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tools to make chroot jails easily


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:

[jk_lsh] comment = Jailkit limited shell paths = /usr/sbin/jk_lsh, /etc/jailkit/jk_lsh.ini users = root groups = root need_logsocket = 1 includesections = uidbasics
[sftp] 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.


-f --force Force overwriting of existing files
-v --verbose
Will give verbose output
-k --hardlink
Try to create hardlinks instead of copying the files
-c configfile --configfile=configfile
Use alternative configfile
-l --list List available sections in the config file
-j --jail <jail>
Specify the jail directory to operate on.
-h --help The help screen




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.
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