the DocumentRoot of the website we want to
protect. This screenshot shows an example.
[root@CentOS65 ~]# cat /var/www/html/hunter2/.htaccess
AuthUserFile /var/www/.htpasswd
AuthName "Members only!"
AuthType Basic
require valid-user
Note that we are protecting the website on port 9000 that we created earlier.
And because we put the website for the Hackerspace named hunter2 in a subdirectory of the
default website, we will need to adjust the AllowOvveride parameter in /etc/httpd/conf/
httpd.conf under the <Directory "/var/www/html"> directive as this screenshot shows.
24
apache web server
[root@CentOS65 ~]# vi /etc/httpd/conf/httpd.conf
<Directory "/var/www/html">
#
# Possible values for the Options directive are "None", "All",
# or any combination of:
# Indexes Includes FollowSymLinks SymLinksifOwnerMatch ExecCGI MultiViews
#
# Note that "MultiViews" must be named *explicitly* --- "Options All"
# doesn't give it to you.
#
# The Options directive is both complicated and important. Please see
# http://httpd.apache.org/docs/2.2/mod/core.html#options
# for more information.
#
Options Indexes FollowSymLinks
#
# AllowOverride controls what directives may be placed in .htaccess files.
# It can be "All", "None", or any combination of the keywords:
# Options FileInfo AuthConfig Limit
#
AllowOverride Authconfig
#
# Controls who can get stuff from this server.
#
Order allow,deny
Allow from all
</Directory>
Now restart the apache2 server and test that it works!
25
apache web server
1.8. troubleshooting apache
When apache restarts, it will verify the syntax of files in the configuration folder /etc/
apache2 on debian or /etc/httpd on CentOS and it will tell you the name of the faulty file,
the line number and an explanation of the error.
root@debian7:~# service apache2 restart
apache2: Syntax error on line 268 of /etc/apache2/apache2.conf: Syntax error o\
n line 1 of /etc/apache2/sites-enabled/chessclub42: /etc/apache2/sites-enabled\
/chessclub42:4: <VirtualHost> was not closed.\n/etc/apache2/sites-enabled/ches\
sclub42:1: <VirtualHost> was not closed.
Action 'configtest' failed.
The Apache error log may have more information.
failed!
Below you see the problem... a missing / before on line 4.
root@debian7:~# cat /etc/apache2/sites-available/chessclub42
<VirtualHost *:8000>
ServerAdmin webmaster@localhost
DocumentRoot /var/www/chessclub42
<VirtualHost>
Let us force another error by renaming the directory of one of our websites:
root@debian7:~# mv /var/www/choochoo/ /var/www/chooshoo
root@debian7:~# !ser
service apache2 restart
Restarting web server: apache2Warning: DocumentRoot [/var/www/choochoo] does n\
ot exist
Warning: DocumentRoot [/var/www/choochoo] does not exist
... waiting Warning: DocumentRoot [/var/www/choochoo] does not exist
Warning: DocumentRoot [/var/www/choochoo] does not exist
.
As you can see, apache will tell you exactly what is wrong.
You can also troubleshoot by connecting to the website via a browser and then checking the
apache log files in /var/log/apache.
26
apache web server
1.9. virtual hosts example
Below is a sample virtual host configuration. This virtual hosts overrules the default Apache
ErrorDocument directive.
<VirtualHost 83.217.76.245:80>
ServerName cobbaut.be
ServerAlias www.cobbaut.be
DocumentRoot /home/paul/public_html
ErrorLog /home/paul/logs/error_log
CustomLog /home/paul/logs/access_log common
ScriptAlias /cgi-bin/ /home/paul/cgi-bin/
<Directory /home/paul/public_html>
Options Indexes IncludesNOEXEC FollowSymLinks
allow from all
</Directory>
ErrorDocument 404 http://www.cobbaut.be/cobbaut.php
</VirtualHost>
1.10. aliases and redirects
Apache supports aliases for directories, like this example shows.
Alias /paul/ "/home/paul/public_html/"
Similarly, content can be redirected to another website or web server.
Redirect permanent /foo http://www.foo.com/bar
1.11. more on .htaccess
You can do much more with .htaccess. One example is to use .htaccess to prevent people
from certain domains to access your website. Like in this case, where a number of referer
spammers are blocked from the website.
paul@lounge:~/cobbaut.be$ cat .htaccess
# Options +FollowSymlinks
RewriteEngine On
RewriteCond %{HTTP_REFERER} ^http://(www\.)?buy-adipex.fw.nu.*$ [OR]
RewriteCond %{HTTP_REFERER} ^http://(www\.)?buy-levitra.asso.ws.*$ [NC,OR]
RewriteCond %{HTTP_REFERER} ^http://(www\.)?buy-tramadol.fw.nu.*$ [NC,OR]
RewriteCond %{HTTP_REFERER} ^http://(www\.)?buy-viagra.lookin.at.*$ [NC,OR]
...
RewriteCond %{HTTP_REFERER} ^http://(www\.)?www.healthinsurancehelp.net.*$ [NC]
RewriteRule .* - [F,L]
paul@lounge:~/cobbaut.be$
1.12. traffic
Apache keeps a log of all visitors. The webalizer is often used to parse this log into nice
html statistics.
27
apache web server
1.13. self signed cert on Debian
Below is a very quick guide on setting up Apache2 on Debian 7 with a self-signed certificate.
Chances are these packages are already installed.
root@debian7:~# aptitude install apache2 openssl
No packages will be installed, upgraded, or removed.
0 packages upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
Need to get 0 B of archives. After unpacking 0 B will be used.
Create a directory to store the certs, and use openssl to create a self signed cert that is valid
for 999 days.
root@debian7:~# mkdir /etc/ssl/localcerts
root@debian7:~# openssl req -new -x509 -days 999 -nodes -out /etc/ssl/local\
certs/apache.pem -keyout /etc/ssl/localcerts/apache.key
Generating a 2048 bit RSA private key
...
...
writing new private key to '/etc/ssl/localcerts/apache.key'
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [AU]:BE
State or Province Name (full name) [Some-State]:Antwerp
Locality Name (eg, city) []:Antwerp
Organization Name (eg, company) [Internet Widgits Pty Ltd]:linux-training.be
Organizational Unit Name (eg, section) []:
Common Name (e.g. server FQDN or YOUR name) []:Paul
Email Address []:
A little security never hurt anyone.
root@debian7:~# ls -l /etc/ssl/localcerts/
total 8
-rw-r--r-- 1 root root 1704 Sep 16 18:24 apache.key
-rw-r--r-- 1 root root 1302 Sep 16 18:24 apache.pem
root@debian7:~# chmod 600 /etc/ssl/localcerts/*
root@debian7:~# ls -l /etc/ssl/localcerts/
total 8
-rw------- 1 root root 1704 Sep 16 18:24 apache.key
-rw------- 1 root root 1302 Sep 16 18:24 apache.pem
Enable the apache ssl mod.
root@debian7:~# a2enmod ssl
Enabling module ssl.
See /usr/share/doc/apache2.2-common/README.Debian.gz on how to configure SSL\
and create self-signed certificates.
To activate the new configuration, you need to run:
service apache2 restart
Create the website configuration.
root@debian7:~# vi /etc/apache2/sites-available/choochoos
28
apache web server
root@debian7:~# cat /etc/apache2/sites-available/choochoos
<VirtualHost *:7000>
ServerAdmin webmaster@localhost
DocumentRoot /var/www/choochoos
SSLEngine On
SSLCertificateFile /etc/ssl/localcerts/apache.pem
SSLCertificateKeyFile /etc/ssl/localcerts/apache.key
</VirtualHost>
root@debian7:~#
And create the website itself.
root@debian7:/var/www/choochoos# vi index.html
root@debian7:/var/www/choochoos# cat index.html
Choo Choo HTTPS secured model train Choo Choo
Enable the website and restart (or reload) apache2.
root@debian7:/var/www/choochoos# a2ensite choochoos
Enabling site choochoos.
To activate the new configuration, you need to run:
service apache2 reload
root@debian7:/var/www/choochoos# service apache2 restart
Restarting web server: apache2 ... waiting .
Chances are your browser will warn you about the self signed certificate.
29
apache web server
1.14. self signed cert on RHEL/CentOS
Below is a quick way to create a self signed cert for https on RHEL/CentOS. You may need
these packages:
[root@paulserver ~]# yum install httpd openssl mod_ssl
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base: ftp.belnet.be
* extras: ftp.belnet.be
* updates: mirrors.vooservers.com
base | 3.7 kB 00:00
Setting up Install Process
Package httpd-2.2.15-31.el6.centos.x86_64 already installed and latest version
Package openssl-1.0.1e-16.el6_5.15.x86_64 already installed and latest version
Package 1:mod_ssl-2.2.15-31.el6.centos.x86_64 already ins... and latest version
Nothing to do
We use openssl to create the certificate.
[root@paulserver ~]# mkdir certs
[root@paulserver ~]# cd certs
[root@paulserver certs]# openssl genrsa -out ca.key 2048
Generating RSA private key, 2048 bit long modulus
.........+++
.........................................................+++
e is 65537 (0x10001)
[root@paulserver certs]# openssl req -new -key ca.key -out ca.csr
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [XX]:BE
State or Province Name (full name) []:antwerp
Locality Name (eg, city) [Default City]:antwerp
Organization Name (eg, company) [Default Company Ltd]:antwerp
Organizational Unit Name (eg, section) []:
Common Name (eg, your name or your server's hostname) []:paulserver
Email Address []:
Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:
[root@paulserver certs]# openssl x509 -req -days 365 -in ca.csr -signkey ca.ke\
y -out ca.crt
Signature ok
subject=/C=BE/ST=antwerp/L=antwerp/O=antwerp/CN=paulserver
Getting Private key
We copy the keys to the right location (You may be missing SELinux info here).
[root@paulserver certs]# cp ca.crt /etc/pki/tls/certs/
[root@paulserver certs]# cp ca.key ca.csr /etc/pki/tls/private/
We add the location of our keys to this file, and also add the NameVirtualHost *:443
directive.
[root@paulserver certs]# vi /etc/httpd/conf.d/ssl.conf
30
apache web server
[root@paulserver certs]# grep ^SSLCerti /etc/httpd/conf.d/ssl.conf
SSLCertificateFile /etc/pki/tls/certs/ca.crt
SSLCertificateKeyFile /etc/pki/tls/private/ca.key
Create a website configuration.
[root@paulserver certs]# vi /etc/httpd/conf.d/choochoos.conf
[root@paulserver certs]# cat /etc/httpd/conf.d/choochoos.conf
<VirtualHost *:443>
SSLEngine on
SSLCertificateFile /etc/pki/tls/certs/ca.crt
SSLCertificateKeyFile /etc/pki/tls/private/ca.key
DocumentRoot /var/www/choochoos
ServerName paulserver
</VirtualHost>
[root@paulserver certs]#
Create a simple website and restart apache.
[root@paulserver certs]# mkdir /var/www/choochoos
[root@paulserver certs]# echo HTTPS model train choochoos > /var/www/choochoos/\
index.html
[root@paulserver httpd]# service httpd restart
Stopping httpd: [ OK ]
Starting httpd: [ OK ]
And your browser will probably warn you that this certificate is self signed.
31
apache web server
1.15. practice: apache
1. Verify that Apache is installed and running.
2. Browse to the Apache HTML manual.
3. Create three virtual hosts that listen on ports 8472, 31337 and 1201. Test that it all works.
4. Create three named virtual hosts startrek.local, starwars.local and stargate.local. Test that
it all works.
5. Create a virtual hosts that listens on another ip-address.
6. Protect one of your websites with a user/password combo.
32
Chapter 2. introduction to squid
2.1. about proxy servers
2.1.1. usage
A proxy server is a server that caches the internet. Clients connect to the proxy server with
a request for an internet server. The proxy server will connect to the internet server on behalf
of the client. The proxy server will also cache the pages retrieved from the internet server.
A proxy server may provide pages from his cache to a client, instead of connecting to the
internet server to retrieve the (same) pages.
A proxy server has two main advantages. It improves web surfing speed when returning
cached data to clients, and it reduces the required bandwidth (cost) to the internet.
Smaller organizations sometimes put the proxy server on the same physical computer that
serves as a NAT to the internet. In larger organizations, the proxy server is one of many
servers in the DMZ.
When web traffic passes via a proxy server, it is common practice to configure the proxy
with extra settings for access control. Access control in a proxy server can mean user account
access, but also website(url), ip-address or dns restrictions.
2.1.2. open proxy servers
You can find lists of open proxy servers on the internet that enable you to surf anonymously.
This works when the proxy server connects on your behalf to a website, without logging
your ip-address. But be careful, these (listed) open proxy servers could be created in order
to eavesdrop upon their users.
2.1.3. squid
This module is an introduction to the squid proxy server (http://www.squid-cache.org). We
will first configure squid as a normal proxy server.
33
introduction to squid
2.2. installing squid
This screenshot shows how to install squid on Debian with aptitude. Use yum if you are
on Red Hat/CentOS.
root@debian7:~# aptitude install squid
The following NEW packages will be installed:
squid squid-common{a} squid-langpack{a}
0 packages upgraded, 3 newly installed, 0 to remove and 0 not upgraded.
Need to get 1,513 kB of archives. After unpacking 4,540 kB will be used.
Do you want to continue? [Y/n/?]
...output truncated...
Setting up squid-langpack (20120616-1) ...
Setting up squid-common (2.7.STABLE9-4.1) ...
Setting up squid (2.7.STABLE9-4.1) ...
Creating squid spool directory structure
2014/08/01 15:19:31| Creating Swap Directories
Restarting Squid HTTP proxy: squid.
squid's main configuration file is /etc/squid/squid.conf. The file explains every parameter
in great detail.
root@debian7:~# wc -l /etc/squid/squid.conf
4948 /etc/squid/squid.conf
2.3. port 3128
By default the squid proxy server will lsiten to port 3128.
root@debian7:~# grep ^http_port /etc/squid/squid.conf
http_port 3128
root@debian7:~#
2.4. starting and stopping
You can manage squid with the standard service command as shown in this screenshot.
root@debian7:~# service squid start
Starting Squid HTTP proxy: squid.
root@debian7:~# service squid restart
Restarting Squid HTTP proxy: squid.
root@debian7:~# service squid status
squid is running.
root@debian7:~# service squid stop
Stopping Squid HTTP proxy: squid.
root@debian7:~#
34
introduction to squid
2.5. client proxy settings
To enable a proxy server in Firefox or Iceweasel go to Edit Preferences and configure as
shown in this screenshot (replace 192.168.1.60 with the ip address of your proxy server).
Test that your internet works with the proxy enabled. Also test that after a service squid
stop command on your proxy server that you get a message similar to this schreenshot.
35
introduction to squid
To enable a proxy server with Google Chrome (or Debian Chromium) start the program
from the command line like this:
paul@debian7:~$ chromium --proxy-server='192.168.1.60:3128'
Disabling the proxy with service squid stop should result in an error message similar to
this screenshot.
36
introduction to squid
2.6. upside down images
A proxy server sits inbetween your browser and the internet. So besides caching of internet
data (the original function of a proxy server) and besides firewall like restrictions based on
www content, a proxy server is in the perfect position to alter the webpages that you visit.
You could for instance change the advertising on a webpage (or remove certain advertisers),
or like we do in this example; change all images so they are upside down.
The server needs command line tools to manipulate images and a perl script that uses these
tools (and wget to download the images locally and serve them with apache2). In this
example we use imagemagick (which provides tools like convert and mogrify).
root@debian7:~# aptitude install imagemagick wget perl apache2
...output truncated...
root@debian7:~# dpkg -S $(readlink -f $(which mogrify))
imagemagick: /usr/bin/mogrify.im6
root@debian7:~#
The perl script that is shown in the screenshot below can be found on several websites, yet
I have not found the original author. It is however a very simple script that uses wget and
mogrify to download images (.jpg .gif and .png), flip them and store them in /var/www/
images.
root@debian7:~# cat /usr/local/bin/flip.pl
#!/usr/bin/perl
$|=1;
$count = 0;
$pid = $$;
while (<>) {
chomp $_;
if ($_ =~ /(.*\.jpg)/i) {
$url = $1;
system("/usr/bin/wget", "-q", "-O","/var/www/images/$pid-$count.jpg", "$url");
system("/usr/bin/mogrify", "-flip","/var/www/images/$pid-$count.jpg");
print "http://127.0.0.1/images/$pid-$count.jpg\n";
}
elsif ($_ =~ /(.*\.gif)/i) {
$url = $1;
system("/usr/bin/wget", "-q", "-O","/var/www/images/$pid-$count.gif", "$url");
system("/usr/bin/mogrify", "-flip","/var/www/images/$pid-$count.gif");
print "http://127.0.0.1/images/$pid-$count.gif\n";
}
elsif ($_ =~ /(.*\.png)/i) {
$url = $1;
system("/usr/bin/wget", "-q", "-O","/var/www/images/$pid-$count.png", "$url");
system("/usr/bin/mogrify", "-flip","/var/www/images/$pid-$count.png");
print "http://127.0.0.1/images/$pid-$count.png\n";
}
else {
print "$_\n";;
}
$count++;
}
Change (or enable) also the following line in /etc/squid/suiqd.conf.
http_access allow localnet
http_port 3128 transparent
37
introduction to squid
url_rwwrite_program /usr/local/bin/flip.pl
The directory this script uses is /var/www/images and should be accessible by both the
squid server (which uses the user named proxy and by the apache2 webserver (which
uses the user www-data. The screenshot below shows how to create this directory, set the
permissions and make the users a member of the other groups.
root@debian7:~# mkdir /var/www/images
root@debian7:~# chown www-data:www-data /var/www/images
root@debian7:~# chmod 755 /var/www/images
root@debian7:~# usermod -aG www-data proxy
root@debian7:~# usermod -aG proxy www-data
Test that it works after restarting squid and apache2.
38
introduction to squid
2.7. /var/log/squid
The standard log file location for squid is /var/log/squid.
[root@RHEL4 ~]# grep "/var/log" /etc/squid/squid.conf
# cache_access_log /var/log/squid/access.log
# cache_log /var/log/squid/cache.log
# cache_store_log /var/log/squid/store.log
2.8. access control
The default squid setup only allows localhost access. To enable access for a private network
range, look for the "INSERT YOUR OWN RULE(S) HERE..." sentence in squid.conf and
add two lines similar to the screenshot below.
# INSERT YOUR OWN RULE(S) HERE TO ALLOW ACCESS FROM YOUR CLIENTS
acl company_network src 192.168.1.0/24
http_access allow company_network
2.9. testing squid
First, make sure that the server running squid has access to the internet.
[root@RHEL4 ~]# wget -q http://linux-training.be/index.html
[root@RHEL4 ~]# ls -l index.html
-rw-r--r-- 1 root root 2269 Sep 18 13:18 index.html
[root@RHEL4 ~]#
Then configure a browser on a client to use the proxy server, or you could set the
HTTP_PROXY (sometimes http_proxy) variable to point command line programs to the
proxy.
[root@fedora ~]# export HTTP_PROXY=http://192.168.1.39:8080
[root@ubuntu ~]# export http_proxy=http://192.168.1.39:8080
Testing a client machine can then be done with wget (wget -q is used to simplify the
screenshot).
[root@RHEL5 ~]# > /etc/resolv.conf
[root@RHEL5 ~]# wget -q http://www.linux-training.be/index.html
[root@RHEL5 ~]# ls -l index.html
-rw-r--r-- 1 root root 2269 Sep 18 2008 index.html
[root@RHEL5 ~]#
2.10. name resolution
You need name resolution working on the squid server, but you don't need name resolution
on the clients.
[paul@RHEL5 ~]$ wget http://grep.be
--14:35:44-- http://grep.be
Resolving grep.be... failed: Temporary failure in name resolution.
[paul@RHEL5 ~]$ export http_proxy=http://192.168.1.39:8080
[paul@RHEL5 ~]$ wget http://grep.be
--14:35:49-- http://grep.be/
39
introduction to squid
Connecting to 192.168.1.39:8080... connected.
Proxy request sent, awaiting response... 200 OK
Length: 5390 (5.3K) [text/html]
Saving to: `index.html.1'
100%[================================>] 5,390 --.-K/s in 0.1s
14:38:29 (54.8 KB/s) - `index.html' saved [5390/5390]
[paul@RHEL5 ~]$
40
Part II. mysql database
Table of Contents
3. introduction to sql using mysql ............................................................................................................. 43
3.1. installing mysql ............................................................................................................................. 44
3.2. accessing mysql ............................................................................................................................. 45
3.3. mysql databases ............................................................................................................................. 47
3.4. mysql tables .................................................................................................................................. 49
3.5. mysql records ................................................................................................................................ 51
3.6. joining two tables .......................................................................................................................... 54
3.7. mysql triggers ................................................................................................................................ 55
42
Chapter 3. 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.
43
introduction to sql using mysql
3.1. 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.
44
introduction to sql using mysql
3.2. accessing mysql
3.2.1. 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
3.2.2. 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.
...
45
introduction to sql using mysql
3.2.3. ~/.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)
3.2.4. 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.
46
introduction to sql using mysql
3.3. mysql databases
3.3.1. 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)
3.3.2. 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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introduction to sql using mysql
3.3.3. 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>
3.3.4. 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)
3.3.5. 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)
3.3.6. 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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introduction to sql using mysql
3.4. mysql tables
3.4.1. 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)
3.4.2. 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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introduction to sql using mysql
3.4.3. 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)
3.4.4. 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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introduction to sql using mysql
3.5. mysql records
3.5.1. 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'
3.5.2. 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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introduction to sql using mysql
3.5.3. 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)
3.5.4. 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)
3.5.5. 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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introduction to sql using mysql
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)
3.5.6. 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)
3.5.7. 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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introduction to sql using mysql
| 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)
3.5.8. 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)
3.6. joining two tables
3.6.1. 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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introduction to sql using mysql
| 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.
3.6.2. 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.
3.7. mysql triggers
3.7.1. 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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introduction to sql using mysql
-> 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)
3.7.2. 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 III. dns server
Table of Contents
4. introduction to DNS ................................................................................................................................ 59
4.1. about dns ....................................................................................................................................... 60
4.2. dns namespace .............................................................................................................................. 63
4.3. caching only servers ..................................................................................................................... 68
4.4. authoritative dns servers ............................................................................................................... 71
4.5. primary and secondary .................................................................................................................. 71
4.6. zone transfers ................................................................................................................................ 71
4.7. master and slave ............................................................................................................................ 73
4.8. SOA record ................................................................................................................................... 73
4.9. full or incremental zone transfers ................................................................................................. 74
4.10. DNS cache .................................................................................................................................. 75
4.11. forward lookup zone example .................................................................................................... 76
4.12. example: caching only DNS server ............................................................................................ 77
4.13. example: caching only with forwarder ....................................................................................... 79
4.14. example: primary authoritative server ........................................................................................ 81
4.15. example: a DNS slave server ..................................................................................................... 85
4.16. practice: dns ................................................................................................................................ 87
4.17. solution: dns ................................................................................................................................ 88
5. advanced DNS .......................................................................................................................................... 89
5.1. example: DNS round robin ........................................................................................................... 90
5.2. DNS delegation ............................................................................................................................. 91
5.3. example: DNS delegation ............................................................................................................. 92
5.4. example: split-horizon dns ............................................................................................................ 94
5.5. old dns topics ................................................................................................................................ 96
58
Chapter 4. introduction to DNS
dns is a fundamental part of every large computer network. dns is used by many network
services to translate names into network addresses and to locate services on the network
(by name).
Whenever you visit a web site, send an e-mail, log on to Active Directory, play Minecraft,
chat, or use VoIP, there will be one or (many) more queries to dns services.
Should dns fail at your organization, then the whole network will grind to a halt (unless you
hardcoded the network addresses).
You will notice that even the largest of organizations benefit greatly from having one dns
infrastructure. Thus dns requires all business units to work together.
Even at home, most home modems and routers have builtin dns functionality.
This module will explain what dns actually is and how to set it up using Linux and bind9.
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introduction to DNS
4.1. about dns
4.1.1. name to ip address resolution
The domain name system or dns is a service on a tcp/ip network that enables clients to
translate names into ip addresses. Actually dns is much more than that, but let's keep it
simple for now.
When you use a browser to go to a website, then you type the name of that website in the
url bar. But for your computer to actually communicate with the web server hosting said
website, your computer needs the ip address of that web server. That is where dns comes in.
In wireshark you can use the dns filter to see this traffic.
4.1.2. history
In the Seventies, only a few hundred computers were connected to the internet. To resolve
names, computers had a flat file that contained a table to resolve hostnames to ip addresses.
This local file was downloaded from hosts.txt on an ftp server in Stanford.
In 1984 Paul Mockapetris created dns, a distributed treelike hierarchical database that will
be explained in detail in these chapters.
Today, dns or domain name system is a worldwide distributed hierarchical database
controlled by ICANN. Its primary function is to resolve names to ip addresses, and to point
to internet servers providing smtp or ldap services.
The old hosts.txt file is still active today on most computer systems under the name /etc/
hosts (or C:/Windows/System32/Drivers/etc/hosts). We will discuss this file later, as it can
influence name resolution.
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introduction to DNS
4.1.3. forward and reverse lookup queries
The question a client asks a dns server is called a query. When a client queries for an ip
address, this is called a forward lookup query (as seen in the previous drawing).
The reverse, a query for the name of a host, is called a reverse lookup query.
Below a picture of a reverse lookup query.
Here is a screenshot of a reverse lookup query in nslookup.
root@debian7:~# nslookup
> set type=PTR
> 188.93.155.87
Server: 192.168.1.42
Address: 192.168.1.42#53
Non-authoritative answer:
87.155.93.188.in-addr.arpa name = antares.ginsys.net.
This is what a reverse lookup looks like when sniffing with tcpdump.
root@debian7:~# tcpdump udp port 53
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
11:01:29.357685 IP 192.168.1.103.42041 > 192.168.1.42.domain: 14763+ PT\
R? 87.155.93.188.in-addr.arpa. (44)
11:01:29.640093 IP 192.168.1.42.domain > 192.168.1.103.42041: 14763 1/0\
/0 PTR antares.ginsys.net. (76)
And here is what it looks like in wireshark (note this is an older screenshot).
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introduction to DNS
4.1.4. /etc/resolv.conf
A client computer needs to know the ip address of the dns server to be able to send queries
to it. This is either provided by a dhcp server or manually entered.
Linux clients keep this information in the /etc/resolv.conf file.
root@debian7:~# cat /etc/resolv.conf
domain linux-training.be
search linux-training.be
nameserver 192.168.1.42
root@debian7:~#
You can manually change the ip address in this file to use another dns server. For example
Google provides a public name server at 8.8.8.8 and 8.8.4.4.
root@debian7:~# cat /etc/resolv.conf
nameserver 8.8.8.8
root@debian7:~#
Please note that on dhcp clients this value can be overwritten when the dhcp lease is
renewed.
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introduction to DNS
4.2. dns namespace
4.2.1. hierarchy
The dns namespace is hierarchical tree structure, with the root servers (aka dot-servers) at
the top. The root servers are usually represented by a dot.
Below the root-servers are the Top Level Domains or tld's.
There are more tld's than shown in the picture. Currently about 200 countries have a tld. And
there are several general tld's like .com, .edu, .org, .gov, .net, .mil, .int and more recently
also .aero, .info, .museum, ...
4.2.2. root servers
There are thirteen root servers on the internet, they are named A to M. Journalists often
refer to these servers as the master servers of the internet, because if these servers go
down, then nobody can (use names to) connect to websites.
The root servers are not thirteen physical machines, they are many more. For example the
F root server consists of 46 physical machines that all behave as one (using anycast).
http://root-servers.org
http://f.root-servers.org
http://en.wikipedia.org/wiki/Root_nameserver.
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introduction to DNS
4.2.3. root hints
Every dns server software will come with a list of root hints to locate the root servers.
This screenshot shows a small portion of the root hints file that comes with bind 9.8.4.
root@debian7:~# grep -w 'A ' /etc/bind/db.root
A.ROOT-SERVERS.NET. 3600000 A 198.41.0.4
B.ROOT-SERVERS.NET. 3600000 A 192.228.79.201
C.ROOT-SERVERS.NET. 3600000 A 192.33.4.12
D.ROOT-SERVERS.NET. 3600000 A 199.7.91.13
E.ROOT-SERVERS.NET. 3600000 A 192.203.230.10
F.ROOT-SERVERS.NET. 3600000 A 192.5.5.241
G.ROOT-SERVERS.NET. 3600000 A 192.112.36.4
H.ROOT-SERVERS.NET. 3600000 A 128.63.2.53
I.ROOT-SERVERS.NET. 3600000 A 192.36.148.17
J.ROOT-SERVERS.NET. 3600000 A 192.58.128.30
K.ROOT-SERVERS.NET. 3600000 A 193.0.14.129
L.ROOT-SERVERS.NET. 3600000 A 199.7.83.42
M.ROOT-SERVERS.NET. 3600000 A 202.12.27.33
root@debian7:~#
4.2.4. domains
One level below the top level domains are the domains. Domains can have subdomains
(also called child domains).
This picture shows dns domains like google.com, chess.com, linux-training.be (there are
millions more).
DNS domains are registered at the tld servers, the tld servers are registered at the dot
servers.
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introduction to DNS
4.2.5. top level domains
Below the root level are the top level domains or tld's. Originally there were only seven
defined:
Table 4.1. the first top level domains
year TLD purpose
1985 .arpa Reverse lookup via in-addr.arpa
1985 .com Commercial Organizations
1985 .edu US Educational Institutions
1985 .gov US Government Institutions
1985 .mil US Military
1985 .net Internet Service Providers, Internet Infrastructure
1985 .org Non profit Organizations
1988 .int International Treaties like nato.int
Country tld's were defined for individual countries, like .uk in 1985 for Great Britain (yes
really), .be for Belgium in 1988 and .fr for France in 1986. See RFC 1591 for more info.
In 1998 seven new general purpose tld's where chosen, they became active in the 21st
century.
Table 4.2. new general purpose tld's
year TLD purpose
2002 .aero aviation related
2001 .biz businesses
2001 .coop for co-operatives
2001 .info informative internet resources
2001 .museum for museums
2001 .name for all kinds of names, pseudonyms and labels...
2004 .pro for professionals
Many people were surprised by the choices, claiming not much use for them and wanting
a separate .xxx domain (introduced in 2011) for adult content, and .kidz a save haven for
children. In the meantime more useless tld's were create like .travel (for travel agents) and
.tel (for internet communications) and .jobs (for jobs sites).
In 2012 ICANN released a list of 2000 new tld's that would gradually become available.
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introduction to DNS
4.2.6. fully qualified domain name
The fully qualified domain name or fqdn is the combination of the hostname of a machine
appended with its domain name.
If for example a system is called gwen and it is in the domain linux-training.be, then the
fqdn of this system is gwen.linux-training.be.
On Linux systems you can use the hostname and dnsdomainname commands to verify
this information.
root@gwen:~# hostname
gwen
root@gwen:~# dnsdomainname
linux-training.be
root@gwen:~# hostname --fqdn
gwen.linux-training.be
root@gwen:~# cat /etc/debian_version
6.0.10
4.2.7. dns zones
A zone (aka a zone of authority) is a portion of the DNS tree that covers one domain name
or child domain name. The picture below represents zones as blue ovals. Some zones will
contain delegate authority over a child domain to another zone.
A dns server can be authoritative over 0, 1 or more dns zones. We will see more details
later on the relation between a dns server and a dns zone.
A dns zone consists of records, also called resource records. We will list some of those
resource records on the next page.
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introduction to DNS
4.2.8. dns records
A record
The A record, which is also called a host record contains the ipv4-address of a computer.
When a DNS client queries a DNS server for an A record, then the DNS server will resolve
the hostname in the query to an ip address. An AAAA record is similar but contains an ipv6
address instead of ipv4.
PTR record
A PTR record is the reverse of an A record. It contains the name of a computer and can be
used to resolve an ip address to a hostname.
NS record
A NS record or nameserver record is a record that points to a DNS name server (in this
zone). You can list all your name servers for your DNS zone in distinct NS records.
glue A record
An A record that maps the name of an NS record to an ip address is said to be a glue record.
SOA record
The SOA record of a zone contains meta information about the zone itself. The contents of
the SOA record is explained in detail in the section about zone transfers. There is exactly
one SOA record for each zone.
CNAME record
A CNAME record maps a hostname to a hostname, creating effectively an alias for an
existing hostname. The name of the mail server is often aliased to mail or smtp, and the
name of a web server to www.
MX record
The MX record points to an smtp server. When you send an email to another domain, then
your mail server will need the MX record of the target domain's mail server.
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introduction to DNS
4.3. caching only servers
A dns server that is set up without authority over a zone, but that is connected to other
name servers and caches the queries is called a caching only name server. Caching only
name servers do not have a zone database with resource records. Instead they connect to
other name servers and cache that information.
There are two kinds of caching only name servers. Those with a forwarder, and those that
use the root servers.
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introduction to DNS
4.3.1. caching only server without forwarder
A caching only server without forwarder will have to get information elsewhere. When it
receives a query from a client, then it will consult one of the root servers. The root server
will refer it to a tld server, which will refer it to another dns server. That last server might
know the answer to the query, or may refer to yet another server. In the end, our hard working
dns server will find an answer and report this back to the client.
In the picture below, the clients asks for the ip address of linux-training.be. Our caching only
server will contact the root server, and be refered to the .be server. It will then contact the .be
server and be refered to one of the name servers of Openminds. One of these name servers
(in this cas ns1.openminds.be) will answer the query with the ip address of linux-training.be.
When our caching only server reports this to the client, then the client can connect to this
website.
Sniffing with tcpdump will give you this (the first 20 characters of each line are cut).
192.168.1.103.41251 > M.ROOT-SERVERS.NET.domain: 37279% [1au] A? linux-tr\
aining.be. (46)
M.ROOT-SERVERS.NET.domain > 192.168.1.103.41251: 37279- 0/11/13 (740)
192.168.1.103.65268 > d.ns.dns.be.domain: 38555% [1au] A? linux-training.\
be. (46)
d.ns.dns.be.domain > 192.168.1.103.65268: 38555- 0/7/5 (737)
192.168.1.103.7514 > ns2.openminds.be.domain: 60888% [1au] A? linux-train\
ing.be. (46)
ns2.openminds.be.domain > 192.168.1.103.7514: 60888*- 1/0/1 A 188.93.155.\
87 (62)
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introduction to DNS
4.3.2. caching only server with forwarder
A caching only server with a forwarder is a DNS server that will get all its information
from the forwarder. The forwarder must be a dns server for example the dns server of
an internet service provider.
This picture shows a dns server on the company LAN that has set the dns server from their
isp as a forwarder. If the ip address of the isp dns server is 212.71.8.10, then the following
lines would occur in the named.conf file of the company dns server:
forwarders {
212.71.8.10;
};
You can also configure your dns server to work with conditional forwarder(s). The
definition of a conditional forwarder looks like this.
zone "someotherdomain.local" {
type forward;
forward only;
forwarders { 10.104.42.1; };
};
4.3.3. iterative or recursive query
A recursive query is a DNS query where the client that is submitting the query expects a
complete answer (Like the fat red arrow above going from the Macbook to the DNS server).
An iterative query is a DNS query where the client does not expect a complete answer (the
three black arrows originating from the DNS server in the picture above). Iterative queries
usually take place between name servers. The root name servers do not respond to recursive
queries.
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introduction to DNS
4.4. authoritative dns servers
A DNS server that is controlling a zone, is said to be the authoritative DNS server for that
zone. Remember that a zone is a collection of resource records.
4.5. primary and secondary
When you set up the first authoritative dns server for a zone, then this is called the primary
dns server. This server will have a readable and writable copy of the zone database. For
reasons of fault tolerance, performance or load balancing you may decide to set up another
dns server with authority over that zone. This is called a secondary dns server.
4.6. zone transfers
The slave server receives a copy of the zone database from the master server using a
zone transfer. Zone transfers are requested by the slave servers at regular intervals. Those
intervals are defined in the soa record.
You can force a refresh from a zone with rndc. The example below force a transfer of the
fred.local zone, and shows the log from /var/log/syslog.
root@debian7:/etc/bind# rndc refresh fred.local
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introduction to DNS
root@debian7:/etc/bind# grep fred /var/log/syslog | tail -7 | cut -c38-
zone fred.local/IN: sending notifies (serial 1)
received control channel command 'refresh fred.local'
zone fred.local/IN: Transfer started.
transfer of 'fred.local/IN' from 10.104.109.1#53: connected using 10.104.33.30#57367
zone fred.local/IN: transferred serial 2
transfer of 'fred.local/IN' from 10.104.109.1#53: Transfer completed: 1 messages, 10 records, 2
zone fred.local/IN: sending notifies (serial 2)
root@debian7:/etc/bind#
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introduction to DNS
4.7. master and slave
When adding a secondary dns server to a zone, then you will configure this server as a
slave server to the primary server. The primary server then becomes the master server
of the slave server.
Often the primary dns server is the master server of all slaves. Sometimes a slave server
is master server for a second line slave server. In the picture below ns1 is the primary dns
server and ns2, ns3 and ns4 are secondaries. The master for slaves ns2 and ns3 is ns1, but
the master for ns4 is ns2.
4.8. SOA record
The soa record contains a refresh value. If this is set to 30 minutes, then the slave server
will request a copy of the zone file every 30 minutes. There is also a retry value. The retry
value is used when the master server did not reply to the last zone transfer request. The value
for expiry time says how long the slave server will answer to queries, without receiving
a zone update.
Below an example of how to use nslookup to query the soa record of a zone (linux-
training.be).
root@debian6:~# nslookup
> set type=SOA
> server ns1.openminds.be
> linux-training.be
Server: ns1.openminds.be
Address: 195.47.215.14#53
linux-training.be
origin = ns1.openminds.be
mail addr = hostmaster.openminds.be
serial = 2321001133
refresh = 14400
retry = 3600
expire = 604800
minimum = 3600
Zone transfers only occur when the zone database was updated (meaning when one or more
resource records were added, removed or changed on the master server). The slave server
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introduction to DNS
will compare the serial number of its own copy of the SOA record with the serial number
of its master's SOA record. When both serial numbers are the same, then no update is needed
(because no records were added, removed or deleted). When the slave has a lower serial
number than its master, then a zone transfer is requested.
Below a zone transfer captured in wireshark.
4.9. full or incremental zone transfers
When a zone tranfer occurs, this can be either a full zone transfer or an incremental zone
transfer. The decision depends on the size of the transfer that is needed to completely update
the zone on the slave server. An incremental zone transfer is prefered when the total size
of changes is smaller than the size of the zone database. Full zone transfers use the axfr
protocol, incremental zone transfer use the ixfr protocol.
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introduction to DNS
4.10. DNS cache
DNS is a caching protocol.
When a client queries its local DNS server, and the local DNS server is not authoritative
for the query, then this server will go looking for an authoritative name server in the DNS
tree. The local name server will first query a root server, then a tld server and then a domain
server. When the local name server resolves the query, then it will relay this information to
the client that submitted the query, and it will also keep a copy of these queries in its cache.
So when a(nother) client submits the same query to this name server, then it will retrieve
this information form its cache.
For example, a client queries for the A record on www.linux-training.be to its local server.
This is the first query ever received by this local server. The local server checks that it is
not authoritative for the linux-training.be domain, nor for the .be tld, and it is also not a root
server. So the local server will use the root hints to send an iterative query to a root server.
The root server will reply with a reference to the server that is authoritative for the .be
domain (root DNS servers do not resolve fqdn's, and root servers do not respond to recursive
queries).
The local server will then sent an iterative query to the authoritative server for the .be tld.
This server will respond with a reference to the name server that is authoritative for the
linux-training.be domain.
The local server will then sent the query for www.linux-training.be to the authoritative server
(or one of its slave servers) for the linux-training.be domain. When the local server receives
the ip address for www.linux-training.be, then it will provide this information to the client
that submitted this query.
Besides caching the A record for www.linux-training.be, the local server will also cache the
NS and A record for the linux-training.be name server and the .be name server.
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introduction to DNS
4.11. forward lookup zone example
The way to set up zones in /etc/bind/named.conf.local is to create a zone entry with a
reference to another file (this other file contains the zone database).
Here is an example of such an entry in /etc/bind/named.conf.local:
root@debian7:~# cat /etc/bind/named.conf.local
//
// Do any local configuration here
//
// Consider adding the 1918 zones here, if they are not used in your
// organization
//include "/etc/bind/zones.rfc1918";
zone "paul.local" IN {
type master;
file "/etc/bind/db.paul.local";
allow-update { none; };
};
root@debian7:~#
To create the zone file, the easy method is to copy an existing zone file (this is easier than
writing from scratch).
root@debian7:/etc/bind# cp db.empty db.paul.local
root@debian7:/etc/bind# vi db.paul.local
Here is an example of a zone file.
root@debian7:/etc/bind# cat db.paul.local
; zone for classroom teaching
$TTL 86400
@ IN SOA debianpaul.paul.local. root.paul.local (
2014100100 ; Serial
1h ; Refresh
1h ; Retry
2h ; Expire
86400 ) ; Negative Cache TTL
;
; name servers
;
IN NS ns1
IN NS debianpaul
IN NS debian7
;
; servers
;
debianpaul IN A 10.104.33.30
debian7 IN A 10.104.33.30
ns1 IN A 10.104.33.30
;www IN A 10.104.33.30
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introduction to DNS
4.12. example: caching only DNS server
1. installing DNS software on Debian
root@debian7:~# aptitude update && aptitude upgrade
...
root@debian7:~# aptitude install bind9
...
root@debian7:~# dpkg -l | grep bind9 | tr -s ' '
ii bind9 1:9.8.4.dfsg.P1-6+nmu2+deb7u2 amd64 Internet Domain Name Server
ii bind9-host 1:9.8.4.dfsg.P1-6+nmu2+deb7u2 amd64 Version of 'host' bundled...
ii bind9utils 1:9.8.4.dfsg.P1-6+nmu2+deb7u2 amd64 Utilities for BIND
ii libbind9-80 1:9.8.4.dfsg.P1-6+nmu2+deb7u2 amd64 BIND9 Shared Library use...
root@debian7:~#
2. Discover the default configuration files. Can you define the purpose of each file ?
root@debian7:~# ls -l /etc/bind
total 52
-rw-r--r-- 1 root root 2389 Sep 5 20:25 bind.keys
-rw-r--r-- 1 root root 237 Sep 5 20:25 db.0
-rw-r--r-- 1 root root 271 Sep 5 20:25 db.127
-rw-r--r-- 1 root root 237 Sep 5 20:25 db.255
-rw-r--r-- 1 root root 353 Sep 5 20:25 db.empty
-rw-r--r-- 1 root root 270 Sep 5 20:25 db.local
-rw-r--r-- 1 root root 3048 Sep 5 20:25 db.root
-rw-r--r-- 1 root bind 463 Sep 5 20:25 named.conf
-rw-r--r-- 1 root bind 490 Sep 5 20:25 named.conf.default-zones
-rw-r--r-- 1 root bind 374 Oct 1 20:01 named.conf.local
-rw-r--r-- 1 root bind 913 Oct 1 13:24 named.conf.options
-rw-r----- 1 bind bind 77 Oct 1 11:14 rndc.key
-rw-r--r-- 1 root root 1317 Sep 5 20:25 zones.rfc191
3. Setup caching only dns server. This is normally the default setup. A caching-only name
server will look up names for you and cache them. Many tutorials will tell you to add a
forwarder, but we first try without this!
Hey this seems to work without a forwarder. Using a sniffer you can find out what really
happens. Your freshly install dns server is not using a cache, and it is not using your local
dns server (from /etc/resolv.conf). So where is this information coming from ? And what
can you learn from sniffing this dns traffic ?
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introduction to DNS
4. Explain in detail what happens when you enable a caching only dns server without
forwarder. This wireshark screenshot can help, but you learn more by sniffing the traffic
yourself.
You should see traffic to a root name server whenever you try a new tld for the first time.
Remember that dns is a caching protocol, which means that repeating a query will generate
a lot less traffic since your dns server will still have the answer in its memory.
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introduction to DNS
4.13. example: caching only with forwarder
5. Add the public Google dns server as a forwarder. The ip address of this server is 8.8.8.8 .
Before the change:
root@debian7:~# grep -A2 'forwarders {' /etc/bind/named.conf.options
// forwarders {
// 0.0.0.0;
// };
changing:
root@debian7:~# vi /etc/bind/named.conf.options
After the change:
root@debian7:~# grep -A2 'forwarders {' /etc/bind/named.conf.options
forwarders {
8.8.8.8;
};
Restart the server:
root@debian7:~# service bind9 restart
Stopping domain name service...: bind9.
Starting domain name service...: bind9.
6. Explain the purpose of adding the forwarder. What is our dns server doing when it
receives a query ?
root@debian7:~# nslookup
> server
Default server: 10.104.33.30
Address: 10.104.33.30#53
> linux-training.be
Server: 10.104.33.30
Address: 10.104.33.30#53
Non-authoritative answer:
Name: linux-training.be
Address: 188.93.155.87
>
This is the output of tcpdump udp port 53 while executing the above query for linux-
training.be in nslookup.
root@debian7:~# tcpdump udp port 53
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
You should find the following two lines in the output of tcpdump:
10.104.33.30.19381 > google-public-dns-a.google.com.domain: 18237+% [1au] A? \
linux-training.be. (46)
google-public-dns-a.google.com.domain > 10.104.33.30.19381: 18237 1/0/1 A 188\
.93.155.87 (62)
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introduction to DNS
Below is an (old) wireshark screenshot that can help, you should see something similar (but
with different ip addresses).
7. What happens when you query for the same domain name more than once ?
8. Why does it say "non-authoritative answer" ? When is a dns server authoritative ?
9. You can also use dig instead of nslookup.
root@debian7:~# dig @10.104.33.30 linux-training.be +short
188.93.155.87
root@debian7:~#
10. How can we avoid having to set the server in dig or nslookup ?
Change this:
root@debian7:~# cat /etc/resolv.conf
nameserver 10.46.101.1
root@debian7:~#
into this:
root@debian7:~# cat /etc/resolv.conf
nameserver 10.104.33.30
root@debian7:~#
11. When you use dig for the first time for a domain, where is the answer coming from ?
And the second time ? How can you tell ?
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introduction to DNS
4.14. example: primary authoritative server
1. Instead of only cachng the information from other servers, we will now make our server
authoritative for our own domain.
2. I choose the top level domain .local and the domain paul.local and put the information
in /etc/bind/named.conf.local.
root@debian7:~# cat /etc/bind/named.conf.local
//
// Do any local configuration here
//
// Consider adding the 1918 zones here, if they are not used in your
// organization
//include "/etc/bind/zones.rfc1918";
zone "paul.local" IN {
type master;
file "/etc/bind/db.paul.local";
allow-update { none; };
};
3. Also add a zone database file, similar to this one (add some A records for testing). Set
the Refresh and Retry values not too high so you can sniff this traffic (this example makes
the slave server contact the master every hour).
root@debian7:~# cat /etc/bind/db.paul.local
; zone for classroom teaching
$TTL 86400
@ IN SOA debianpaul.paul.local. root.paul.local (
2014100101 ; Serial
1h ; Refresh
1h ; Retry
2h ; Expire
900 ) ; Negative Cache TTL
;
; name servers
;
IN NS ns1
IN NS debianpaul
IN NS debian7
;
; servers
;
debianpaul IN A 10.104.33.30
debian7 IN A 10.104.33.30
ns1 IN A 10.104.33.30
;www IN A 10.104.33.30
root@debian7:~#
Note that the www record is commented out, so it will not resolve.
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introduction to DNS
4.14.1. using your own DNS server
If you are confident that your dns server works, then set it as default and only dns server
in /etc/resolv.conf.
root@debian7:~# cat /etc/resolv.conf
nameserver 10.104.33.30
root@debian7:~#
In case you also use dhclient, you will need to add your dns server to /etc/dhcp/
dhclient.conf.
root@debian7:~# diff /etc/dhcp/dhclient.conf /etc/dhcp/dhclient.conf.original
21c21
< prepend domain-name-servers 10.104.33.30;
---
> #prepend domain-name-servers 127.0.0.1;
23,24c23
< # domain-name, domain-name-servers, domain-search, host-name,
< domain-name, domain-search, host-name,
---
> domain-name, domain-name-servers, domain-search, host-name,
root@debian7:~#
The above screenshot shows that 10.104.33.30 is now a default option that the dhcp client
should no longer request from the dhcp server.
Adjust /etc/hosts to reflect your domain name and verify with hostname and
dnsdomainname.
root@debian7:~# grep debian7 /etc/hosts
127.0.1.1 debian7.paul.local debian7
root@debian7:~# hostname
debian7
root@debian7:~# hostname --fqdn
debian7.paul.local
root@debian7:~# dnsdomainname
paul.local
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introduction to DNS
4.14.2. using your own domain
Consider the following screenshot:
root@debian7b:~# cat /etc/resolv.conf
nameserver 10.104.33.30
root@debian7b:~# ping -c1 www
ping: unknown host www
root@debian7b:~# vi /etc/resolv.conf
root@debian7b:~# cat /etc/resolv.conf
nameserver 10.104.33.30
domain paul.local
root@debian7b:~# ping -c1 www
PING www.paul.local (10.104.33.31) 56(84) bytes of data.
64 bytes from 10.104.33.31: icmp_req=1 ttl=64 time=0.021 ms
--- www.paul.local ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.021/0.021/0.021/0.000 ms
root@debian7b:~#
Adding the domain paul.local directive to /etc/resolv.conf allows omitting the domain
when using hostnames.
You can accomplish this feature automatically by adjusting dhclient.conf.
root@debian7:~# grep paul.local /etc/dhcp/dhclient.conf
prepend domain-name "paul.local";
prepend domain-search "paul.local";
root@debian7:~#
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introduction to DNS
4. Restart the DNS server and check your zone in the error log.
root@debian7:~# service bind9 restart
Stopping domain name service...: bind9.
Starting domain name service...: bind9.
root@debian7:~# grep paul.local /var/log/syslog
Oct 6 09:22:18 debian7 named[2707]: zone paul.local/IN: loaded seria\
l 2014100101
Oct 6 09:22:18 debian7 named[2707]: zone paul.local/IN: sending noti\
fies (serial 2014100101)
5. Use dig or nslookup (or even ping) to test your A records.
root@debian7:~# ping -c1 ns1.paul.local
PING ns1.paul.local (10.104.33.30) 56(84) bytes of data.
64 bytes from 10.104.33.30: icmp_req=1 ttl=64 time=0.006 ms
--- ns1.paul.local ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.006/0.006/0.006/0.000 ms
root@debian7:~# ping -c1 www.paul.local
ping: unknown host www.paul.local
Note that the www record was commented out, so it should fail.
root@debian7:~# dig debian7.paul.local
; <<>> DiG 9.8.4-rpz2+rl005.12-P1 <<>> debian7.paul.local
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50491
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 3, ADDITIONAL: 2
;; QUESTION SECTION:
;debian7.paul.local. IN A
;; ANSWER SECTION:
debian7.paul.local. 86400 IN A 10.104.33.30
;; AUTHORITY SECTION:
paul.local. 86400 IN NS ns1.paul.local.
paul.local. 86400 IN NS debian7.paul.local.
paul.local. 86400 IN NS debianpaul.paul.local.
;; ADDITIONAL SECTION:
ns1.paul.local. 86400 IN A 10.104.33.30
debianpaul.paul.local. 86400 IN A 10.104.33.30
;; Query time: 4 msec
;; SERVER: 10.104.33.30#53(10.104.33.30)
;; WHEN: Mon Oct 6 09:35:25 2014
;; MSG SIZE rcvd: 141
root@debian7:~#
6. Our primary server appears to be up and running. Note the information here:
server os : Debian 7
ip address : 10.104.33.30
domain name: paul.local
server name: ns1.paul.local
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introduction to DNS
4.15. example: a DNS slave server
1. A slave server transfers zone information over the network from a master server (a slave
can also be a master). A primary server maintains zone records in its local file system. As
an exercise, and to verify the work of all students, set up a slave server of all the master
servers in the classroom.
2. Before configuring the slave server, we may have to allow transfers from our zone to this
server. Remember that this is not very secure since transfers are in clear text and limited to
an ip address. This example follows our demo from above.
Imagine a student named Jesse having completed the setup as shown before, with the domain
name jesse.local and the ip address 10.104.15.20. The goal is to have a slave server of
paul.local on Jesse's computer and a slave zone of jesse.local on my computer.
Below is an example of an allow-transfer statement. Careful, maybe the default allows
transfer to any.
root@debian7:/etc/bind# cat named.conf.local
//
// Do any local configuration here
//
// Consider adding the 1918 zones here, if they are not used in your
// organization
//include "/etc/bind/zones.rfc1918";
zone "paul.local" IN {
type master;
file "/etc/bind/db.paul.local";
allow-update { none; };
allow-transfer { 10.104.15.20; };
};
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introduction to DNS
3. With the configuration below I can make my server a slave for the jesse.local zone.
root@debian7:/etc/bind# tail -6 named.conf.local
zone "jesse.local" IN {
type slave;
file "/var/cache/named/db.jesse.local";
masters { 10.104.15.20; };
};
root@debian7:/etc/bind# mkdir /var/cache/named/
root@debian7:/etc/bind# chown bind:bind /var/cache/named/
root@debian7:/etc/bind# ls -ld /var/cache/named/
drwxr-xr-x 2 bind bind 4096 Oct 1 20:01 /var/cache/named/
Note that we put the slave zones in /var/cache/named and not in /etc/bind.
4. Restarting bind on the slave server should transfer the zone database file. Verify this in /
var/log/syslog. (time and date are truncated from the screenshot, and Jesse did not use the
current date in the serial number...)
root@debian7:/etc/bind# grep jesse /var/log/syslog
named[2731]: zone jesse.local/IN: Transfer started.
named[2731]: transfer of 'jesse.local/IN' from 10.104.15.20#53: connected u\
sing 10.104.33.30#44719
named[2731]: zone jesse.local/IN: transferred serial 20110516
named[2731]: transfer of 'jesse.local/IN' from 10.104.15.20#53: Transfer co\
mpleted: 1 messages, 8 records, 239 bytes, 0.001 secs (239000 bytes/sec)
And the contents of the slave zone:
root@debian7:/etc/bind# cat /var/cache/named/db.jesse.local
$ORIGIN .
$TTL 604800 ; 1 week
jesse.local IN SOA ns.jesse.local. root.jesse.local.jesse.local. (
20110516 ; serial
300 ; refresh (5 minutes)
200 ; retry (3 minutes 20 seconds)
2419200 ; expire (4 weeks)
604800 ; minimum (1 week)
)
NS ns.jesse.local.
$ORIGIN jesse.local.
anya A 10.104.15.1
mac A 10.104.15.30
ns A 10.104.15.20
ubu1010srv A 10.104.15.20
www A 10.104.15.25
root@debian7:/etc/bind#
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introduction to DNS
4.16. practice: dns
1. Install bind9 and verify with a sniffer how it works.
2. Add a forwarder and verify that it works.
3. Create a primary forward lookup zone named yourname.local with at least two NS
records and four A records.
4. Use dig and nslookup to verify your NS and A records.
5. Create a slave of your primary zone (on another server) and verify the zone transfer.
6. Set up two primary zones on two servers and implement a conditional forwarder (you
can use the two servers from before).
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introduction to DNS
4.17. solution: dns
1. Install bind9 and verify with a sniffer how it works.
You should see queries to the root name servers with tcpdump or wireshark.
2. Add a forwarder and verify that it works.
The forwarder van be added in named.conf.options as seen in the theory.
3. Create a primary forward lookup zone named yourname.local with at least two NS
records and four A records.
This is literally explained in the theory.
4. Use dig and nslookup to verify your NS and A records.
This is literally explained in the theory.
5. Create a slave of your primary zone (on another server) and verify the zone transfer.
This is literally explained in the theory.
6. Set up two primary zones on two servers and implement a conditional forwarder (you
can use the two servers from before).
A conditional forwarder is set in named.conf.local as a zone.
(see the theory on forwarder)
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Chapter 5. advanced DNS
This chapter expands your DNS server with topics like round robin dns for load balancing
servers, dns delegation to delegate child domains to another team and split horizon dns so
you can provide local service locations to clients.
There is more to dns, content will be added rsn.
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advanced DNS
5.1. example: DNS round robin
When you create multiple A records for the same name, then bind will do a round robin of
the order in which the records are returned. This allows the use of DNS as a load balancer
between hosts, since clients will usually take the first ip-address offered.
Consider this example from the /etc/bind/db.paul.local zone configuration file. There are
two A records for www pointing to two distinct ip addresses.
root@debian7:~# grep www /etc/bind/db.paul.local
www IN A 10.104.33.30
www IN A 10.104.33.31
Below a screenshot of nslookup querying a load balanced A record. Notice the order of ip
addresses returned.
root@debian7:~# nslookup www.paul.local 10.104.33.30
Server: 10.104.33.30
Address: 10.104.33.30#53
Name: www.paul.local
Address: 10.104.33.31
Name: www.paul.local
Address: 10.104.33.30
root@debian7:~# nslookup www.paul.local 10.104.33.30
Server: 10.104.33.30
Address: 10.104.33.30#53
Name: www.paul.local
Address: 10.104.33.30
Name: www.paul.local
Address: 10.104.33.31
Try to set up a website on two web servers (with a small difference so you can distinguish
the websites) and test the round robin.
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5.2. DNS delegation
You can delegate a child domain to another DNS server. The child domain then becomes
a new zone, with authority at the new dns server.
When delegation is properly set up, then clients that query your parent zone will also be
able to resolve the delegated child zones.
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advanced DNS
5.3. example: DNS delegation
We have another Linux server named debian7b and we want to make it responsible for the
child domain test42.paul.local.
Note the name of the servers in the screenshots are either debian7 (hosting the parent
domain) or debian7b (hosting the child domain).
We start by adjusting the /etc/bind/named.comf.local file (on the server hosting the parent
domain) to make sure that no forwarder will be used when resolving authoritative names.
root@debian7:~# grep -A4 paul.local /etc/bind/named.conf.local
zone "paul.local" IN {
type master;
file "/etc/bind/db.paul.local";
allow-update { none; };
allow-transfer { 10.104.15.20; };
forwarders { };
};
root@debian7:~#
Technically, you could also set allow-transfer to { any; }; while troubleshooting and then
refine it later, but this is not needed for delegation.
Then we add the delegation to our zone database:
root@debian7:~# tail -3 /etc/bind/db.paul.local
$ORIGIN test42.paul.local.
@ IN NS ns2.test42.paul.local.
ns2 IN A 10.104.33.31 ; the glue record
root@debian7:~#
Don't forget to restart bind and verify /var/log/syslog.
root@debian7:~# service bind9 restart
Stopping domain name service...: bind9.
Starting domain name service...: bind9.
root@debian7:~# grep paul.local /var/log/syslog | cut -c28- | tail -2
named[3202]: zone paul.local/IN: loaded serial 2014100801
named[3202]: zone paul.local/IN: sending notifies (serial 2014100801)
root@debian7:~#
Note that on your terminal you can type tail -40 /var/log/syslog because the only reason I
use grep, cut and tail -2 is to limit the size of the screenshots in this book.
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advanced DNS
Next we create a zone database file on the second server, as seen in this screenshot:
root@debian7b:~# cat /etc/bind/db.test42.paul.local
; child zone for classroom teaching
$TTL 86400
$ORIGIN test42.paul.local.
@ IN SOA ns2.test42.paul.local. root.test42.paul.local. (
2014100802 ; Serial
1h ; Refresh
1h ; Retry
2h ; Expire
900 ) ; Negative Cache TTL
;
; name servers
;
IN NS ns2.test42.paul.local.
IN NS debian7b.test42.paul.local.
;
; servers
;
ns2 IN A 10.104.33.31
debian7b IN A 10.104.33.31
testsrv IN A 10.104.33.31
root@debian7b:~#
The second server also needs a zone definition in named.conf.local, followed by a restart
of bind.
root@debian7b:~# cat /etc/bind/named.conf.local
//
// Do any local configuration here
//
// Consider adding the 1918 zones here, if they are not used in your
// organization
//include "/etc/bind/zones.rfc1918";
zone "test42.paul.local" IN {
type master;
file "/etc/bind/db.test42.paul.local";
allow-update { none; };
allow-transfer { any; };
};
root@debian7b:~#
Testing on the parent server:
root@debian7:~# dig ns1.paul.local +short
10.104.33.30
root@debian7:~# dig ns2.test42.paul.local +short
10.104.33.31
root@debian7:~# dig debian7b.test42.paul.local +short
10.104.33.31
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advanced DNS
5.4. example: split-horizon dns
Suppose you want to answer dns queries depending on who is asking. For example
when someone from the 10.104.15.0/24 network (managed by Jesse) asks for the A
record www.paul.local, then dns answers with 10.104.33.30. But when someone from the
10.104.42.0/24 network (managed by Keith) asks for the same A record of www.paul.local,
he will get 10.104.33.31 as an answer.
A split-horizon setup can be used to redirect people to local copies of certain services.
In this example we want to decide on specific answers for two networks (Jesse's and Keith's)
and prevent them from using our dns server for recursion, while maintaining the capability
to resolve the internet and our paul.local zone from our own network.
We start by creating three view clauses in named.conf.local.
root@debian7:/etc/bind# cat named.conf.local
view "paul" {
match-clients { 10.104.33.0; localhost; };
include "/etc/bind/named.conf.default-zones";
zone "paul.local" IN {
type master;
file "/etc/bind/db.paul.local";
allow-update { none; };
};
}; // end view internal
view "jesse" {
match-clients { 10.104.15/24; };
zone "paul.local" IN {
type master;
file "/etc/bind/db.paul.local.jesse";
allow-update { none; };
};
}; // end view jesse
view "keith" {
match-clients { 10.104.42/24; };
zone "paul.local" IN {
type master;
file "/etc/bind/db.paul.local.keith";
allow-update { none; };
};
}; // end view keith
Note that we included the default-zones in the internal zone. It is mandatory to put all zones
inside views when using a view.
The zone files are identical copies, except for the www record. You can see that the
round robin is still active for internal users, computers from 10.104.15.0/24 (Jesse) will
always receive 10.104.33.30 while computers from 10.104.42.0/24 (Keith) will receive
10.104.33.31.
root@debian7:/etc/bind# grep www db.paul.local db.paul.local.[jk]*
db.paul.local:www IN A 10.104.33.30
db.paul.local:www IN A 10.104.33.31
db.paul.local.jesse:www IN A 10.104.33.30
db.paul.local.keith:www IN A 10.104.33.31
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advanced DNS
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advanced DNS
5.5. old dns topics
All the dns things below this paragraph are old and in urgent need of review.
5.5.1. old example: reverse DNS
1. We can add ip to name resolution to our dns-server using a reverse dns zone.
2. Start by adding a .arpa zone to /etc/bind/named.conf.local like this (we set notify to no to
avoid sending of notify messages to other name servers):
root@ubu1010srv:/etc/bind# grep -A4 arpa named.conf.local
zone "1.168.192.in-addr.arpa" {
type master;
notify no;
file "/etc/bind/db.192";
};
3. Also create a zone database file for this reverse lookup zone.
root@ubu1010srv:/etc/bind# cat db.192
;
; BIND reverse data file for 192.168.1.0/24 network
;
$TTL 604800
@ IN SOA ns.cobbaut.paul root.cobbaut.paul. (
20110516 ; Serial
604800 ; Refresh
86400 ; Retry
2419200 ; Expire
604800 ) ; Negative Cache TTL
;
@ IN NS ns.
37 IN PTR ns.cobbaut.paul.
1 IN PTR anya.cobbaut.paul.
30 IN PTR mac.cobbaut.paul.
root@ubu1010srv:/etc/bind#
4. Test with nslookup or dig:
root@ubu1010srv:/etc/bind# dig 1.168.192.in-addr.arpa AXFR
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advanced DNS
5.5.2. old DNS load balancing
Not as above. When you have more than one DNS server authoritative for a zone, you can
spread queries amongst all server. One way to do this is by creating NS records for all servers
that participate in the load balancing of external queries.
You could also configure different name servers on internal clients.
5.5.3. old DNS notify
The original design of DNS in rfc 1034 and rfc 1035 implemented a refresh time in the
SOA record to configure a time loop for slaves to query their master server. This can result
in a lot of useless pull requests, or in a significant lag between updates.
For this reason dns notify (rfc 1996) was designed. The server will now notify slaves
whenever there is an update. By default this feature is activated in bind.
Notify can be disabled as in this screenshot.
zone "1.168.192.in-addr.arpa" {
type master;
notify no;
file "/etc/bind/db.192";
};
5.5.4. old testing IXFR and AXFR
Full zone transfers (AXFR) are initiated when you restart the bind server, or when you
manually update the zone database file directly. With nsupdate you can update a zone
database and initiate an incremental zone transfer.
You need DDNS allowed for nsupdate to work.
root@ubu1010srv:/etc/bind# nsupdate
> server 127.0.0.1
> update add mac14.linux-training.be 86400 A 192.168.1.23
> send
update failed: REFUSED
5.5.5. old DDNS integration with DHCP
Some organizations like to have all their client computers in DNS. This can be cumbersome
to maintain. Luckily rfc 2136 describes integration of DHCP servers with a DNS server.
Whenever DHCP acknowledges a client ip configuration, it can notify DNS with this clients
ip-address and name. This is called dynamic updates or DDNS.
5.5.6. old reverse is forward in-addr.arpa
Reverse lookup is actually iomplemented as a forward lookup in the in-addr.arpa domain.
This domain has 256 child domains (from 0.in-addr.arpa to 255.in-addr.arpa), with each
child domain having again 256 child domains. And this twice more to a structure of over
four billion (2 to the power 32) domains.
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advanced DNS
5.5.7. old ipv6
With rfc 3596 came ipv6 extensions for DNS. There is the AAAA record for ipv6 hosts on
the network, and there is the ip6.int domain for reverse lookup (having 16 child domains
from 0.ip6.int to f.ip6.int, each of those having again 16 child domains...and this 16 times.
5.5.8. old DNS security: file corruption
To mitigate file corruption on the zone files and the bind configuration files protect them
with Unix permissions and take regular backups.
5.5.9. old DNS security: zone transfers
Limit zone transfers to certain ip addresses instead of to any. Nevermind that ip-addresses
can be spoofed, still use this.
5.5.10. old DNS security: zone transfers, ip spoofing
You could setup DNSSEC (which is not the easiest to maintain) and with rfc 2845(tsig?) and
with rfc 2930(tkey, but this is open to brute force), or you could disable all zone transfers
and use a script with ssh to copy them manually.
5.5.11. old DNS security: queries
Allow recursion only from the local network, and iterative queries from outside only when
necessary. This can be configured on master and slave servers.
view "internal" {
match-clients { 192.168.42/24; };
recursion yes;
...
};
view "external" {
match-clients { any; };
recursion no;
...
};
Or allow only queries from the local network.
options {
allow-query { 192.168.42.0/24; localhost; };
};
zone "cobbaut.paul" {
allow-query { any; };
};
Or only allow recursive queries from internal clients.
options {
allow-recursion { 192.168.42.0/24; localhost; };
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advanced DNS
};
5.5.12. old DNS security: chrooted bind
Most Linux distributions allow an easy setup of bind in a chrooted environment.
5.5.13. old DNS security: DNSSEC
DNSSEC uses public/private keys to secure communications, this is described in rfc's 4033,
4034 and 4035.
5.5.14. old DNS security: root
Do not run bind as root. Do not run any application daemon as root.
99
Part IV. dhcp server
Table of Contents
6. introduction to dhcp .............................................................................................................................. 102
6.1. four broadcasts ............................................................................................................................ 103
6.2. picturing dhcp ............................................................................................................................. 104
6.3. installing a dhcp server ............................................................................................................... 105
6.4. dhcp server for RHEL/CentOS ................................................................................................... 105
6.5. client reservations ....................................................................................................................... 106
6.6. example config files .................................................................................................................... 106
6.7. older example config files .......................................................................................................... 107
6.8. advanced dhcp ............................................................................................................................. 109
6.9. Practice: dhcp .............................................................................................................................. 110
101
Chapter 6. introduction to dhcp
Dynamic Host Configuration Protocol (or short dhcp) is a standard tcp/ip protocol that
distributes ip configurations to clients. dhcp is defined in rfc 2131 (before that it was defined
as an update to bootp in rfc 1531/1541.
The alternative to dhcp is manually entering the ip configuration on each client computer.
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introduction to dhcp
6.1. four broadcasts
dhcp works with layer 2 broadcasts. A dhcp client that starts, will send a dhcp discover
on the network. All dhcp servers (that have a lease available) will respond with a dhcp
offer. The client will choose one of those offers and will send a dhcp request containing
the chosen offer. The dhcp server usually responds with a dhcp ack(knowledge).
In wireshark it looks like this.
When this procedure is finished, then the client is allowed to use that ip-configuration until
the end of its lease time.
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introduction to dhcp
6.2. picturing dhcp
Here we have a small network with two dhcp servers named DHCP-SRV1 and DHCP-
SRV2 and two clients (SunWS1 and Mac42). All computers are connected by a hub or switch
(pictured in the middle). All four computers have a cable to the hub (cables not pictured).
1. The client SunWS1 sends a dhcp discover on the network. All computers receive this
broadcast.
2. Both dhcp servers answer with a dhcp offer. DHCP-SRV1 is a dedicated dhcp server
and is faster in sending a dhcp offer than DHCP-SRV2 (who happens to also be a file server).
3. The client chooses the offer from DHCP-SRV1 and sends a dhcp request on the network.
4. DHCP-SRV1 answers with a dhcp ack (short for acknowledge).
All four broadcasts (or five when you count both offers) can be layer 2 ethernet broadcast
to mac address ff:ff:ff:ff:ff:ff and a layer 3 ip broadcast to 255.255.255.255.
The same story can be read in rfc 2131.
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introduction to dhcp
6.3. installing a dhcp server
dhcp server for Debian/Mint
debian5:~# aptitude install dhcp3-server
Reading package lists... Done
Building dependency tree
Reading state information... Done
Reading extended state information
Initializing package states... Done
Reading task descriptions... Done
The following NEW packages will be installed:
dhcp3-server
You get a configuration file with many examples.
debian5:~# ls -l /etc/dhcp3/dhcpd.conf
-rw-r--r-- 1 root root 3551 2011-04-10 21:23 /etc/dhcp3/dhcpd.conf
6.4. dhcp server for RHEL/CentOS
Installing is easy with yum.
[root@rhel71 ~]# yum install dhcp
Loaded plugins: product-id, subscription-manager
Resolving Dependencies
--> Running transaction check
---> Package dhcp.x86_64 12:4.2.5-36.el7 will be installed
--> Finished Dependency Resolution
Dependencies Resolved
================================================================================
Package Arch Version Repository Size
================================================================================
Installing:
dhcp x86_64 12:4.2.5-36.el7 rhel-7-server-rpms 510 k
Transaction Summary
================================================================================
Install 1 Package
Total download size: 510 k
Installed size: 1.4 M
Is this ok [y/d/N]: y
Downloading packages:
dhcp-4.2.5-36.el7.x86_64.rpm | 510 kB 00:01
Running transaction check
Running transaction test
Transaction test succeeded
Running transaction
Installing : 12:dhcp-4.2.5-36.el7.x86_64 1/1
Verifying : 12:dhcp-4.2.5-36.el7.x86_64 1/1
Installed:
dhcp.x86_64 12:4.2.5-36.el7
Complete!
[root@rhel71 ~]#
After installing we get a /etc/dhcp/dhcpd.conf that points us to an example file named
dhcpd.conf.sample.
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introduction to dhcp
[root@rhel71 ~]# cat /etc/dhcp/dhcpd.conf
#
# DHCP Server Configuration file.
# see /usr/share/doc/dhcp*/dhcpd.conf.example
# see dhcpd.conf(5) man page
#
[root@rhel71 ~]#
So we copy the sample and adjust it for our real situation. We name the copy /etc/dhcp/
dhcpd.conf.
[root@rhel71 ~]# cp /usr/share/doc/dhcp-4.2.5/dhcpd.conf.example /etc/dhcp/dhcp\
d.conf
[root@rhel71 ~]# vi /etc/dhcp/dhcpd.conf
[root@rhel71 ~]# cat /etc/dhcp/dhcpd.conf
option domain-name "linux-training.be";
option domain-name-servers 10.42.42.42;
default-lease-time 600;
max-lease-time 7200;
log-facility local7;
subnet 10.42.0.0 netmask 255.255.0.0 {
range 10.42.200.11 10.42.200.120;
option routers 10.42.200.1;
}
[root@rhel71 ~]#
The 'routers' option is valid for the subnet alone, whereas the 'domain-name' option is global
(for all subnets).
Time to start the server. Remember to use systemctl start dhcpd on RHEL7/CentOS7 and
service dhcpd start on previous versions of RHEL/CentOS.
[root@rhel71 ~]# systemctl start dhcpd
[root@rhel71 ~]#
6.5. client reservations
You can reserve an ip configuration for a client using the mac address.
host pc42 {
hardware ethernet 11:22:33:44:55:66;
fixed-address 192.168.42.42;
}
You can add individual options to this reservation.
host pc42 {
hardware ethernet 11:22:33:44:55:66;
fixed-address 192.168.42.42;
option domain-name "linux-training.be";
option routers 192.168.42.1;
}
6.6. example config files
Below you see several sections of /etc/dhcp/dhcpd.conf on a Debian 6 server.
# NetSec Antwerp Network
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introduction to dhcp
subnet 192.168.1.0 netmask 255.255.255.0 {
range 192.168.1.20 192.168.1.199;
option domain-name-servers ns1.netsec.local;
option domain-name "netsec.local";
option routers 192.168.1.1;
option broadcast-address 192.168.1.255;
default-lease-time 7200;
max-lease-time 7200;
}
Above the general configuration for the network, with a pool of 180 addresses.
Below two client reservations:
#
# laptops
#
host mac {
hardware ethernet 00:26:bb:xx:xx:xx;
fixed-address mac.netsec.local;
}
host vmac {
hardware ethernet 8c:7b:9d:xx:xx:xx;
fixed-address vmac.netsec.local;
}
6.7. older example config files
For dhcpd.conf on Fedora with dynamic updates for a DNS domain.
[root@fedora14 ~]# cat /etc/dhcp/dhcpd.conf
authoritative;
include "/etc/rndc.key";
log-facility local6;
server-identifier fedora14;
ddns-domainname "office.linux-training.be";
ddns-update-style interim;
ddns-updates on;
update-static-leases on;
option domain-name "office.linux-training.be";
option domain-name-servers 192.168.42.100;
option ip-forwarding off;
default-lease-time 1800;
max-lease-time 3600;
zone office.linux-training.be {
primary 192.168.42.100;
}
subnet 192.168.4.0 netmask 255.255.255.0 {
range 192.168.4.24 192.168.4.40;
}
Allowing any updates in the zone database (part of the named.conf configuration)
zone "office.linux-training.be" {
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introduction to dhcp
type master;
file "/var/named/db.office.linux-training.be";
allow-transfer { any; };
allow-update { any; };
};
Allowing secure key updates in the zone database (part of the named.conf configuration)
zone "office.linux-training.be" {
type master;
file "/var/named/db.office.linux-training.be";
allow-transfer { any; };
allow-update { key mykey; };
};
Sample key file contents:
[root@fedora14 ~]# cat /etc/rndc.key
key "rndc-key" {
algorithm hmac-md5;
secret "4Ykd58uIeUr3Ve6ad1qTfQ==";
};
Generate your own keys with dnssec-keygen.
How to include a key in a config file:
include "/etc/bind/rndc.key";
Also make sure that bind can write to your db.zone file (using chmod/chown). For Ubuntu
this can be in /etc/bind, for Fedora in /var/named.
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introduction to dhcp
6.8. advanced dhcp
6.8.1. 80/20 rule
DHCP servers should not be a single point of failure. Let us discuss redundant dhcp server
setups.
6.8.2. relay agent
To avoid having to place a dhcp server on every segment, we can use dhcp relay agents.
6.8.3. rogue dhcp servers
Rogue dhcp servers are a problem without a solution. For example accidental connection of
a (believed to be simple) hub/switch to a network with an internal dhcp server.
6.8.4. dhcp and ddns
DHCP can dynamically update DNS when it configures a client computer. DDNS can be
used with or without secure keys.
When set up properly records can be added automaticall to the zone file:
root@fedora14~# tail -2 /var/named/db.office.linux-training.be
ubu1010srv A 192.168.42.151
TXT "00dfbb15e144a273c3cf2d6ae933885782"
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introduction to dhcp
6.9. Practice: dhcp
1. Make sure you have a unique fixed ip address for your DNS and DHCP server (easier
on the same machine).
2. Install DHCP and browse the explanation in the default configuration file /etc/dhcp/
dhcpd.conf or /etc/dhcp3/dhcpd.conf.
3. Decide on a valid scope and activate it.
4. Test with a client that your DHCP server works.
5. Use wireshark to capture the four broadcasts when a client receives an ip (for the first
time).
6. Use wireshark to capture a DHCPNAK and a DHCPrelease.
7. Reserve a configuration for a particular client (using mac address).
8. Configure your DHCP/DNS server(s) with a proper hostname and domainname (/etc/
hosts, /etc/hostname, /etc/sysconfig/network on Fedora/RHEL, /etc/resolv.conf ...). You
may need to disable NetworkManager on *buntu-desktops.
9. Make sure your DNS server still works, and is master over (at least) one domain.
There are several ways to do steps 10-11-12. Google is your friend in exploring DDNS with
keys, with key-files or without keys.
10. Configure your DNS server to allow dynamic updates from your DHCP server.
11. Configure your DHCP server to send dynamic updates to your DNS server.
12. Test the working of Dynamic DNS.
110
Part V. iptables firewall
Table of Contents
7. introduction to routers .......................................................................................................................... 113
7.1. router or firewall ......................................................................................................................... 114
7.2. packet forwarding ....................................................................................................................... 114
7.3. packet filtering ............................................................................................................................ 114
7.4. stateful ......................................................................................................................................... 114
7.5. nat (network address translation) ................................................................................................ 115
7.6. pat (port address translation) ...................................................................................................... 115
7.7. snat (source nat) .......................................................................................................................... 115
7.8. masquerading ............................................................................................................................... 115
7.9. dnat (destination nat) .................................................................................................................. 115
7.10. port forwarding ......................................................................................................................... 115
7.11. /proc/sys/net/ipv4/ip_forward .................................................................................................... 116
7.12. /etc/sysctl.conf ........................................................................................................................... 116
7.13. sysctl .......................................................................................................................................... 116
7.14. practice: packet forwarding ...................................................................................................... 117
7.15. solution: packet forwarding ...................................................................................................... 119
8. iptables firewall ...................................................................................................................................... 122
8.1. iptables tables .............................................................................................................................. 123
8.2. starting and stopping iptables ..................................................................................................... 123
8.3. the filter table .............................................................................................................................. 124
8.4. practice: packet filtering ............................................................................................................. 129
8.5. solution: packet filtering ............................................................................................................. 130
8.6. network address translation ........................................................................................................ 131
112
Chapter 7. introduction to routers
What follows is a very brief introduction to using Linux as a router.
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introduction to routers
7.1. router or firewall
A router is a device that connects two networks. A firewall is a device that besides acting
as a router, also contains (and implements) rules to determine whether packets are allowed
to travel from one network to another. A firewall can be configured to block access based
on networks, hosts, protocols and ports. Firewalls can also change the contents of packets
while forwarding them.
7.2. packet forwarding
Packet forwarding means allowing packets to go from one network to another. When a
multihomed host is connected to two different networks, and it allows packets to travel from
one network to another through its two network interfaces, it is said to have enabled packet
forwarding.
7.3. packet filtering
Packet filtering is very similar to packet forwarding, but every packet is individually tested
against rules that decide on allowing or dropping the packet. The rules are stored by iptables.
7.4. stateful
A stateful firewall is an advancement over stateless firewalls that inspect every individual
packet. A stateful firewall will keep a table of active connections, and is knowledgeable
enough to recognise when new connections are part of an active session. Linux iptables is
a stateful firewall.
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introduction to routers
7.5. nat (network address translation)
A nat device is a router that is also changing the source and/or target ip-address in packets.
It is typically used to connect multiple computers in a private address range (rfc 1918) with
the (public) internet. A nat can hide private addresses from the internet.
It is important to understand that people and vendors do not always use the right term when
referring to a certain type of nat. Be sure you talk about the same thing. We can distuinguish
several types of nat.
7.6. pat (port address translation)
nat often includes pat. A pat device is a router that is also changing the source and/or target
tcp/udp port in packets. pat is Cisco terminology and is used by snat, dnat, masquerading
and port forwarding in Linux. RFC 3022 calls it NAPT and defines the nat/pat combo as
"traditional nat". A device sold to you as a nat-device will probably do nat and pat.
7.7. snat (source nat)
A snat device is changing the source ip-address when a packet passes our nat. snat
configuration with iptables includes a fixed target source address.
7.8. masquerading
Masquerading is a form of snat that will hide the (private) source ip-addresses of your
private network using a public ip-address. Masquerading is common on dynamic internet
interfaces (broadband modem/routers). Masquerade configuration with iptables uses a
dynamic target source address.
7.9. dnat (destination nat)
A dnat device is changing the destination ip-address when a packet passes our nat.
7.10. port forwarding
When static dnat is set up in a way that allows outside connections to enter our private
network, then we call it port forwarding.
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7.11. /proc/sys/net/ipv4/ip_forward
Whether a host is forwarding packets is defined in /proc/sys/net/ipv4/ip_forward. The
following screenshot shows how to enable packet forwarding on Linux.
root@router~# echo 1 > /proc/sys/net/ipv4/ip_forward
The next command shows how to disable packet forwarding.
root@router~# echo 0 > /proc/sys/net/ipv4/ip_forward
Use cat to check if packet forwarding is enabled.
root@router~# cat /proc/sys/net/ipv4/ip_forward
7.12. /etc/sysctl.conf
By default, most Linux computers are not configured for automatic packet forwarding.
To enable packet forwarding whenever the system starts, change the net.ipv4.ip_forward
variable in /etc/sysctl.conf to the value 1.
root@router~# grep ip_forward /etc/sysctl.conf
net.ipv4.ip_forward = 0
7.13. sysctl
For more information, take a look at the man page of sysctl.
root@debian6~# man sysctl
root@debian6~# sysctl -a 2>/dev/null | grep ip_forward
net.ipv4.ip_forward = 0
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7.14. practice: packet forwarding
0. You have the option to select (or create) an internal network when adding a network card
in VirtualBox or VMWare. Use this option to create two internal networks. I named them
leftnet and rightnet, but you can choose any other name.
1. Set up two Linux machines, one on leftnet, the other on rightnet. Make sure they both
get an ip-address in the correct subnet. These two machines will be 'left' and 'right' from
the 'router'.
2. Set up a third Linux computer with three network cards, one on leftnet, the other on
rightnet. This computer will be the 'router'. Complete the table below with the relevant
names, ip-addresses and mac-addresses.
Table 7.1. Packet Forwarding Exercise
leftnet computer the router rightnet computer
MAC
IP
3. How can you verify whether the router will allow packet forwarding by default or not ?
Test that you can ping from the router to the two other machines, and from those two
machines to the router. Use arp -a to make sure you are connected with the correct mac
addresses.
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4. Ping from the leftnet computer to the rightnet computer. Enable and/or disable packet
forwarding on the router and verify what happens to the ping between the two networks. If
you do not succeed in pinging between the two networks (on different subnets), then use a
sniffer like wireshark or tcpdump to discover the problem.
5. Use wireshark or tcpdump -xx to answer the following questions. Does the source MAC
change when a packet passes through the filter ? And the destination MAC ? What about
source and destination IP-addresses ?
6. Remember the third network card on the router ? Connect this card to a LAN with internet
connection. On many LAN's the command dhclient eth0 just works (replace eth0 with the
correct interface).
root@router~# dhclient eth0
You now have a setup similar to this picture. What needs to be done to give internet access
to leftnet and rightnet.
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7.15. solution: packet forwarding
1. Set up two Linux machines, one on leftnet, the other on rightnet. Make sure they both
get an ip-address in the correct subnet. These two machines will be 'left' and 'right' from
the 'router'.
The ip configuration on your computers should be similar to the following two screenshots.
Both machines must be in a different subnet (here 192.168.60.0/24 and 192.168.70.0/24). I
created a little script on both machines to configure the interfaces.
root@left~# cat leftnet.sh
pkill dhclient
ifconfig eth0 192.168.60.8 netmask 255.255.255.0
root@right~# cat rightnet.sh
pkill dhclient
ifconfig eth0 192.168.70.9 netmask 255.255.255.0
2. Set up a third Linux computer with three network cards, one on leftnet, the other on
rightnet. This computer will be the 'router'. Complete the table below with the relevant
names, ip-addresses and mac-addresses.
root@router~# cat router.sh
ifconfig eth1 192.168.60.1 netmask 255.255.255.0
ifconfig eth2 192.168.70.1 netmask 255.255.255.0
#echo 1 > /proc/sys/net/ipv4/ip_forward
Your setup may use different ip and mac addresses than the ones in the table below.
Table 7.2. Packet Forwarding Solution
leftnet computer the router rightnet computer
08:00:27:f6:ab:b9 08:00:27:43:1f:5a 08:00:27:be:4a:6b 08:00:27:14:8b:17
192.168.60.8 192.168.60.1 192.168.70.1 192.168.70.9
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3. How can you verify whether the router will allow packet forwarding by default or not ?
Test that you can ping from the router to the two other machines, and from those two
machines to the router. Use arp -a to make sure you are connected with the correct mac
addresses.
This can be done with "grep ip_forward /etc/sysctl.conf" (1 is enabled, 0 is disabled) or
with sysctl -a | grep ip_for.
root@router~# grep ip_for /etc/sysctl.conf
net.ipv4.ip_forward = 0
4. Ping from the leftnet computer to the rightnet computer. Enable and/or disable packet
forwarding on the router and verify what happens to the ping between the two networks. If
you do not succeed in pinging between the two networks (on different subnets), then use a
sniffer like wireshark or tcpdump to discover the problem.
Did you forget to add a default gateway to the LAN machines ? Use route add default
gw 'ip-address'.
root@left~# route add default gw 192.168.60.1
root@right~# route add default gw 192.168.70.1
You should be able to ping when packet forwarding is enabled (and both default gateways
are properly configured). The ping will not work when packet forwarding is disabled or
when gateways are not configured correctly.
5. Use wireshark or tcpdump -xx to answer the following questions. Does the source MAC
change when a packet passes through the filter ? And the destination MAC ? What about
source and destination IP-addresses ?
Both MAC addresses are changed when passing the router. Use tcpdump -xx like this:
root@router~# tcpdump -xx -i eth1
root@router~# tcpdump -xx -i eth2
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6. Remember the third network card on the router ? Connect this card to a LAN with internet
connection. On many LAN's the command dhclient eth0 just works (replace eth0 with the
correct interface.
root@router~# dhclient eth0
You now have a setup similar to this picture. What needs to be done to give internet access
to leftnet and rightnet.
The clients on leftnet and rightnet need a working dns server. We use one of Google's
dns servers here.
echo nameserver 8.8.8.8 > /etc/resolv.conf
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Chapter 8. iptables firewall
This chapter introduces some simple firewall rules and how to configure them with iptables.
iptables is an application that allows a user to configure the firewall functionality built into
the Linux kernel.
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8.1. iptables tables
By default there are three tables in the kernel that contain sets of rules.
The filter table is used for packet filtering.
root@debian6~# iptables -t filter -L
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
The nat table is used for address translation.
root@debian6~# iptables -t nat -L
Chain PREROUTING (policy ACCEPT)
target prot opt source destination
Chain POSTROUTING (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
The mangle table can be used for special-purpose processing of packets.
Series of rules in each table are called a chain. We will discuss chains and the nat table
later in this chapter.
8.2. starting and stopping iptables
The following screenshot shows how to stop and start iptables on Red Hat/Fedora/CentOS
and compatible distributions.
[root@centos6 ~]# service iptables stop
[root@centos6 ~]# service iptables start
iptables: Applying firewall rules [ ok ]
[root@centos6 ~]#
Debian and *buntu distributions do not have this script, but allow for an uninstall.
root@debian6~# aptitude purge iptables
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8.3. the filter table
8.3.1. about packet filtering
Packet filtering is a bit more than packet forwarding. While packet forwarding uses only
a routing table to make decisions, packet filtering also uses a list of rules. The kernel will
inspect packets and decide based on these rules what to do with each packet.
8.3.2. filter table
The filter table in iptables has three chains (sets of rules). The INPUT chain is used for any
packet coming into the system. The OUTPUT chain is for any packet leaving the system.
And the FORWARD chain is for packets that are forwarded (routed) through the system.
The screenshot below shows how to list the filter table and all its rules.
[root@RHEL5 ~]# iptables -t filter -nL
Chain INPUT (policy ACCEPT)
target prot opt source destination
Chain FORWARD (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
[root@RHEL5 ~]#
As you can see, all three chains in the filter table are set to ACCEPT everything. ACCEPT
is the default behaviour.
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8.3.3. setting default rules
The default for the default rule is indeed to ACCEPT everything. This is not the most secure
firewall.
A more secure setup would be to DROP everything. A package that is dropped will not
continue in any chain, and no warning or error will be sent anywhere.
The below commands lock down a computer. Do not execute these commands inside a
remote ssh shell.
root@debianpaul~# iptables -P INPUT DROP
root@debianpaul~# iptables -P OUTPUT DROP
root@debianpaul~# iptables -P FORWARD DROP
root@debianpaul~# iptables -L
Chain INPUT (policy DROP)
target prot opt source destination
Chain FORWARD (policy DROP)
target prot opt source destination
Chain OUTPUT (policy DROP)
target prot opt source destination
8.3.4. changing policy rules
To start, let's set the default policy for all three chains to drop everything. Note that you
might lose your connection when typing this over ssh ;-).
[root@RHEL5 ~]# iptables -P INPUT DROP
[root@RHEL5 ~]# iptables -P FORWARD DROP
[root@RHEL5 ~]# iptables -P OUTPUT DROP
Next, we allow the server to use its own loopback device (this allows the server to access
its services running on localhost). We first append a rule to the INPUT chain to allow
(ACCEPT) traffic from the lo (loopback) interface, then we do the same to allow packets to
leave the system through the loopback interface.
[root@RHEL5 ~]# iptables -A INPUT -i lo -j ACCEPT
[root@RHEL5 ~]# iptables -A OUTPUT -o lo -j ACCEPT
Looking at the filter table again (omitting -t filter because it is the default table).
[root@RHEL5 ~]# iptables -nL
Chain INPUT (policy DROP)
target prot opt source destination
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
Chain FORWARD (policy DROP)
target prot opt source destination
Chain OUTPUT (policy DROP)
target prot opt source destination
ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
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8.3.5. Allowing ssh over eth0
This example show how to add two rules to allow ssh access to your system from outside.
[root@RHEL5 ~]# iptables -A INPUT -i eth0 -p tcp --dport 22 -j ACCEPT
[root@RHEL5 ~]# iptables -A OUTPUT -o eth0 -p tcp --sport 22 -j ACCEPT
The filter table will look something like this screenshot (note that -v is added for more
verbose output).
[root@RHEL5 ~]# iptables -nvL
Chain INPUT (policy DROP 7 packets, 609 bytes)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all -- lo * 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT tcp -- eth0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:22
Chain FORWARD (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy DROP 3 packets, 228 bytes)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all -- * lo 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT tcp -- * eth0 0.0.0.0/0 0.0.0.0/0 tcp spt:22
[root@RHEL5 ~]#
8.3.6. Allowing access from a subnet
This example shows how to allow access from any computer in the 10.1.1.0/24 network, but
only through eth1. There is no port (application) limitation here.
[root@RHEL5 ~]# iptables -A INPUT -i eth1 -s 10.1.1.0/24 -p tcp -j ACCEPT
[root@RHEL5 ~]# iptables -A OUTPUT -o eth1 -d 10.1.1.0/24 -p tcp -j ACCEPT
Together with the previous examples, the policy is expanding.
[root@RHEL5 ~]# iptables -nvL
Chain INPUT (policy DROP 7 packets, 609 bytes)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all -- lo * 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT tcp -- eth0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:22
0 0 ACCEPT tcp -- eth1 * 10.1.1.0/24 0.0.0.0/0
Chain FORWARD (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy DROP 3 packets, 228 bytes)
pkts bytes target prot opt in out source destination
0 0 ACCEPT all -- * lo 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT tcp -- * eth0 0.0.0.0/0 0.0.0.0/0 tcp spt:22
0 0 ACCEPT tcp -- * eth1 0.0.0.0/0 10.1.1.0/24
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8.3.7. iptables save
Use iptables save to automatically implement these rules when the firewall is (re)started.
[root@RHEL5 ~]# /etc/init.d/iptables save
Saving firewall rules to /etc/sysconfig/iptables: [ OK ]
[root@RHEL5 ~]#
8.3.8. scripting example
You can write a simple script for these rules. Below is an example script that implements
the firewall rules that you saw before in this chapter.
#!/bin/bash
# first cleanup everything
iptables -t filter -F
iptables -t filter -X
iptables -t nat -F
iptables -t nat -X
# default drop
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT DROP
# allow loopback device
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT
# allow ssh over eth0 from outside to system
iptables -A INPUT -i eth0 -p tcp --dport 22 -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 22 -j ACCEPT
# allow any traffic from 10.1.1.0/24 to system
iptables -A INPUT -i eth1 -s 10.1.1.0/24 -p tcp -j ACCEPT
iptables -A OUTPUT -o eth1 -d 10.1.1.0/24 -p tcp -j ACCEPT
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8.3.9. Allowing ICMP(ping)
When you enable iptables, you will get an 'Operation not permitted' message when trying
to ping other hosts.
[root@RHEL5 ~# ping 192.168.187.130
PING 192.168.187.130 (192.168.187.130) 56(84) bytes of data.
ping: sendmsg: Operation not permitted
ping: sendmsg: Operation not permitted
The screenshot below shows you how to setup iptables to allow a ping from or to your
machine.
[root@RHEL5 ~]# iptables -A INPUT -p icmp --icmp-type any -j ACCEPT
[root@RHEL5 ~]# iptables -A OUTPUT -p icmp --icmp-type any -j ACCEPT
The previous two lines do not allow other computers to route ping messages through your
router, because it only handles INPUT and OUTPUT. For routing of ping, you will need
to enable it on the FORWARD chain. The following command enables routing of icmp
messages between networks.
[root@RHEL5 ~]# iptables -A FORWARD -p icmp --icmp-type any -j ACCEPT
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iptables firewall
8.4. practice: packet filtering
1. Make sure you can ssh to your router-system when iptables is active.
2. Make sure you can ping to your router-system when iptables is active.
3. Define one of your networks as 'internal' and the other as 'external'. Configure the router
to allow visits to a website (http) to go from the internal network to the external network
(but not in the other direction).
4. Make sure the internal network can ssh to the external, but not the other way around.
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iptables firewall
8.5. solution: packet filtering
A possible solution, where leftnet is the internal and rightnet is the external network.
#!/bin/bash
# first cleanup everything
iptables -t filter -F
iptables -t filter -X
iptables -t nat -F
iptables -t nat -X
# default drop
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT DROP
# allow loopback device
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT
# question 1: allow ssh over eth0
iptables -A INPUT -i eth0 -p tcp --dport 22 -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 22 -j ACCEPT
# question 2: Allow icmp(ping) anywhere
iptables -A INPUT -p icmp --icmp-type any -j ACCEPT
iptables -A FORWARD -p icmp --icmp-type any -j ACCEPT
iptables -A OUTPUT -p icmp --icmp-type any -j ACCEPT
# question 3: allow http from internal(leftnet) to external(rightnet)
iptables -A FORWARD -i eth1 -o eth2 -p tcp --dport 80 -j ACCEPT
iptables -A FORWARD -i eth2 -o eth1 -p tcp --sport 80 -j ACCEPT
# question 4: allow ssh from internal(leftnet) to external(rightnet)
iptables -A FORWARD -i eth1 -o eth2 -p tcp --dport 22 -j ACCEPT
iptables -A FORWARD -i eth2 -o eth1 -p tcp --sport 22 -j ACCEPT
# allow http from external(rightnet) to internal(leftnet)
# iptables -A FORWARD -i eth2 -o eth1 -p tcp --dport 80 -j ACCEPT
# iptables -A FORWARD -i eth1 -o eth2 -p tcp --sport 80 -j ACCEPT
# allow rpcinfo over eth0 from outside to system
# iptables -A INPUT -i eth2 -p tcp --dport 111 -j ACCEPT
# iptables -A OUTPUT -o eth2 -p tcp --sport 111 -j ACCEPT
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8.6. network address translation
8.6.1. about NAT
A NAT device is a router that is also changing the source and/or target ip-address in packets.
It is typically used to connect multiple computers in a private address range with the (public)
internet. A NAT can hide private addresses from the internet.
NAT was developed to mitigate the use of real ip addresses, to allow private address ranges
to reach the internet and back, and to not disclose details about internal networks to the
outside.
The nat table in iptables adds two new chains. PREROUTING allows altering of packets
before they reach the INPUT chain. POSTROUTING allows altering packets after they exit
the OUTPUT chain.
Use iptables -t nat -nvL to look at the NAT table. The screenshot below shows an empty
NAT table.
[root@RHEL5 ~]# iptables -t nat -nL
Chain PREROUTING (policy ACCEPT)
target prot opt source destination
Chain POSTROUTING (policy ACCEPT)
target prot opt source destination
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
[root@RHEL5 ~]#
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8.6.2. SNAT (Source NAT)
The goal of source nat is to change the source address inside a packet before it leaves the
system (e.g. to the internet). The destination will return the packet to the NAT-device. This
means our NAT-device will need to keep a table in memory of all the packets it changed, so
it can deliver the packet to the original source (e.g. in the private network).
Because SNAT is about packets leaving the system, it uses the POSTROUTING chain.
Here is an example SNAT rule. The rule says that packets coming from 10.1.1.0/24 network
and exiting via eth1 will get the source ip-address set to 11.12.13.14. (Note that this is a
one line command!)
iptables -t nat -A POSTROUTING -o eth1 -s 10.1.1.0/24 -j SNAT \
--to-source 11.12.13.14
Of course there must exist a proper iptables filter setup to allow the packet to traverse from
one network to the other.
8.6.3. SNAT example setup
This example script uses a typical nat setup. The internal (eth0) network has access via
SNAT to external (eth1) webservers (port 80).
#!/bin/bash
#
# iptables script for simple classic nat websurfing
# eth0 is internal network, eth1 is internet
#
echo 0 > /proc/sys/net/ipv4/ip_forward
iptables -P INPUT ACCEPT
iptables -P OUTPUT ACCEPT
iptables -P FORWARD DROP
iptables -A FORWARD -i eth0 -o eth1 -s 10.1.1.0/24 -p tcp \
--dport 80 -j ACCEPT
iptables -A FORWARD -i eth1 -o eth0 -d 10.1.1.0/24 -p tcp \
--sport 80 -j ACCEPT
iptables -t nat -A POSTROUTING -o eth1 -s 10.1.1.0/24 -j SNAT \
--to-source 11.12.13.14
echo 1 > /proc/sys/net/ipv4/ip_forward
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8.6.4. IP masquerading
IP masquerading is very similar to SNAT, but is meant for dynamic interfaces. Typical
example are broadband 'router/modems' connected to the internet and receiving a different
ip-address from the isp, each time they are cold-booted.
The only change needed to convert the SNAT script to a masquerading is one line.
iptables -t nat -A POSTROUTING -o eth1 -s 10.1.1.0/24 -j MASQUERADE
8.6.5. DNAT (Destination NAT)
DNAT is typically used to allow packets from the internet to be redirected to an internal
server (in your DMZ) and in a private address range that is inaccessible directly form the
internet.
This example script allows internet users to reach your internal (192.168.1.99) server via
ssh (port 22).
#!/bin/bash
#
# iptables script for DNAT
# eth0 is internal network, eth1 is internet
#
echo 0 > /proc/sys/net/ipv4/ip_forward
iptables -P INPUT ACCEPT
iptables -P OUTPUT ACCEPT
iptables -P FORWARD DROP
iptables -A FORWARD -i eth0 -o eth1 -s 10.1.1.0/24 -j ACCEPT
iptables -A FORWARD -i eth1 -o eth0 -p tcp --dport 22 -j ACCEPT
iptables -t nat -A PREROUTING -i eth1 -p tcp --dport 22 \
-j DNAT --to-destination 10.1.1.99
echo 1 > /proc/sys/net/ipv4/ip_forward
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Part VI. Introduction to Samba
Table of Contents
9. introduction to samba ........................................................................................................................... 137
9.1. verify installed version ............................................................................................................... 138
9.2. installing samba ........................................................................................................................... 139
9.3. documentation ............................................................................................................................. 140
9.4. starting and stopping samba ....................................................................................................... 141
9.5. samba daemons ........................................................................................................................... 142
9.6. the SMB protocol ........................................................................................................................ 143
9.7. practice: introduction to samba .................................................................................................. 144
10. getting started with samba ................................................................................................................. 145
10.1. /etc/samba/smb.conf .................................................................................................................. 146
10.2. /usr/bin/testparm ........................................................................................................................ 147
10.3. /usr/bin/smbclient ....................................................................................................................... 148
10.4. /usr/bin/smbtree ......................................................................................................................... 150
10.5. server string ............................................................................................................................... 151
10.6. Samba Web Administration Tool (SWAT) .............................................................................. 152
10.7. practice: getting started with samba ......................................................................................... 153
10.8. solution: getting started with samba ......................................................................................... 154
11. a read only file server ......................................................................................................................... 156
11.1. Setting up a directory to share ................................................................................................. 157
11.2. configure the share .................................................................................................................... 157
11.3. restart the server ........................................................................................................................ 158
11.4. verify the share ......................................................................................................................... 158
11.5. a note on netcat ......................................................................................................................... 160
11.6. practice: read only file server ................................................................................................... 161
11.7. solution: read only file server ................................................................................................... 162
12. a writable file server ........................................................................................................................... 163
12.1. set up a directory to share ........................................................................................................ 164
12.2. share section in smb.conf ......................................................................................................... 164
12.3. configure the share .................................................................................................................... 164
12.4. test connection with windows .................................................................................................. 164
12.5. test writing with windows ........................................................................................................ 165
12.6. How is this possible ? ............................................................................................................... 165
12.7. practice: writable file server ..................................................................................................... 166
12.8. solution: writable file server ..................................................................................................... 167
13. samba first user account ..................................................................................................................... 168
13.1. creating a samba user ............................................................................................................... 169
13.2. ownership of files ..................................................................................................................... 169
13.3. /usr/bin/smbpasswd .................................................................................................................... 169
13.4. /etc/samba/smbpasswd ............................................................................................................... 169
13.5. passdb backend ......................................................................................................................... 170
13.6. forcing this user ........................................................................................................................ 170
13.7. practice: first samba user account ............................................................................................ 171
13.8. solution: first samba user account ............................................................................................ 172
14. samba authentication .......................................................................................................................... 173
14.1. creating the users on Linux ...................................................................................................... 174
14.2. creating the users on samba ...................................................................................................... 174
14.3. security = user ........................................................................................................................... 174
14.4. configuring the share ................................................................................................................ 175
14.5. testing access with net use ........................................................................................................ 175
14.6. testing access with smbclient .................................................................................................... 175
14.7. verify ownership ....................................................................................................................... 176
14.8. common problems ..................................................................................................................... 176
14.9. practice : samba authentication ................................................................................................. 178
14.10. solution: samba authentication ................................................................................................ 179
15. samba securing shares ........................................................................................................................ 180
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Introduction to Samba
15.1. security based on user name ..................................................................................................... 181
15.2. security based on ip-address ..................................................................................................... 181
15.3. security through obscurity ........................................................................................................ 182
15.4. file system security ................................................................................................................... 182
15.5. practice: securing shares ........................................................................................................... 184
15.6. solution: securing shares ........................................................................................................... 185
16. samba domain member ....................................................................................................................... 187
16.1. changes in smb.conf .................................................................................................................. 188
16.2. joining an Active Directory domain ......................................................................................... 189
16.3. winbind ...................................................................................................................................... 190
16.4. wbinfo ........................................................................................................................................ 190
16.5. getent ......................................................................................................................................... 191
16.6. file ownership ............................................................................................................................ 192
16.7. practice : samba domain member ............................................................................................. 193
17. samba domain controller .................................................................................................................... 194
17.1. about Domain Controllers ......................................................................................................... 195
17.2. About security modes ............................................................................................................... 195
17.3. About password backends ........................................................................................................ 196
17.4. [global] section in smb.conf ..................................................................................................... 196
17.5. netlogon share ........................................................................................................................... 197
17.6. other [share] sections ................................................................................................................ 197
17.7. Users and Groups ...................................................................................................................... 198
17.8. tdbsam ....................................................................................................................................... 198
17.9. about computer accounts .......................................................................................................... 199
17.10. local or roaming profiles ........................................................................................................ 199
17.11. Groups in NTFS acls .............................................................................................................. 200
17.12. logon scripts ............................................................................................................................ 201
17.13. practice: samba domain controller .......................................................................................... 202
18. a brief look at samba 4 ....................................................................................................................... 203
18.1. Samba 4 alpha 6 ....................................................................................................................... 205
136
Chapter 9. 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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9.1. verify installed version
9.1.1. .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
9.1.2. .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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9.2. installing samba
9.2.1. .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
9.2.2. .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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9.3. documentation
9.3.1. 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
...
9.3.2. 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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9.4. 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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9.5. samba daemons
Samba 3 consists of three daemons, they are named nmbd, smbd and winbindd.
9.5.1. 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
9.5.2. 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
9.5.3. 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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9.6. the SMB protocol
9.6.1. 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.
9.6.2. 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.
9.6.3. 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.
9.6.4. 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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9.7. 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 10. getting started with
samba
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getting started with samba
10.1. /etc/samba/smb.conf
10.1.1. 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
10.1.2. 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
10.1.3. 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
10.1.4. 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.
10.1.5. 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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getting started with samba
Kim, Justine, Sabine \
Amelie, Marie, Suzanne
10.1.6. 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.
10.1.7. 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]#
10.2. /usr/bin/testparm
10.2.1. 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
10.2.2. 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.
10.2.3. 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]#
10.3. /usr/bin/smbclient
10.3.1. 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
10.3.2. 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
10.3.3. 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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getting started with samba
IPC$ IPC Remote IPC
ADMIN$ Disk Remote Admin
...
10.4. /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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getting started with samba
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.
10.5. 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
10.6. 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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10.7. 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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10.8. 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 11. a read only file server
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a read only file server
11.1. 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]#
11.2. configure the share
11.2.1. 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.
11.2.2. 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
11.3. 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 ]
11.4. verify the share
11.4.1. 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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11.4.2. 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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11.5. 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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11.6. 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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11.7. 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 12. a writable file server
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12.1. 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/
12.2. 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
12.3. 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
12.4. 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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12.5. 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
12.6. 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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12.7. 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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12.8. 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 13. samba first user account
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samba first user account
13.1. 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.
13.2. 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
13.3. /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.
13.4. /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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samba first user account
sambanobody:503:AE9 ... 9DB309C528E540978:[U ]:LCT-4976B05B:
13.5. 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
13.6. 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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13.7. 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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13.8. 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 14. samba authentication
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samba authentication
14.1. 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.
14.2. 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.
14.3. 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
14.4. 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
14.5. 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.
14.6. 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
14.7. 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
14.8. common problems
14.8.1. 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
14.8.2. 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
14.8.3. 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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14.9. 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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14.10. 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 15. samba securing shares
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samba securing shares
15.1. security based on user name
15.1.1. 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
15.1.2. 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
15.1.3. 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
15.1.4. 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
15.2. security based on ip-address
15.2.1. 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
15.2.2. 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
15.3. security through obscurity
15.3.1. hide unreadable
Setting hide unreadable to yes will prevent users from seeing files that cannot be read by
them.
hide unreadable = yes
15.3.2. 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
15.4. file system security
15.4.1. 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
15.4.2. 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
15.4.3. 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.
15.4.4. 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.
15.4.5. 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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15.5. 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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15.6. 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 16. samba domain member
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16.1. changes in smb.conf
16.1.1. workgroup
The workgroup option in the global section should match the netbios name of the Active
Directory domain.
workgroup = STARGATE
16.1.2. 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
16.1.3. 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
16.1.4. 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
16.1.5. [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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16.1.6. 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
16.1.7. [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
16.2. 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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16.3. winbind
16.3.1. 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
16.3.2. 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]#
16.4. wbinfo
16.4.1. 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
16.4.2. 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
16.4.3. 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
16.4.4. 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
16.5. 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.
16.6. 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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16.7. 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 17. samba domain controller
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17.1. about Domain Controllers
17.1.1. 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.
17.1.2. 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).
17.1.3. 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.
17.1.4. 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!
17.2. About security modes
17.2.1. 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.
17.2.2. 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.
17.2.3. 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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17.2.4. security = ads
This mode will make samba use Kerberos to connect to the Active Directory domain.
17.2.5. security = server
This mode is obsolete, it can be used to forward authentication to another server.
17.3. 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.
17.4. [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.
17.4.1. 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
17.4.2. 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
17.4.3. passdb backend
The passdb backend parameter will determine whether samba uses smbpasswd, tdbsam
or ldap.
passdb backend = tdbsam
17.4.4. preferred master
Setting the preferred master parameter to yes will make the nmbd daemon force an election
on startup.
preferred master = yes
17.4.5. domain logons
Setting the domain logons parameter will make this samba server a domain controller.
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domain logons = yes
17.4.6. 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
17.4.7. [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
17.5. 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
17.6. 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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[football]
comment = Information about football
path = /srv/samba/football
valid users = @ntfootball
read only = No
17.7. 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:
17.8. 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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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.
17.9. 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.
17.10. 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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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
17.11. 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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[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.
17.12. 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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17.13. 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.
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Chapter 18. a brief look at samba 4
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a brief look at samba 4
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a brief look at samba 4
18.1. 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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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
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Part VII. selinux
Table of Contents
19. introduction to SELinux ..................................................................................................................... 209
19.1. selinux modes ............................................................................................................................ 210
19.2. logging ....................................................................................................................................... 210
19.3. activating selinux ...................................................................................................................... 210
19.4. getenforce .................................................................................................................................. 211
19.5. setenforce ................................................................................................................................... 211
19.6. sestatus ....................................................................................................................................... 212
19.7. policy ......................................................................................................................................... 212
19.8. /etc/selinux/config ...................................................................................................................... 212
19.9. DAC or MAC ........................................................................................................................... 213
19.10. ls -Z ......................................................................................................................................... 213
19.11. -Z ............................................................................................................................................. 213
19.12. /selinux ..................................................................................................................................... 214
19.13. identity ..................................................................................................................................... 214
19.14. role ........................................................................................................................................... 214
19.15. type (or domain) ..................................................................................................................... 215
19.16. security context ....................................................................................................................... 216
19.17. transition .................................................................................................................................. 216
19.18. extended attributes .................................................................................................................. 217
19.19. process security context .......................................................................................................... 217
19.20. chcon ....................................................................................................................................... 217
19.21. an example .............................................................................................................................. 218
19.22. setroubleshoot .......................................................................................................................... 220
19.23. booleans ................................................................................................................................... 222
208
Chapter 19. introduction to SELinux
Security Enhanced Linux or SELinux is a set of modifications developed by the United
States National Security Agency (NSA) to provide a variety of security policies for Linux.
SELinux was released as open source at the end of 2000. Since kernel version 2.6 it is an
integrated part of Linux.
SELinux offers security! SELinux can control what kind of access users have to files and
processes. Even when a file received chmod 777, SELinux can still prevent applications
from accessing it (Unix file permissions are checked first!). SELinux does this by placing
users in roles that represent a security context. Administrators have very strict control on
access permissions granted to roles.
SELinux is present in the latest versions of Red Hat Enterprise Linux, Debian, CentOS,
Fedora, and many other distributions..
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19.1. selinux modes
selinux knows three modes: enforcing, permissive and disabled. The enforcing mode will
enforce policies, and may deny access based on selinux rules. The permissive mode will not
enforce policies, but can still log actions that would have been denied in enforcing mode.
The disabled mode disables selinux.
19.2. logging
Verify that syslog is running and activated on boot to enable logging of deny messages in
/var/log/messages.
[root@rhel55 ~]# chkconfig --list syslog
syslog 0:off 1:off 2:on 3:on 4:on 5:on 6:off
Verify that auditd is running and activated on boot to enable logging of easier to read
messages in /var/log/audit/audit.log.
[root@rhel55 ~]# chkconfig --list auditd
auditd 0:off 1:off 2:on 3:on 4:on 5:on 6:off
If not activated, then run chkconfig --levels 2345 auditd on and service auditd start.
[root@rhel55 ~]# service auditd status
auditd (pid 1660) is running...
[root@rhel55 ~]# service syslog status
syslogd (pid 1688) is running...
klogd (pid 1691) is running...
The /var/log/messages log file will tell you that selinux is disabled.
root@deb503:~# grep -i selinux /var/log/messages
Jun 25 15:59:34 deb503 kernel: [ 0.084083] SELinux: Disabled at boot.
Or that it is enabled.
root@deb503:~# grep SELinux /var/log/messages | grep -i Init
Jun 25 15:09:52 deb503 kernel: [ 0.084094] SELinux: Initializing.
19.3. activating selinux
On RHEL you can use the GUI tool to activate selinux, on Debian there is the selinux-
activate command. Activation requires a reboot.
root@deb503:~# selinux-activate
Activating SE Linux
Searching for GRUB installation directory ... found: /boot/grub
Searching for default file ... found: /boot/grub/default
Testing for an existing GRUB menu.lst file ... found: /boot/grub/menu.lst
Searching for splash image ... none found, skipping ...
Found kernel: /boot/vmlinuz-2.6.26-2-686
Updating /boot/grub/menu.lst ... done
SE Linux is activated. You may need to reboot now.
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19.4. getenforce
Use getenforce to verify whether selinux is enforced, disabled or permissive.
[root@rhel55 ~]# getenforce
Permissive
The /selinux/enforce file contains 1 when enforcing, and 0 when permissive mode is active.
root@fedora13 ~# cat /selinux/enforce
1root@fedora13 ~#
19.5. setenforce
You can use setenforce to switch between the Permissive or the Enforcing state once
selinux is activated..
[root@rhel55 ~]# setenforce Enforcing
[root@rhel55 ~]# getenforce
Enforcing
[root@rhel55 ~]# setenforce Permissive
[root@rhel55 ~]# getenforce
Permissive
Or you could just use 0 and 1 as argument.
[root@centos65 ~]# setenforce 1
[root@centos65 ~]# getenforce
Enforcing
[root@centos65 ~]# setenforce 0
[root@centos65 ~]# getenforce
Permissive
[root@centos65 ~]#
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19.6. sestatus
You can see the current selinux status and policy with the sestatus command.
[root@rhel55 ~]# sestatus
SELinux status: enabled
SELinuxfs mount: /selinux
Current mode: permissive
Mode from config file: permissive
Policy version: 21
Policy from config file: targeted
19.7. policy
Most Red Hat server will have the targeted policy. Only NSA/FBI/CIA/DOD/HLS use the
mls policy.
The targted policy will protect hundreds of processes, but lets other processes run
'unconfined' (= they can do anything).
19.8. /etc/selinux/config
The main configuration file for selinux is /etc/selinux/config. When in permissive mode,
the file looks like this.
The targeted policy is selected in /etc/selinux/config.
[root@centos65 ~]# cat /etc/selinux/config
# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
# enforcing - SELinux security policy is enforced.
# permissive - SELinux prints warnings instead of enforcing.
# disabled - SELinux is fully disabled.
SELINUX=permissive
# SELINUXTYPE= type of policy in use. Possible values are:
# targeted - Only targeted network daemons are protected.
# strict - Full SELinux protection.
SELINUXTYPE=targeted
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19.9. DAC or MAC
Standard Unix permissions use Discretionary Access Control to set permissions on files.
This means that a user that owns a file, can make it world readable by typing chmod 777
$file.
With selinux the kernel will enforce Mandatory Access Control which strictly controls
what processes or threads can do with files (superseding DAC). Processes are confined by
the kernel to the minimum access they require.
SELinux MAC is about labeling and type enforcing! Files, processes, etc are all labeled with
an SELinux context. For files, these are extended attributes, for processes this is managed
by the kernel.
The format of the labels is as follows:
user:role:type:(level)
We only use the type label in the targeted policy.
19.10. ls -Z
To see the DAC permissions on a file, use ls -l to display user and group owner and
permissions.
For MAC permissions there is new -Z option added to ls. The output shows that file in /root
have a XXXtype of admin_home_t.
[root@centos65 ~]# ls -Z
-rw-------. root root system_u:object_r:admin_home_t:s0 anaconda-ks.cfg
-rw-r--r--. root root system_u:object_r:admin_home_t:s0 install.log
-rw-r--r--. root root system_u:object_r:admin_home_t:s0 install.log.syslog
[root@centos65 ~]# useradd -m -s /bin/bash pol
[root@centos65 ~]# ls -Z /home/pol/.bashrc
-rw-r--r--. pol pol unconfined_u:object_r:user_home_t:s0 /home/pol/.bashrc
19.11. -Z
There are also some other tools with the -Z switch:
mkdir -Z
cp -Z
ps -Z
netstat -Z
...
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19.12. /selinux
When selinux is active, there is a new virtual file system named /selinux. (You can compare
it to /proc and /dev.)
[root@centos65 ~]# ls -l /selinux/
total 0
-rw-rw-rw-. 1 root root 0 Apr 12 19:40 access
dr-xr-xr-x. 2 root root 0 Apr 12 19:40 avc
dr-xr-xr-x. 2 root root 0 Apr 12 19:40 booleans
-rw-r--r--. 1 root root 0 Apr 12 19:40 checkreqprot
dr-xr-xr-x. 83 root root 0 Apr 12 19:40 class
--w-------. 1 root root 0 Apr 12 19:40 commit_pending_bools
-rw-rw-rw-. 1 root root 0 Apr 12 19:40 context
-rw-rw-rw-. 1 root root 0 Apr 12 19:40 create
-r--r--r--. 1 root root 0 Apr 12 19:40 deny_unknown
--w-------. 1 root root 0 Apr 12 19:40 disable
-rw-r--r--. 1 root root 0 Apr 12 19:40 enforce
dr-xr-xr-x. 2 root root 0 Apr 12 19:40 initial_contexts
-rw-------. 1 root root 0 Apr 12 19:40 load
-rw-rw-rw-. 1 root root 0 Apr 12 19:40 member
-r--r--r--. 1 root root 0 Apr 12 19:40 mls
crw-rw-rw-. 1 root root 1, 3 Apr 12 19:40 null
-r--------. 1 root root 0 Apr 12 19:40 policy
dr-xr-xr-x. 2 root root 0 Apr 12 19:40 policy_capabilities
-r--r--r--. 1 root root 0 Apr 12 19:40 policyvers
-r--r--r--. 1 root root 0 Apr 12 19:40 reject_unknown
-rw-rw-rw-. 1 root root 0 Apr 12 19:40 relabel
-r--r--r--. 1 root root 0 Apr 12 19:40 status
-rw-rw-rw-. 1 root root 0 Apr 12 19:40 user
Although some files in /selinux appear wih size 0, they often contain a boolean value. Check
/selinux/enforce to see if selinux is running in enforced mode.
[root@RHEL5 ~]# ls -l /selinux/enforce
-rw-r--r-- 1 root root 0 Apr 29 08:21 /selinux/enforce
[root@RHEL5 ~]# echo $(cat /selinux/enforce)
1
19.13. identity
The SELinux Identity of a user is distinct from the user ID. An identity is part of a security
context, and (via domains) determines what you can do. The screenshot shows user root
having identity user_u.
[root@rhel55 ~]# id -Z
user_u:system_r:unconfined_t
19.14. role
The selinux role defines the domains that can be used. A role is denied to enter a domain,
unless the role is explicitely authorized to do so.
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19.15. type (or domain)
The selinux context is the security context of a process. An selinux type determines what a
process can do. The screenshot shows init running in type init_t and the mingetty's running
in type getty_t.
[root@centos65 ~]# ps fax -Z | grep /sbin/init
system_u:system_r:init_t:s0 1 ? Ss 0:00 /sbin/init
[root@centos65 ~]# ps fax -Z | grep getty_t
system_u:system_r:getty_t:s0 1307 tty1 Ss+ 0:00 /sbin/mingetty /dev/tty1
system_u:system_r:getty_t:s0 1309 tty2 Ss+ 0:00 /sbin/mingetty /dev/tty2
system_u:system_r:getty_t:s0 1311 tty3 Ss+ 0:00 /sbin/mingetty /dev/tty3
system_u:system_r:getty_t:s0 1313 tty4 Ss+ 0:00 /sbin/mingetty /dev/tty4
system_u:system_r:getty_t:s0 1320 tty5 Ss+ 0:00 /sbin/mingetty /dev/tty5
system_u:system_r:getty_t:s0 1322 tty6 Ss+ 0:00 /sbin/mingetty /dev/tty6
The selinux type is similar to an selinux domain, but refers to directories and files instead
of processes.
Hundreds of binaries also have a type:
[root@centos65 sbin]# ls -lZ useradd usermod userdel httpd postcat postfix
-rwxr-xr-x. root root system_u:object_r:httpd_exec_t:s0 httpd
-rwxr-xr-x. root root system_u:object_r:postfix_master_exec_t:s0 postcat
-rwxr-xr-x. root root system_u:object_r:postfix_master_exec_t:s0 postfix
-rwxr-x---. root root system_u:object_r:useradd_exec_t:s0 useradd
-rwxr-x---. root root system_u:object_r:useradd_exec_t:s0 userdel
-rwxr-x---. root root system_u:object_r:useradd_exec_t:s0 usermod
Ports also have a context.
[root@centos65 sbin]# netstat -nptlZ | tr -s ' ' | cut -d' ' -f6-
Foreign Address State PID/Program name Security Context
LISTEN 1096/rpcbind system_u:system_r:rpcbind_t:s0
LISTEN 1208/sshd system_u:system_r:sshd_t:s0-s0:c0.c1023
LISTEN 1284/master system_u:system_r:postfix_master_t:s0
LISTEN 1114/rpc.statd system_u:system_r:rpcd_t:s0
LISTEN 1096/rpcbind system_u:system_r:rpcbind_t:s0
LISTEN 1666/httpd unconfined_u:system_r:httpd_t:s0
LISTEN 1208/sshd system_u:system_r:sshd_t:s0-s0:c0.c1023
LISTEN 1114/rpc.statd system_u:system_r:rpcd_t:s0
LISTEN 1284/master system_u:system_r:postfix_master_t:s0
You can also get a list of ports that are managed by SELinux:
[root@centos65 ~]# semanage port -l | tail
xfs_port_t tcp 7100
xserver_port_t tcp 6000-6150
zabbix_agent_port_t tcp 10050
zabbix_port_t tcp 10051
zarafa_port_t tcp 236, 237
zebra_port_t tcp 2600-2604, 2606
zebra_port_t udp 2600-2604, 2606
zented_port_t tcp 1229
zented_port_t udp 1229
zope_port_t tcp 8021
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19.16. security context
The combination of identity, role and domain or type make up the selinux security context.
The id will show you your security context in the form identity:role:domain.
[paul@RHEL5 ~]$ id | cut -d' ' -f4
context=user_u:system_r:unconfined_t
The ls -Z command shows the security context for a file in the form identity:role:type.
[paul@RHEL5 ~]$ ls -Z test
-rw-rw-r-- paul paul user_u:object_r:user_home_t test
The security context for processes visible in /proc defines both the type (of the file in /proc)
and the domain (of the running process). Let's take a look at the init process and /proc/1/ .
The init process runs in domain init_t.
[root@RHEL5 ~]# ps -ZC init
LABEL PID TTY TIME CMD
system_u:system_r:init_t 1 ? 00:00:01 init
The /proc/1/ directory, which identifies the init process, has type init_t.
[root@RHEL5 ~]# ls -Zd /proc/1/
dr-xr-xr-x root root system_u:system_r:init_t /proc/1/
It is not a coincidence that the domain of the init process and the type of /proc/1/ are both
init_t.
Don't try to use chcon on /proc! It will not work.
19.17. transition
An selinux transition (aka an selinux labelling) determines the security context that will be
assigned. A transition of process domains is used when you execute a process. A transition
of file type happens when you create a file.
An example of file type transition.
[pol@centos65 ~]$ touch test /tmp/test
[pol@centos65 ~]$ ls -Z test
-rw-rw-r--. pol pol unconfined_u:object_r:user_home_t:s0 test
[pol@centos65 ~]$ ls -Z /tmp/test
-rw-rw-r--. pol pol unconfined_u:object_r:user_tmp_t:s0 /tmp/test
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19.18. extended attributes
Extended attributes are used by selinux to store security contexts. These attributes can be
viewed with ls when selinux is running.
[root@RHEL5 home]# ls --context
drwx------ paul paul system_u:object_r:user_home_dir_t paul
drwxr-xr-x root root user_u:object_r:user_home_dir_t project42
drwxr-xr-x root root user_u:object_r:user_home_dir_t project55
[root@RHEL5 home]# ls -Z
drwx------ paul paul system_u:object_r:user_home_dir_t paul
drwxr-xr-x root root user_u:object_r:user_home_dir_t project42
drwxr-xr-x root root user_u:object_r:user_home_dir_t project55
[root@RHEL5 home]#
When selinux is not running, then getfattr is the tool to use.
[root@RHEL5 etc]# getfattr -m . -d hosts
# file: hosts
security.selinux="system_u:object_r:etc_t:s0\000"
19.19. process security context
A new option is added to ps to see the selinux security context of processes.
[root@RHEL5 etc]# ps -ZC mingetty
LABEL PID TTY TIME CMD
system_u:system_r:getty_t 2941 tty1 00:00:00 mingetty
system_u:system_r:getty_t 2942 tty2 00:00:00 mingetty
19.20. chcon
Use chcon to change the selinux security context.
This example shows how to use chcon to change the type of a file.
[root@rhel55 ~]# ls -Z /var/www/html/test42.txt
-rw-r--r-- root root user_u:object_r:httpd_sys_content_t /var/www/html/test4\
2.txt
[root@rhel55 ~]# chcon -t samba_share_t /var/www/html/test42.txt
[root@rhel55 ~]# ls -Z /var/www/html/test42.txt
-rw-r--r-- root root user_u:object_r:samba_share_t /var/www/html/test42.txt
Be sure to read man chcon.
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introduction to SELinux
19.21. an example
The Apache2 webserver is by default targeted with SELinux. The next screenshot shows
that any file created in /var/www/html will by default get the httpd_sys_content_t type.
[root@centos65 ~]# touch /var/www/html/test42.txt
[root@centos65 ~]# ls -Z /var/www/html/test42.txt
-rw-r--r--. root root unconfined_u:object_r:httpd_sys_content_t:s0 /var/www/h\
tml/test42.txt
Files created elsewhere do not get this type.
[root@centos65 ~]# touch /root/test42.txt
[root@centos65 ~]# ls -Z /root/test42.txt
-rw-r--r--. root root unconfined_u:object_r:admin_home_t:s0 /root/test42.txt
Make sure Apache2 runs.
[root@centos65 ~]# service httpd restart
Stopping httpd: [ OK ]
Starting httpd: [ OK ]
Will this work ? Yes it does.
[root@centos65 ~]# wget http://localhost/test42.txt
--2014-04-12 20:56:47-- http://localhost/test42.txt
Resolving localhost... ::1, 127.0.0.1
Connecting to localhost|::1|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 0 [text/plain]
Saving to: “test42.txt”
...
Why does this work ? Because Apache2 runs in the httpd_t domain and the files in /var/
www/html have the httpd_sys_content_t type.
[root@centos65 ~]# ps -ZC httpd | head -4
LABEL PID TTY TIME CMD
unconfined_u:system_r:httpd_t:s0 1666 ? 00:00:00 httpd
unconfined_u:system_r:httpd_t:s0 1668 ? 00:00:00 httpd
unconfined_u:system_r:httpd_t:s0 1669 ? 00:00:00 httpd
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introduction to SELinux
So let's set SELinux to enforcing and change the type of this file.
[root@centos65 ~]# chcon -t samba_share_t /var/www/html/test42.txt
[root@centos65 ~]# ls -Z /var/www/html/test42.txt
-rw-r--r--. root root unconfined_u:object_r:samba_share_t:s0 /var/www/html/t\
est42.txt
[root@centos65 ~]# setenforce 1
[root@centos65 ~]# getenforce
Enforcing
There are two possibilities now: either it works, or it fails. It works when selinux is in
permissive mode, it fails when in enforcing mode.
[root@centos65 ~]# wget http://localhost/test42.txt
--2014-04-12 21:05:02-- http://localhost/test42.txt
Resolving localhost... ::1, 127.0.0.1
Connecting to localhost|::1|:80... connected.
HTTP request sent, awaiting response... 403 Forbidden
2014-04-12 21:05:02 ERROR 403: Forbidden.
The log file gives you a cryptic message...
[root@centos65 ~]# tail -3 /var/log/audit/audit.log
type=SYSCALL msg=audit(1398200702.803:64): arch=c000003e syscall=4 succ\
ess=no exit=-13 a0=7f5fbc334d70 a1=7fff553b4f10 a2=7fff553b4f10 a3=0 it\
ems=0 ppid=1666 pid=1673 auid=500 uid=48 gid=48 euid=48 suid=48 fsuid=4\
8 egid=48 sgid=48 fsgid=48 tty=(none) ses=1 comm="httpd" exe="/usr/sbin\
/httpd" subj=unconfined_u:system_r:httpd_t:s0 key=(null)
type=AVC msg=audit(1398200702.804:65): avc: denied { getattr } for p\
id=1673 comm="httpd" path="/var/www/html/test42.txt" dev=dm-0 ino=26324\
1 scontext=unconfined_u:system_r:httpd_t:s0 tcontext=unconfined_u:objec\
t_r:samba_share_t:s0 tclass=file
type=SYSCALL msg=audit(1398200702.804:65): arch=c000003e syscall=6 succ\
ess=no exit=-13 a0=7f5fbc334e40 a1=7fff553b4f10 a2=7fff553b4f10 a3=1 it\
ems=0 ppid=1666 pid=1673 auid=500 uid=48 gid=48 euid=48 suid=48 fsuid=4\
8 egid=48 sgid=48 fsgid=48 tty=(none) ses=1 comm="httpd" exe="/usr/sbin\
/httpd" subj=unconfined_u:system_r:httpd_t:s0 key=(null)
And /var/log/messages mentions nothing of the failed download.
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introduction to SELinux
19.22. setroubleshoot
The log file above was not very helpful, but these two packages can make your life much
easier.
[root@centos65 ~]# yum -y install setroubleshoot setroubleshoot-server
You need to reboot for this to work...
So we reboot, restart the httpd server, reactive SELinux Enforce, and do the wget again...
and it fails (because of SELinux).
[root@centos65 ~]# service httpd restart
Stopping httpd: [FAILED]
Starting httpd: [ OK ]
[root@centos65 ~]# getenforce
Permissive
[root@centos65 ~]# setenforce 1
[root@centos65 ~]# getenforce
Enforcing
[root@centos65 ~]# wget http://localhost/test42.txt
--2014-04-12 21:44:13-- http://localhost/test42.txt
Resolving localhost... ::1, 127.0.0.1
Connecting to localhost|::1|:80... connected.
HTTP request sent, awaiting response... 403 Forbidden
2014-04-12 21:44:13 ERROR 403: Forbidden.
The /var/log/audit/ is still not out best friend, but take a look at /var/log/messages.
[root@centos65 ~]# tail -2 /var/log/messages
Apr 12 21:44:16 centos65 setroubleshoot: SELinux is preventing /usr/sbin/h\
ttpd from getattr access on the file /var/www/html/test42.txt. For complete \
SELinux messages. run sealert -l b2a84386-54c1-4344-96fb-dcf969776696
Apr 12 21:44:16 centos65 setroubleshoot: SELinux is preventing /usr/sbin/h\
ttpd from getattr access on the file /var/www/html/test42.txt. For complete \
SELinux messages. run sealert -l b2a84386-54c1-4344-96fb-dcf969776696
So we run the command it suggests...
[root@centos65 ~]# sealert -l b2a84386-54c1-4344-96fb-dcf969776696
SELinux is preventing /usr/sbin/httpd from getattr access on the file /va\
r/www/html/test42.txt.
***** Plugin restorecon (92.2 confidence) suggests *********************
If you want to fix the label.
/var/www/html/test42.txt default label should be httpd_sys_content_t.
Then you can run restorecon.
Do
# /sbin/restorecon -v /var/www/html/test42.txt
...
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introduction to SELinux
We follow the friendly advice and try again to download our file:
[root@centos65 ~]# /sbin/restorecon -v /var/www/html/test42.txt
/sbin/restorecon reset /var/www/html/test42.txt context unconfined_u:objec\
t_r:samba_share_t:s0->unconfined_u:object_r:httpd_sys_content_t:s0
[root@centos65 ~]# wget http://localhost/test42.txt
--2014-04-12 21:54:03-- http://localhost/test42.txt
Resolving localhost... ::1, 127.0.0.1
Connecting to localhost|::1|:80... connected.
HTTP request sent, awaiting response... 200 OK
It works!
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introduction to SELinux
19.23. booleans
Booleans are on/off switches
[root@centos65 ~]# getsebool -a | head
abrt_anon_write --> off
abrt_handle_event --> off
allow_console_login --> on
allow_cvs_read_shadow --> off
allow_daemons_dump_core --> on
allow_daemons_use_tcp_wrapper --> off
allow_daemons_use_tty --> on
allow_domain_fd_use --> on
allow_execheap --> off
allow_execmem --> on
You can set and read individual booleans.
[root@centos65 ~]# setsebool httpd_read_user_content=1
[root@centos65 ~]# getsebool httpd_read_user_content
httpd_read_user_content --> on
[root@centos65 ~]# setsebool httpd_enable_homedirs=1
[root@centos65 ~]# getsebool httpd_enable_homedirs
httpd_enable_homedirs --> on
You can set these booleans permanent.
[root@centos65 ~]# setsebool -P httpd_enable_homedirs=1
[root@centos65 ~]# setsebool -P httpd_read_user_content=1
The above commands regenerate the complete /etc/selinux/targeted directory!
[root@centos65 ~]# cat /etc/selinux/targeted/modules/active/booleans.local
# This file is auto-generated by libsemanage
# Do not edit directly.
httpd_enable_homedirs=1
httpd_read_user_content=1
222
Part VIII. introducing git
Table of Contents
20. git ........................................................................................................................................................... 225
20.1. git ............................................................................................................................................... 226
20.2. installing git .............................................................................................................................. 227
20.3. starting a project ....................................................................................................................... 227
20.4. git branches ............................................................................................................................... 230
20.5. to be continued... ....................................................................................................................... 231
20.6. github.com ................................................................................................................................. 232
20.7. add your public key to github .................................................................................................. 232
20.8. practice: git ................................................................................................................................ 233
224
Chapter 20. git
This chapter is an introduction to using git on the command line. The git repository is hosted
by github, but you are free to choose another server (or create your own).
There are many excellent online tutorials for git. This list can save you one Google query:
http://gitimmersion.com/
http://git-scm.com/book
225
git
20.1. git
Linus Torvalds created git back in 2005 when Bitkeeper changed its license and the Linux
kernel developers where no longer able to use it for free.
git quickly became popular and is now the most widely used distributed version control
system in the world.
Geek and Poke demonstrates why we need version control (image property of Geek and
Poke CCA 3.0).
Besides source code for software, you can also find German and Icelandic law on github
(and probably much more by the time you are reading this).
226
git
20.2. installing git
We install git with aptitude install git as seen in this screenshot on Debian 6.
root@debian6:~# aptitude install git
The following NEW packages will be installed:
git libcurl3-gnutls{a} liberror-perl{a}
0 packages upgraded, 3 newly installed, 0 to remove and 0 not upgraded.
...
Processing triggers for man-db ...
Setting up libcurl3-gnutls (7.21.0-2.1+squeeze2) ...
Setting up liberror-perl (0.17-1) ...
Setting up git (1:1.7.2.5-3) ...
20.3. starting a project
First we create a project directory, with a simple file in it.
paul@debian6~$ mkdir project42
paul@debian6~$ cd project42/
paul@debian6~/project42$ echo "echo The answer is 42." >> question.sh
20.3.1. git init
Then we tell git to create an empty git repository in this directory.
paul@debian6~/project42$ ls -la
total 12
drwxrwxr-x 2 paul paul 4096 Dec 8 16:41 .
drwxr-xr-x 46 paul paul 4096 Dec 8 16:41 ..
-rw-rw-r-- 1 paul paul 23 Dec 8 16:41 question.sh
paul@debian6~/project42$ git init
Initialized empty Git repository in /home/paul/project42/.git/
paul@debian6~/project42$ ls -la
total 16
drwxrwxr-x 3 paul paul 4096 Dec 8 16:44 .
drwxr-xr-x 46 paul paul 4096 Dec 8 16:41 ..
drwxrwxr-x 7 paul paul 4096 Dec 8 16:44 .git
-rw-rw-r-- 1 paul paul 23 Dec 8 16:41 question.sh
20.3.2. git config
Next we use git config to set some global options.
paul@debian6$ git config --global user.name Paul
paul@debian6$ git config --global user.email "paul.cobbaut@gmail.com"
paul@debian6$ git config --global core.editor vi
We can verify this config in ~/.gitconfig:
paul@debian6~/project42$ cat ~/.gitconfig
[user]
name = Paul
email = paul.cobbaut@gmail.com
[core]
editor = vi
20.3.3. git add
Time now to add file to our project with git add, and verify that it is added with git status.
227
git
paul@debian6~/project42$ git add question.sh
paul@debian6~/project42$ git status
# On branch master
#
# Initial commit
#
# Changes to be committed:
# (use "git rm --cached <file>..." to unstage)
#
# new file: question.sh
#
The git status tells us there is a new file ready to be committed.
20.3.4. git commit
With git commit you force git to record all added files (and all changes to those files)
permanently.
paul@debian6~/project42$ git commit -m "starting a project"
[master (root-commit) 5c10768] starting a project
1 file changed, 1 insertion(+)
create mode 100644 question.sh
paul@debian6~/project42$ git status
# On branch master
nothing to commit (working directory clean)
20.3.5. changing a committed file
The screenshots below show several steps. First we change a file:
paul@debian6~/project42$ git status
# On branch master
nothing to commit (working directory clean)
paul@debian6~/project42$ vi question.sh
Then we verify the status and see that it is modified:
paul@debian6~/project42$ git status
# On branch master
# Changes not staged for commit:
# (use "git add <file>..." to update what will be committed)
# (use "git checkout -- <file>..." to discard changes in working directory)
#
# modified: question.sh
#
no changes added to commit (use "git add" and/or "git commit -a")
Next we add it to the git repository.
paul@debian6~/project42$ git add question.sh
paul@debian6~/project42$ git commit -m "adding a she-bang to the main script"
[master 86b8347] adding a she-bang to the main script
1 file changed, 1 insertion(+)
paul@debian6~/project42$ git status
# On branch master
nothing to commit (working directory clean)
20.3.6. git log
We can see all our commits again using git log.
228
git
paul@debian6~/project42$ git log
commit 86b8347192ea025815df7a8e628d99474b41fb6c
Author: Paul <paul.cobbaut@gmail.com>
Date: Sat Dec 8 17:12:24 2012 +0100
adding a she-bang to the main script
commit 5c10768f29aecc16161fb197765e0f14383f7bca
Author: Paul <paul.cobbaut@gmail.com>
Date: Sat Dec 8 17:09:29 2012 +0100
starting a project
The log format can be changed.
paul@debian6~/project42$ git log --pretty=oneline
86b8347192ea025815df7a8e628d99474b41fb6c adding a she-bang to the main script
5c10768f29aecc16161fb197765e0f14383f7bca starting a project
The log format can be customized a lot.
paul@debian6~/project42$ git log --pretty=format:"%an: %ar :%s"
Paul: 8 minutes ago :adding a she-bang to the main script
Paul: 11 minutes ago :starting a project
20.3.7. git mv
Renaming a file can be done with mv followed by a git remove and a git add of the new
filename. But it can be done easier and in one command using git mv.
paul@debian6~/project42$ git mv question.sh thequestion.sh
paul@debian6~/project42$ git status
# On branch master
# Changes to be committed:
# (use "git reset HEAD <file>..." to unstage)
#
# renamed: question.sh -> thequestion.sh
#
paul@debian6~/project42$ git commit -m "improved naming scheme"
[master 69b2c8b] improved naming scheme
1 file changed, 0 insertions(+), 0 deletions(-)
rename question.sh => thequestion.sh (100%)
229
git
20.4. git branches
Working on the project can be done in one or more git branches. Here we create a new
branch that will make changes to the script. We will merge this branch with the master
branch when we are sure the script works. (It can be useful to add git status commands
when practicing).
paul@debian6~/project42$ git branch
* master
paul@debian6~/project42$ git checkout -b newheader
Switched to a new branch 'newheader'
paul@debian6~/project42$ vi thequestion.sh
paul@debian6~/project42$ git add thequestion.sh
paul@debian6~/project42$ source thequestion.sh
The answer is 42.
It seems to work, so we commit in this branch.
paul@debian6~/project42$ git commit -m "adding a new company header"
[newheader 730a22b] adding a new company header
1 file changed, 4 insertions(+)
paul@debian6~/project42$ git branch
master
* newheader
paul@debian6~/project42$ cat thequestion.sh
#!/bin/bash
#
# copyright linux-training.be
#
echo The answer is 42.
Let us go back to the master branch and see what happened there.
paul@debian6~/project42$ git checkout master
Switched to branch 'master'
paul@debian6~/project42$ cat thequestion.sh
#!/bin/bash
echo The answer is 42.
Nothing happened in the master branch, because we worked in another branch.
When we are sure the branch is ready for production, then we merge it into the master branch.
paul@debian6~/project42$ cat thequestion.sh
#!/bin/bash
echo The answer is 42.
paul@debian6~/project42$ git merge newheader
Updating 69b2c8b..730a22b
Fast-forward
thequestion.sh | 4 ++++
1 file changed, 4 insertions(+)
paul@debian6~/project42$ cat thequestion.sh
#!/bin/bash
#
# copyright linux-training.be
#
echo The answer is 42.
The newheader branch can now be deleted.
230
git
paul@debian6~/project42$ git branch
* master
newheader
paul@debian6~/project42$ git branch -d newheader
Deleted branch newheader (was 730a22b).
paul@debian6~/project42$ git branch
* master
20.5. to be continued...
The git story is not finished.
There are many excellent online tutorials for git. This list can save you one Google query:
http://gitimmersion.com/
http://git-scm.com/book
231
git
20.6. github.com
Create an account on github.com. This website is a frontend for an immense git server with
over two and a half million users and almost five million projects (including Fedora, Linux
kernel, Android, Ruby on Rails, Wine, X.org, VLC...)
https://github.com/signup/free
This account is free of charge, we will use it in the examples below.
20.7. add your public key to github
I prefer to use github with a public key, so it probably is a good idea that you also upload
your public key to github.com.
You can upload your own key via the web interface:
https://github.com/settings/ssh
Please do not forget to protect your private key!
232
git
20.8. practice: git
1. Create a project on github to host a script that you wrote. Have at least two other people
improve the script.
233
Part IX. ipv6
Table of Contents
21. Introduction to ipv6 ............................................................................................................................ 236
21.1. about ipv6 .................................................................................................................................. 237
21.2. network id and host id .............................................................................................................. 237
21.3. host part generation ................................................................................................................... 237
21.4. ipv4 mapped ipv6 address ........................................................................................................ 238
21.5. link local addresses ................................................................................................................... 238
21.6. unique local addresses .............................................................................................................. 238
21.7. globally unique unicast addresses ............................................................................................. 238
21.8. 6to4 ............................................................................................................................................ 238
21.9. ISP ............................................................................................................................................. 239
21.10. non routable addresses ............................................................................................................ 239
21.11. ping6 ........................................................................................................................................ 239
21.12. Belgium and ipv6 .................................................................................................................... 240
21.13. other websites .......................................................................................................................... 240
21.14. 6to4 gateways .......................................................................................................................... 242
21.15. ping6 and dns .......................................................................................................................... 242
21.16. ipv6 and tcp/http ..................................................................................................................... 242
21.17. ipv6 PTR record ...................................................................................................................... 242
21.18. 6to4 setup on Linux ................................................................................................................ 242
235
Chapter 21. Introduction to ipv6
236
Introduction to ipv6
21.1. about ipv6
The ipv6 protocol is designed to replace ipv4. Where ip version 4 supports a maximum
of four billion unique addresses, ip version 6 expands this to four billion times four
billion times four billion times four billion unique addresses. This is more than
100.000.000.000.000.000.000 ipv6 addresses per square cm on our planet. That should be
enough, even if every cell phone, every coffee machine and every pair of socks gets an
address.
Technically speaking ipv6 uses 128-bit addresses (instead of the 32-bit from ipv4). 128-bit
addresses are huge numbers. In decimal it would amount up to 39 digits, in hexadecimal
it looks like this:
fe80:0000:0000:0000:0a00:27ff:fe8e:8aa8
Luckily ipv6 allows us to omit leading zeroes. Our address from above then becomes:
fe80:0:0:0:a00:27ff:fe8e:8aa8
When a 16-bit block is zero, it can be written as ::. Consecutive 16-bit blocks that are zero
can also be written as ::. So our address can from above can be shortened to:
fe80::a00:27ff:fe8e:8aa8
This :: can only occur once! The following is not a valid ipv6 address:
fe80::20:2e4f::39ac
The ipv6 localhost address is 0000:0000:0000:0000:0000:0000:0000:0001, which can be
abbreviated to ::1.
paul@debian5:~/github/lt/images$ /sbin/ifconfig lo | grep inet6
inet6 addr: ::1/128 Scope:Host
21.2. network id and host id
One of the few similarities between ipv4 and ipv6 is that addresses have a host part and a
network part determined by a subnet mask. Using the cidr notation this looks like this:
fe80::a00:27ff:fe8e:8aa8/64
The above address has 64 bits for the host id, theoretically allowing for 4 billion times four
billion hosts.
The localhost address looks like this with cidr:
::1/128
21.3. host part generation
The host part of an automatically generated (stateless) ipv6 address contains part of the hosts
mac address:
paul@debian5:~$ /sbin/ifconfig | head -3
237
Introduction to ipv6
eth3 Link encap:Ethernet HWaddr 08:00:27:ab:67:30
inet addr:192.168.1.29 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::a00:27ff:feab:6730/64 Scope:Link
Some people are concerned about privacy here...
21.4. ipv4 mapped ipv6 address
Some applications use ipv4 addresses embedded in an ipv6 address. (Yes there will be an
era of migration with both ipv4 and ipv6 in use.) The ipv6 address then looks like this:
::ffff:192.168.1.42/96
Indeed a mix of decimal and hexadecimal characters...
21.5. link local addresses
ipv6 addresses starting with fe8. can only be used on the local segment (replace the dot with
an hexadecimal digit). This is the reason you see Scope:Link behind the address in this
screenshot. This address serves only the local link.
paul@deb503:~$ /sbin/ifconfig | grep inet6
inet6 addr: fe80::a00:27ff:fe8e:8aa8/64 Scope:Link
inet6 addr: ::1/128 Scope:Host
These link local addresses all begin with fe8..
Every ipv6 enabled nic will get an address in this range.
21.6. unique local addresses
The now obsolete system of site local addresses similar to ipv4 private ranges is replaced
with a system of globally unique local ipv6 addresses. This to prevent duplicates when
joining of networks within site local ranges.
All unique local addresses strat with fd...
21.7. globally unique unicast addresses
Since ipv6 was designed to have multiple ip addresses per interface, the global ipv6 address
can be used next to the link local address.
These globally unique addresses all begin with 2... or 3... as the first 16-bits.
21.8. 6to4
6to4 is defined in rfc's 2893 and 3056 as one possible way to transition between ipv4 and
ipv6 by creating an ipv6 tunnel.
It encodes an ipv4 address in an ipv6 address that starts with 2002. For example
192.168.1.42/24 will be encoded as:
238
Introduction to ipv6
2002:c0a8:12a:18::1
You can use the command below to convert any ipv4 address to this range.
paul@ubu1010:~$ printf "2002:%02x%02x:%02x%02x:%04x::1\n" `echo 192.168.1.42/24 \
|tr "./" " "`
2002:c0a8:012a:0018::1
21.9. ISP
Should you be so lucky to get an ipv6 address from an isp, then it will start with 2001:.
21.10. non routable addresses
Comparable to example.com for DNS, the following ipv6 address ranges are reserved for
examples, and not routable on the internet.
3fff:ffff::/32
2001:0db8::/32
21.11. ping6
Use ping6 to test connectivity between ipv6 hosts. You need to specify the interface (there
is no routing table for 'random' generated ipv6 link local addresses).
[root@fedora14 ~]# ping6 -I eth0 fe80::a00:27ff:fecd:7ffc
PING fe80::a00:27ff:fecd:7ffc(fe80::a00:27ff:fecd:7ffc) from fe80::a00:27ff:fe3c:4346 eth0: 56
64 bytes from fe80::a00:27ff:fecd:7ffc: icmp_seq=1 ttl=64 time=0.586 ms
64 bytes from fe80::a00:27ff:fecd:7ffc: icmp_seq=2 ttl=64 time=3.95 ms
64 bytes from fe80::a00:27ff:fecd:7ffc: icmp_seq=3 ttl=64 time=1.53 ms
Below a multicast ping6 that recieves replies from three ip6 hosts on the same network.
[root@fedora14 ~]# ping6 -I eth0 ff02::1
PING ff02::1(ff02::1) from fe80::a00:27ff:fe3c:4346 eth0: 56 data bytes
64 bytes from fe80::a00:27ff:fe3c:4346: icmp_seq=1 ttl=64 time=0.598 ms
64 bytes from fe80::a00:27ff:fecd:7ffc: icmp_seq=1 ttl=64 time=1.87 ms (DUP!)
64 bytes from fe80::8e7b:9dff:fed6:dff2: icmp_seq=1 ttl=64 time=535 ms (DUP!)
64 bytes from fe80::a00:27ff:fe3c:4346: icmp_seq=2 ttl=64 time=0.106 ms
64 bytes from fe80::8e7b:9dff:fed6:dff2: icmp_seq=2 ttl=64 time=1.79 ms (DUP!)
64 bytes from fe80::a00:27ff:fecd:7ffc: icmp_seq=2 ttl=64 time=2.48 ms (DUP!)
239
Introduction to ipv6
21.12. Belgium and ipv6
A lot of information on ipv6 in Belgium can be found at www.ipv6council.be.
Sites like ipv6.belgium.be, www.bipt.be and www.bricozone.be are enabled for ipv6. Some
Universities also: fundp.ac.be (Namur) and ulg.ac.be (Liege).
21.13. other websites
Other useful websites for testing ipv6 are:
test-ipv6.com
ipv6-test.com
Going to the ipv6-test.com website will test whether you have a valid accessible ipv6
address.
Going to the test-ipv6.com website will also test whether you have a valid accessible ipv6
address.
240
Introduction to ipv6
241
Introduction to ipv6
21.14. 6to4 gateways
To access ipv4 only websites when on ipv6 you can use sixxs.net (more specifically http://
www.sixxs.net/tools/gateway/) as a gatway.
For example use http://www.slashdot.org.sixxs.org/ instead of http://slashdot.org
21.15. ping6 and dns
Below a screenshot of a ping6 from behind a 6to4 connection.
21.16. ipv6 and tcp/http
Below a screenshot of a tcp handshake and http connection over ipv6.
21.17. ipv6 PTR record
As seen in the DNS chapter, ipv6 PTR records are in the ip6.net domain, and have 32
generations of child domains.
21.18. 6to4 setup on Linux
Below a transcript of a 6to4 setup on Linux.
Thanks to http://www.anyweb.co.nz/tutorial/v6Linux6to4 and http://mirrors.bieringer.de/
Linux+IPv6-HOWTO/ and tldp.org!
root@mac:~# ifconfig
eth0 Link encap:Ethernet HWaddr 00:26:bb:5d:2e:52
inet addr:81.165.101.125 Bcast:255.255.255.255 Mask:255.255.248.0
242
Introduction to ipv6
inet6 addr: fe80::226:bbff:fe5d:2e52/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:5926044 errors:0 dropped:0 overruns:0 frame:0
TX packets:2985892 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:4274849823 (4.2 GB) TX bytes:237002019 (237.0 MB)
Interrupt:43 Base address:0x8000
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:598 errors:0 dropped:0 overruns:0 frame:0
TX packets:598 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:61737 (61.7 KB) TX bytes:61737 (61.7 KB)
root@mac:~# sysctl -w net.ipv6.conf.default.forwarding=1
net.ipv6.conf.default.forwarding = 1
root@mac:~# ip tunnel add tun6to4 mode sit remote any local 81.165.101.125
root@mac:~# ip link set dev tun6to4 mtu 1472 up
root@mac:~# ip link show dev tun6to4
10: tun6to4: <NOARP,UP,LOWER_UP> mtu 1472 qdisc noqueue state UNKNOWN
link/sit 81.165.101.125 brd 0.0.0.0
root@mac:~# ip -6 addr add dev tun6to4 2002:51a5:657d:0::1/64
root@mac:~# ip -6 addr add dev eth0 2002:51a5:657d:1::1/64
root@mac:~# ip -6 addr add dev eth0 fdcb:43c1:9c18:1::1/64
root@mac:~# ifconfig
eth0 Link encap:Ethernet HWaddr 00:26:bb:5d:2e:52
inet addr:81.165.101.125 Bcast:255.255.255.255 Mask:255.255.248.0
inet6 addr: fe80::226:bbff:fe5d:2e52/64 Scope:Link
inet6 addr: fdcb:43c1:9c18:1::1/64 Scope:Global
inet6 addr: 2002:51a5:657d:1::1/64 Scope:Global
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:5927436 errors:0 dropped:0 overruns:0 frame:0
TX packets:2986025 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:4274948430 (4.2 GB) TX bytes:237014619 (237.0 MB)
Interrupt:43 Base address:0x8000
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:598 errors:0 dropped:0 overruns:0 frame:0
TX packets:598 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:61737 (61.7 KB) TX bytes:61737 (61.7 KB)
tun6to4 Link encap:IPv6-in-IPv4
inet6 addr: ::81.165.101.125/128 Scope:Compat
inet6 addr: 2002:51a5:657d::1/64 Scope:Global
UP RUNNING NOARP MTU:1472 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
root@mac:~# ip -6 route add 2002::/16 dev tun6to4
root@mac:~# ip -6 route add ::/0 via ::192.88.99.1 dev tun6to4 metric 1
root@mac:~# ip -6 route show
::/96 via :: dev tun6to4 metric 256 mtu 1472 advmss 1412 hoplimit 0
2002:51a5:657d::/64 dev tun6to4 proto kernel metric 256 mtu 1472 advmss 1412 hoplimit 0
2002:51a5:657d:1::/64 dev eth0 proto kernel metric 256 mtu 1500 advmss 1440 hoplimit 0
243
Introduction to ipv6
2002::/16 dev tun6to4 metric 1024 mtu 1472 advmss 1412 hoplimit 0
fdcb:43c1:9c18:1::/64 dev eth0 proto kernel metric 256 mtu 1500 advmss 1440 hoplimit 0
fe80::/64 dev eth0 proto kernel metric 256 mtu 1500 advmss 1440 hoplimit 0
fe80::/64 dev tun6to4 proto kernel metric 256 mtu 1472 advmss 1412 hoplimit 0
default via ::192.88.99.1 dev tun6to4 metric 1 mtu 1472 advmss 1412 hoplimit 0
root@mac:~# ping6 ipv6-test.com
PING ipv6-test.com(ipv6-test.com) 56 data bytes
64 bytes from ipv6-test.com: icmp_seq=1 ttl=57 time=42.4 ms
64 bytes from ipv6-test.com: icmp_seq=2 ttl=57 time=43.0 ms
64 bytes from ipv6-test.com: icmp_seq=3 ttl=57 time=43.5 ms
64 bytes from ipv6-test.com: icmp_seq=4 ttl=57 time=43.9 ms
64 bytes from ipv6-test.com: icmp_seq=5 ttl=57 time=45.6 ms
^C
--- ipv6-test.com ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4006ms
rtt min/avg/max/mdev = 42.485/43.717/45.632/1.091 ms
244
Part X. Appendices
Table of Contents
A. cloning .................................................................................................................................................... 247
A.1. About cloning ............................................................................................................................. 247
A.2. About offline cloning ................................................................................................................. 247
A.3. Offline cloning example ............................................................................................................ 247
B. License .................................................................................................................................................... 249
246
Appendix A. cloning
A.1. About cloning
You can have distinct goals for cloning a server. For instance a clone can be a cold iron
backup system used for manual disaster recovery of a service. Or a clone can be created to
serve in a test environment. Or you might want to make an almost identical server. Let's take
a look at some offline and online ways to create a clone of a Linux server.
A.2. About offline cloning
The term offline cloning is used when you power off the running Linux server to create the
clone. This method is easy since we don't have to consider open files and we don't have to
skip virtual file systems like /dev or /sys . The offline cloning method can be broken down
into these steps:
1. Boot source and target server with a bootable CD
2. Partition, format and mount volumes on the target server
3. Copy files/partitions from source to target over the network
The first step is trivial. The second step is explained in the Disk Management chapter. For
the third step, you can use a combination of ssh or netcat with cp, dd, dump and restore,
tar, cpio, rsync or even cat.
A.3. Offline cloning example
We have a working Red Hat Enterprise Linux 5 server, and we want a perfect copy of it on
newer hardware. First thing to do is discover the disk layout.
[root@RHEL5 ~]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda2 15G 4.5G 9.3G 33% /
/dev/sda1 99M 31M 64M 33% /boot
The /boot partition is small but big enough. If we create an identical partition, then dd should
be a good cloning option. Suppose the / partition needs to be enlarged on the target system.
The best option then is to use a combination of dump and restore. Remember that dd copies
blocks, whereas dump/restore copies files.
The first step to do is to boot the target server with a live CD and partition the target disk.
To do this we use the Red Hat Enterprise Linux 5 install CD. At the CD boot prompt we
type "linux rescue". The cd boots into a root console where we can use fdisk to discover
and prepare the attached disks.
When the partitions are created and have their filesystem, then we can use dd to copy the /
boot partition.
247
cloning
ssh root@192.168.1.40 "dd if=/dev/sda1" | dd of=/dev/sda1
Then we use a dump and restore combo to copy the / partition.
mkdir /mnt/x
mount /dev/sda2 /mnt/x
cd /mnt/x
ssh root@192.168.1.40 "dump -0 -f - /" | restore -r -f -
248
Appendix B. 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
principally for works whose purpose is instruction or reference.
1. APPLICABILITY AND DEFINITIONS
This License applies to any manual or other work, in any medium, that
contains a notice placed by the copyright holder saying it can be
distributed under the terms of this License. Such a notice grants a
world-wide, royalty-free license, unlimited in duration, to use that
work under the conditions stated herein. The "Document", below, refers
to any such manual or work. Any member of the public is a licensee,
and is addressed as "you". You accept the license if you copy, modify
or distribute the work in a way requiring permission under copyright
law.
A "Modified Version" of the Document means any work containing the
Document or a portion of it, either copied verbatim, or with
modifications and/or translated into another language.
A "Secondary Section" is a named appendix or a front-matter section of
the Document that deals exclusively with the relationship of the
publishers or authors of the Document to the Document's overall
subject (or to related matters) and contains nothing that could fall
directly within that overall subject. (Thus, if the Document is in
part a textbook of mathematics, a Secondary Section may not explain
any mathematics.) The relationship could be a matter of historical
connection with the subject or with related matters, or of legal,
commercial, philosophical, ethical or political position regarding
them.
The "Invariant Sections" are certain Secondary Sections whose titles
249
License
are designated, as being those of Invariant Sections, in the notice
that says that the Document is released under this License. If a
section does not fit the above definition of Secondary then it is not
allowed to be designated as Invariant. The Document may contain zero
Invariant Sections. If the Document does not identify any Invariant
Sections then there are none.
The "Cover Texts" are certain short passages of text that are listed,
as Front-Cover Texts or Back-Cover Texts, in the notice that says that
the Document is released under this License. A Front-Cover Text may be
at most 5 words, and a Back-Cover Text may be at most 25 words.
A "Transparent" copy of the Document means a machine-readable copy,
represented in a format whose specification is available to the
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straightforwardly with generic text editors or (for images composed of
pixels) generic paint programs or (for drawings) some widely available
drawing editor, and that is suitable for input to text formatters or
for automatic translation to a variety of formats suitable for input
to text formatters. A copy made in an otherwise Transparent file
format whose markup, or absence of markup, has been arranged to thwart
or discourage subsequent modification by readers is not Transparent.
An image format is not Transparent if used for any substantial amount
of text. A copy that is not "Transparent" is called "Opaque".
Examples of suitable formats for Transparent copies include plain
ASCII without markup, Texinfo input format, LaTeX input format, SGML
or XML using a publicly available DTD, and standard-conforming simple
HTML, PostScript or PDF designed for human modification. Examples of
transparent image formats include PNG, XCF and JPG. Opaque formats
include proprietary formats that can be read and edited only by
proprietary word processors, SGML or XML for which the DTD and/or
processing tools are not generally available, and the
machine-generated HTML, PostScript or PDF produced by some word
processors for output purposes only.
The "Title Page" means, for a printed book, the title page itself,
plus such following pages as are needed to hold, legibly, the material
this License requires to appear in the title page. For works in
formats which do not have any title page as such, "Title Page" means
the text near the most prominent appearance of the work's title,
preceding the beginning of the body of the text.
The "publisher" means any person or entity that distributes copies of
the Document to the public.
A section "Entitled XYZ" means a named subunit of the Document whose
title either is precisely XYZ or contains XYZ in parentheses following
text that translates XYZ in another language. (Here XYZ stands for a
specific section name mentioned below, such as "Acknowledgements",
"Dedications", "Endorsements", or "History".) To "Preserve the Title"
of such a section when you modify the Document means that it remains a
section "Entitled XYZ" according to this definition.
The Document may include Warranty Disclaimers next to the notice which
states that this License applies to the Document. These Warranty
Disclaimers are considered to be included by reference in this
License, but only as regards disclaiming warranties: any other
implication that these Warranty Disclaimers may have is void and has
no effect on the meaning of this License.
2. VERBATIM COPYING
You may copy and distribute the Document in any medium, either
250
License
commercially or noncommercially, provided that this License, the
copyright notices, and the license notice saying this License applies
to the Document are reproduced in all copies, and that you add no
other conditions whatsoever to those of this License. You may not use
technical measures to obstruct or control the reading or further
copying of the copies you make or distribute. However, you may accept
compensation in exchange for copies. If you distribute a large enough
number of copies you must also follow the conditions in section 3.
You may also lend copies, under the same conditions stated above, and
you may publicly display copies.
3. COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly have
printed covers) of the Document, numbering more than 100, and the
Document's license notice requires Cover Texts, you must enclose the
copies in covers that carry, clearly and legibly, all these Cover
Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on
the back cover. Both covers must also clearly and legibly identify you
as the publisher of these copies. The front cover must present the
full title with all words of the title equally prominent and visible.
You may add other material on the covers in addition. Copying with
changes limited to the covers, as long as they preserve the title of
the Document and satisfy these conditions, can be treated as verbatim
copying in other respects.
If the required texts for either cover are too voluminous to fit
legibly, you should put the first ones listed (as many as fit
reasonably) on the actual cover, and continue the rest onto adjacent
pages.
If you publish or distribute Opaque copies of the Document numbering
more than 100, you must either include a machine-readable Transparent
copy along with each Opaque copy, or state in or with each Opaque copy
a computer-network location from which the general network-using
public has access to download using public-standard network protocols
a complete Transparent copy of the Document, free of added material.
If you use the latter option, you must take reasonably prudent steps,
when you begin distribution of Opaque copies in quantity, to ensure
that this Transparent copy will remain thus accessible at the stated
location until at least one year after the last time you distribute an
Opaque copy (directly or through your agents or retailers) of that
edition to the public.
It is requested, but not required, that you contact the authors of the
Document well before redistributing any large number of copies, to
give them a chance to provide you with an updated version of the
Document.
4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document under
the conditions of sections 2 and 3 above, provided that you release
the Modified Version under precisely this License, with the Modified
Version filling the role of the Document, thus licensing distribution
and modification of the Modified Version to whoever possesses a copy
of it. In addition, you must do these things in the Modified Version:
* A. Use in the Title Page (and on the covers, if any) a title
distinct from that of the Document, and from those of previous
versions (which should, if there were any, be listed in the History
section of the Document). You may use the same title as a previous
version if the original publisher of that version gives permission.
251
License
* B. List on the Title Page, as authors, one or more persons or
entities responsible for authorship of the modifications in the
Modified Version, together with at least five of the principal authors
of the Document (all of its principal authors, if it has fewer than
five), unless they release you from this requirement.
* C. State on the Title page the name of the publisher of the
Modified Version, as the publisher.
* D. Preserve all the copyright notices of the Document.
* E. Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.
* F. Include, immediately after the copyright notices, a license
notice giving the public permission to use the Modified Version under
the terms of this License, in the form shown in the Addendum below.
* G. Preserve in that license notice the full lists of Invariant
Sections and required Cover Texts given in the Document's license
notice.
* H. Include an unaltered copy of this License.
* I. Preserve the section Entitled "History", Preserve its Title,
and add to it an item stating at least the title, year, new authors,
and publisher of the Modified Version as given on the Title Page. If
there is no section Entitled "History" in the Document, create one
stating the title, year, authors, and publisher of the Document as
given on its Title Page, then add an item describing the Modified
Version as stated in the previous sentence.
* J. Preserve the network location, if any, given in the Document
for public access to a Transparent copy of the Document, and likewise
the network locations given in the Document for previous versions it
was based on. These may be placed in the "History" section. You may
omit a network location for a work that was published at least four
years before the Document itself, or if the original publisher of the
version it refers to gives permission.
* K. For any section Entitled "Acknowledgements" or "Dedications",
Preserve the Title of the section, and preserve in the section all the
substance and tone of each of the contributor acknowledgements and/or
dedications given therein.
* L. Preserve all the Invariant Sections of the Document,
unaltered in their text and in their titles. Section numbers or the
equivalent are not considered part of the section titles.
* M. Delete any section Entitled "Endorsements". Such a section
may not be included in the Modified Version.
* N. Do not retitle any existing section to be Entitled
"Endorsements" or to conflict in title with any Invariant Section.
* O. Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or
appendices that qualify as Secondary Sections and contain no material
copied from the Document, you may at your option designate some or all
of these sections as invariant. To do this, add their titles to the
list of Invariant Sections in the Modified Version's license notice.
These titles must be distinct from any other section titles.
You may add a section Entitled "Endorsements", provided it contains
nothing but endorsements of your Modified Version by various
parties—for example, statements of peer review or that the text has
been approved by an organization as the authoritative definition of a
standard.
You may add a passage of up to five words as a Front-Cover Text, and a
passage of up to 25 words as a Back-Cover Text, to the end of the list
of Cover Texts in the Modified Version. Only one passage of
Front-Cover Text and one of Back-Cover Text may be added by (or
through arrangements made by) any one entity. If the Document already
includes a cover text for the same cover, previously added by you or
by arrangement made by the same entity you are acting on behalf of,
252
License
you may not add another; but you may replace the old one, on explicit
permission from the previous publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this License
give permission to use their names for publicity for or to assert or
imply endorsement of any Modified Version.
5. COMBINING DOCUMENTS
You may combine the Document with other documents released under this
License, under the terms defined in section 4 above for modified
versions, provided that you include in the combination all of the
Invariant Sections of all of the original documents, unmodified, and
list them all as Invariant Sections of your combined work in its
license notice, and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and
multiple identical Invariant Sections may be replaced with a single
copy. If there are multiple Invariant Sections with the same name but
different contents, make the title of each such section unique by
adding at the end of it, in parentheses, the name of the original
author or publisher of that section if known, or else a unique number.
Make the same adjustment to the section titles in the list of
Invariant Sections in the license notice of the combined work.
In the combination, you must combine any sections Entitled "History"
in the various original documents, forming one section Entitled
"History"; likewise combine any sections Entitled "Acknowledgements",
and any sections Entitled "Dedications". You must delete all sections
Entitled "Endorsements".
6. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other
documents released under this License, and replace the individual
copies of this License in the various documents with a single copy
that is included in the collection, provided that you follow the rules
of this License for verbatim copying of each of the documents in all
other respects.
You may extract a single document from such a collection, and
distribute it individually under this License, provided you insert a
copy of this License into the extracted document, and follow this
License in all other respects regarding verbatim copying of that
document.
7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other separate
and independent documents or works, in or on a volume of a storage or
distribution medium, is called an "aggregate" if the copyright
resulting from the compilation is not used to limit the legal rights
of the compilation's users beyond what the individual works permit.
When the Document is included in an aggregate, this License does not
apply to the other works in the aggregate which are not themselves
derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these
copies of the Document, then if the Document is less than one half of
the entire aggregate, the Document's Cover Texts may be placed on
covers that bracket the Document within the aggregate, or the
electronic equivalent of covers if the Document is in electronic form.
Otherwise they must appear on printed covers that bracket the whole
aggregate.
253
License
8. TRANSLATION
Translation is considered a kind of modification, so you may
distribute translations of the Document under the terms of section 4.
Replacing Invariant Sections with translations requires special
permission from their copyright holders, but you may include
translations of some or all Invariant Sections in addition to the
original versions of these Invariant Sections. You may include a
translation of this License, and all the license notices in the
Document, and any Warranty Disclaimers, provided that you also include
the original English version of this License and the original versions
of those notices and disclaimers. In case of a disagreement between
the translation and the original version of this License or a notice
or disclaimer, the original version will prevail.
If a section in the Document is Entitled "Acknowledgements",
"Dedications", or "History", the requirement (section 4) to Preserve
its Title (section 1) will typically require changing the actual
title.
9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document
except as expressly provided under this License. Any attempt otherwise
to copy, modify, sublicense, or distribute it is void, and will
automatically terminate your rights under this License.
However, if you cease all violation of this License, then your license
from a particular copyright holder is reinstated (a) provisionally,
unless and until the copyright holder explicitly and finally
terminates your license, and (b) permanently, if the copyright holder
fails to notify you of the violation by some reasonable means prior to
60 days after the cessation.
Moreover, your license from a particular copyright holder is
reinstated permanently if the copyright holder notifies you of the
violation by some reasonable means, this is the first time you have
received notice of violation of this License (for any work) from that
copyright holder, and you cure the violation prior to 30 days after
your receipt of the notice.
Termination of your rights under this section does not terminate the
licenses of parties who have received copies or rights from you under
this License. If your rights have been terminated and not permanently
reinstated, receipt of a copy of some or all of the same material does
not give you any rights to use it.
10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of the
GNU Free Documentation License from time to time. Such new versions
will be similar in spirit to the present version, but may differ in
detail to address new problems or concerns. See
http://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number.
If the Document specifies that a particular numbered version of this
License "or any later version" applies to it, you have the option of
following the terms and conditions either of that specified version or
of any later version that has been published (not as a draft) by the
Free Software Foundation. If the Document does not specify a version
number of this License, you may choose any version ever published (not
as a draft) by the Free Software Foundation. If the Document specifies
254
License
that a proxy can decide which future versions of this License can be
used, that proxy's public statement of acceptance of a version
permanently authorizes you to choose that version for the Document.
11. RELICENSING
"Massive Multiauthor Collaboration Site" (or "MMC Site") means any
World Wide Web server that publishes copyrightable works and also
provides prominent facilities for anybody to edit those works. A
public wiki that anybody can edit is an example of such a server. A
"Massive Multiauthor Collaboration" (or "MMC") contained in the site
means any set of copyrightable works thus published on the MMC site.
"CC-BY-SA" means the Creative Commons Attribution-Share Alike 3.0
license published by Creative Commons Corporation, a not-for-profit
corporation with a principal place of business in San Francisco,
California, as well as future copyleft versions of that license
published by that same organization.
"Incorporate" means to publish or republish a Document, in whole or in
part, as part of another Document.
An MMC is "eligible for relicensing" if it is licensed under this
License, and if all works that were first published under this License
somewhere other than this MMC, and subsequently incorporated in whole
or in part into the MMC, (1) had no cover texts or invariant sections,
and (2) were thus incorporated prior to November 1, 2008.
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.
255
CIFS, 143
Index CNAME (DNS record), 67
context type(selinux), 215
create(mysql), 47, 49, 55
Symbols create mask (Samba), 182
/etc/apache2, 10
/etc/bind/named.conf.local, 76
/etc/group, 45
D
/etc/httpd, 10 delete(mysql), 54
/etc/inetd.conf, 152 deny hosts (Samba), 182
/etc/init.d/samba, 141 describe(mysql), 50
/etc/init.d/smb, 141 dhclient, 118
/etc/init.d/winbind, 142 dhcp server, 62
/etc/nsswitch.conf, 190, 192 directory mask (Samba), 182
/etc/passwd, 45, 199 directory security mask(samba), 183
/etc/resolv.conf, 62 DNAT, 115
/etc/samba/passdb.tdb, 198 dns, 60, 60
/etc/samba/smb.conf, 146, 147, 148, 164, 188 dnsdomainname, 66
/etc/samba/smbpasswd, 169, 196 dns namespace, 63
/etc/selinux/config, 212 dns server, 62
/etc/squid/squid.conf, 34 domain (dns), 64
/etc/sysctl.conf, 116 domain name system, 60, 60
/etc/xinetd.d/swat, 152 dpkg, 138
/proc/sys/net/ipv4/ip_forward, 116 dpkg(1), 44
/selinux, 214 drop(mysql), 48, 50, 56
/selinux/enforce, 214
/var/log/audit/audit.log, 210 F
/var/log/squid, 39 filter table (iptables), 123
.htaccess, 27 firewall, 114
.htpasswd, 17, 24 force create mode(samba), 183
.my.cnf, 46 force directory mode(samba), 183
force directory security mode(samba), 183
A force group(samba), 170
A (DNS record), 67 force security mode(samba), 183
AAAA (DNS record), 67 force user(samba), 170
allow hosts (Samba), 181 forwarder (dns), 70
apache2, 6 forward lookup query, 61
aptitude, 138, 139, 227 fqdn, 66
aptitude(8), 44 fully qualified domain name, 66
auditd, 210
authoritative (dns), 71 G
authoritative zone, 66 getenforce, 211
axfr, 74 getent(1), 191
getfattr(1), 217
B git, 226
bind, 64 github, 232
bind(DNS), 90 glue record (dns), 67
browsable (Samba), 182 grant(mysql), 48
browseable (Samba), 182 group by(mysql), 54
browser master, 196 guest ok (Samba), 157
C H
cahing only name server, 68 hide unreadable (Samba), 182
chain (iptables), 123 host (DNS record), 67
char(mysql), 49 hostname, 66, 143
chcon(1), 216, 217 hosts.txt, 60
chkconfig, 210 hosts allow (Samba), 181
chmod, 213 hosts deny (Samba), 182
256
Index
htpasswd(1), 17, 24 packet forwarding, 114
httpd, 7 passdb backend (Samba), 170
PAT, 115
I Paul Mockapetris, 60
IBM, 143 php, 43
id(1), 216 ping, 117, 118
identity(selinux), 214 port forwarding, 115
idmap gid(samba), 188 primary dns server, 71
idmap uid(samba), 188 primary server (DNS), 73
inetd(8), 152 proxy server, 33
insert(mysql), 51 ps(1), 217
integer(mysql), 49 PTR (DNS record), 67
invalid users (Samba), 181 public key, 232
iptables, 122, 123
iptables save, 127 Q
iterative query, 70 query (dns), 61
ixfr, 74
R
L read list (Samba), 181
LAMP, 43 read only (Samba), 164
ls, 213 recursive query, 70
ls(1), 217 reverse lookup query, 61
roaming profiles(samba), 200
M role(selinux), 214
mac address, 117 root(DNS), 63
mangle table (iptables), 123 root(mysql), 44
masquerading, 115 root hints, 64
master server (DNS), 73 root server (dns), 69
MX (DNS record), 67 root servers (dns), 63
mysql, 43, 45, 46, 47 router, 114
mysql(group), 45 rpm, 138
mysql(user), 45 rpm(1), 44
mysql-client, 44 rpm(8), 139
mysqld, 45
mysql-server, 44
S
samba, 138
N secondary dns server, 71
NAPT, 115 secondary server (DNS), 73
NAT, 115 security(Samba), 157
nat table (iptables), 123 security mask(samba), 183
NetBIOS names, 143 security mode(samba), 174
netcat, 160 select(mysql), 51, 52, 52
net groupmap, 201 SELinux, 209
net rpc join(samba), 189 selinux, 212
net use(microsoft), 159, 164, 175 selinux-activate, 210
net view(microsoft), 146, 151 service(8), 141
nmbd(8), 142 sestatus, 212
NS (DNS record), 67 setenforce, 211
nslookup, 61 show(mysql), 47, 49
NT_STATUS_BAD_NETWORK_NAME, 176 slave server (DNS), 73
NT_STATUS_LOGON_FAILURE, 176 SMB, 143
smbclient, 149, 158
O smbclient(1), 148, 175
order by(mysql), 53 smbd(8), 142, 146, 169
smbpasswd(1), 201
P smbpasswd(8), 169, 174
packet filtering, 114, 124 smbtree, 151
257
Index
smbtree(1), 150
smtp, 67
SNAT, 115
soa (dns record), 71
SQL, 43, 51
squid, 33
stateful firewall, 114
swat(8), 152
sysctl, 116
T
tcpdump, 61, 118
tdbsam, 170, 196, 198
testparm(1), 147, 147, 148
tld, 65
TLD (dns), 65
top level domain, 65
transition(selinux), 216
trigger(mysql), 55
triggers(mysql), 44
type(selinux), 215
U
update(mysql), 52
use(mysql), 48
V
valid users (Samba), 181
varchar(mysql), 49
virtualbox, 117
vmware, 117
W
wbinfo(1), 190, 191
webalizer, 27
winbind(8), 190
winbind(samba), 188
winbindd(8), 142, 142, 190
wireshark, 118
workgroup, 157
writable (Samba), 164
write list (Samba), 181
X
xinetd(8), 152
Y
yum, 139
Z
zone (dns), 66, 71
zone transfer (dns), 71
258