DOKK / manpages / debian 12 / jailkit / jk_init.8.en
jk_init(8) jk_init jk_init(8)

jk_init - a utility to quicky create functional jail directories

jk_init -j jail section

jk_init -v -f -k -j jail section

It is not an easy task to setup a jail (a changed root) in a functional way. If you want the user to be able to run cvs for example, it will not work to simply copy the cvs binary into the users jail. You will find that cvs needs libraries as well. cvs also needs the /dev/null device. Finally you need something to start cvs: you need a shell too. And the shell might need files like /etc/passwd and /etc/nsswitch.conf.

With jk_init you can automate these tasks. You can create a section in the configfile /etc/jailkit/jk_init.ini that has all the files, directories and devices, and you can use jk_init to setup such a jail with a single command. The default configfile has examples for cvs, sftp, scp, rsync and more for Debian and Ubuntu Linux. For other operating systems the defaults might need some (minor) updates.

An example configfile section might look like this:

comment = Jailkit limited shell
paths = /usr/sbin/jk_lsh, /etc/jailkit/jk_lsh.ini
users = root
groups = root
need_logsocket = 1
includesections = uidbasics
comment = ssh secure ftp with Jailkit limited shell
paths = /usr/lib/sftp-server
includesections = netbasics, uidbasics
devices = /dev/urandom, /dev/null
emptydirs = /svr

The comment entry specifies the comment that is shown if jk_init option -l or --list is used. The paths entry specifies which files and directories need to be copied into the jail. Executables and libraries are checked for any required libraries, and these requirements are copied too. All files are created with user root as owner. The paths_w_owner entry specifies which paths need to be copied with their current ownership. This can be used to copy files that need to be writable by a server process that does not run as user root (for example database files). The users and groups entries specify which users and groups that need to be present in <jail>/etc/passwd. If the need_logsocket entry is set to "1" the jk_socketd.ini file is modified to include a /dev/log socket in this jail. The devices entry specifies which devices are required in the jail. The includesections entry specifies which other sections need to be processed as well when processing the current section. In the above example, the jk_lsh section is automatically included if the sftp section is processed. Finally the emptydirs entry specifies which directories to create as empty directories. This can be useful to create for example mountpoints in the jail.

The entries executables , regularfiles , directories and libraries are all replaced by the entry paths. They are still supported, but are handled similar to the paths entry.

Many unix like operating systems install files in different locations. The default jk_init config file has defaults taken from Debian and Ubuntu. The default config file may not work on other platforms. You probably need to customise jk_init.ini for your platform and your applications.

Force overwriting of existing files
Will give verbose output
Try to create hardlinks instead of copying the files
Use alternative configfile
List available sections in the config file
Specify the jail directory to operate on.
The help screen


jailkit(8) jk_check(8) jk_chrootlaunch(8) jk_chrootsh(8) jk_cp(8) jk_jailuser(8) jk_list(8) jk_lsh(8) jk_procmailwrapper(8) jk_socketd(8) jk_uchroot(8) jk_update(8) chroot(2) ldd(1) mknod(1) ln(1) chmod(1) mkdir(1)

Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Olivier Sessink

Copying and distribution of this file, with or without modification, are permitted in any medium without royalty provided the copyright notice and this notice are preserved.

07-02-2010 JAILKIT