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"THE BEER-WARE LICENSE" (Revision 42):
<phk@FreeBSD.ORG> wrote this file. As long as you retain this notice you
can do whatever you want with this stuff. If we meet some day, and you think
this stuff is worth it, you can buy me a beer in return. Poul-Henning Kamp
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$FreeBSD: head/usr.sbin/jail/jail.8 57180 2000-02-13 05:15:29Z chris $
.Dd April 28, 1999 .Dt JAIL 8 .Os FreeBSD 4.0 .Sh NAME .Nm jail .Nd imprison process and its descendants .Sh SYNOPSIS .Nm jail .Ar path .Ar hostname .Ar ip-number .Ar command .Ar ... .Sh DESCRIPTION The .Nm command imprisons a process and all future decendants.
p Please see the .Xr jail 2 man page for further details. .Sh EXAMPLES .Ss Setting up a Jail Directory Tree This shows how to setup a jail directory tree: d -literal D=/here/is/the/jail cd /usr/src make hierarchy DESTDIR=$D make obj make all make install DESTDIR=$D cd etc make distribution DESTDIR=$D NO_MAKEDEV=yes cd $D/dev sh MAKEDEV jail cd $D ln -sf dev/null kernel .Ed .Ss Setting Up a Jail Do what was described in .Sx Setting Up a Jail Directory Tree to build the jail directory tree. For the sake of this example, we will assume you built it in
a /data/jail/192.168.11.100 , named for the jailed IP address. Substitute below as needed with your own directory, IP address, and hostname.
p First, you will want to set up your real system's environment to be .Dq jail-friendly. For consistency, we will refer to the parent box as the .Dq host environment, and to the jailed virtual machine as the .Dq jail environment. Because jail is implemented using IP aliases, one of the first things to do is to disable IP services on the host system that listen on all local IP addresses for a service. This means changing inetd to only listen on the appropriate IP address, and so forth. Add the following to
a /etc/rc.conf in the host environment: d -literal -offset indent sendmail_enable="NO" inetd_flas="-wW -a 192.168.11.23" portmap_enable="NO" .Ed
p .Li 192.169.11.23 is the native IP address for the host system, in this case. It is possible to set up jails without using an exposed host IP, but in most virtual hosting environments, you won't want to do this. Sendmail can be configured to listen to a specific IP, but this involves modifying
a /etc/sendmail.cf , so it's easier to just disable it, and only have mail service within jails. This is also more secure. You will probably also want to disable the portmapper. You can reboot to let this take effect, or manually kill/restart the daemons.
p Start your jail for the first time without configuring the network interface so that you can clean it up a little and set up accounts. As with any machine (virtual or not) you will need to set a root password, time zone, etc. Before beginning, you may want to copy .Xr sysinstall 8 into the tree so that you can use it to set things up easily. Do this using: d -literal -offset indent # mkdir /data/jail/192.168.11.100/stand # cp /stand/sysinstall /data/jail/192.168.11.100/stand .Ed
p Now start the jail: d -literal -offset indent # jail /data/jail/192.168.11.100 testhostname 192.168.11.100 /bin/sh .Ed
p You will end up with a shell prompt, assuming no errors, within the jail. You can now run
a /stand/sysinstall and do the post-install configuration to set various configuration options, including:
p l -bullet -offset indent -compact t Disable the port mapper t Set a root password, probably different from the real host system t Set the timezone t Add accounts for users in the jail environment t Install any packages that you think the environment requires .El
p Outside of .Xr sysinstall 8 , you will probably also want to configure .Xr resolv.conf 5 appropriately, as well as any package-specific configuration, such as Web servers, ssh, etc. You'll probably want to replace the .Dq /dev/console line of
a /etc/syslog.conf with something more useful, such as UDP-based logging to a log host, or even the host environment's syslog.
p Exit from the shell, and the jail will be shut down. .Ss Starting the Jail You are now ready to restart the jail and bring up the environment with all of its daemons and other programs. To do this, first bring up the virtual host interface, and then start the jail's
a /etc/rc script from within the jail. d -literal -offset indent # ifconfig ed0 inet alias 192.168.11.100 netmask 255.255.255.255 # mount -t procfs proc /data/jail/192.168.11.100/proc # jail /data/jail/192.168.11.100 testhostname 192.168.11.100 \\ /bin/sh /etc/rc .Ed
p A few warnings will be produced, because most .Xr sysctl 8 configuration variables cannot be set from within the jail, as they are global across all jails and the host environment. However, it should all work properly. You should be able to see .Xr inetd 8 , .Xr syslogd 8 , and other processes running within the jail using .Xr ps 1 , with the .Dq J flag appearing beside jailed processes. You should also be able to telnet to the hostname or IP address of the jailed environment, and log in using the acounts you created previously. .Ss Managing the jail Normal machine shutdown commands, such as .Xr halt 8 , .Xr reboot 8 , and .Xr shutdown 8 , cannot be used successfully within the jail. To kill all processes in a jail, you may log into the jail and, as root, use one of the following commands, depending on what you want to accomplish:
p l -bullet -offset indent -compact t .Li kill -TERM -1 t .Li kill -KILL -1 .El
p This will send the .Dq TERM or .Dq KILL signals to all processes in the jail from within the jail. Depending on the intended use of the jail, you may also want to run
a /etc/rc.shutdown from within the jail. Currently there is no way to insert new processes into a jail, so you must first log into the jail before performing these actions.
p To kill processes from outside the jail, you must individually identify the PID of each process to be killed. The
a /proc/ Ns Va pid Ns Pa /status file contains, as its last field, the hostname of the jail in which the process runs, or .Dq - to indicate that the process is not running within a jail. The .Xr ps 1 command also shows a .Dq J flag for processes in a jail. However, the hostname for a jail may be, by default, modified from within the jail, so the
a /proc status entry is unreliably by default. To disable the setting of the hostname from within a jail, set the .Dq Va kern.jail.set_hostname_allowed sysctl variable in the host environment to 0, which will affect all jails. In a future version of FreeBSD, the mechanisms for managing jails will be more refined. .Sh SEE ALSO .Xr chroot 2 , .Xr jail 2 .Sh HISTORY The .Fn jail function call appeared in .Fx 4.0 . .Sh AUTHORS The jail feature was written by Poul-Henning Kamp for R&D Associates .Dq Li http://www.rndassociates.com/ who contributed it to FreeBSD.