This page describes the steps required to configure an Ubuntu-based Linux jail or chroot - a complete Linux userspace environment running on top of [[Linuxulator]].

Required steps:

  - Have %%FreeBSD%% 14-CURRENT or 13.0-RELEASE on amd64, or 14-CURRENT on arm64
  - Have linux(4) compatibility enabled, as documented in the [[https://www.freebsd.org/cgi/man.cgi?linux|man page]]; this boils down to having ''%%linux_enable=YES%%'' in ''%%/etc/rc.conf%%''; running ''%%service linux start%%'' as root after adding it there.  This is to load the neccessary kernel modules and set some sysctls.
  - Install [[https://www.freshports.org/sysutils/debootstrap/|sysutils/debootstrap]]; ''%%pkg install debootstrap%%''.
  - Run ''%%debootstrap bionic /compat/ubuntu%%''.  This will install Ubuntu Bionic into ''%%/compat/ubuntu%%''.  While it is technically possible to install into ''%%/compat/linux%%'' instead, it's discouraged due to possible clash with %%CentOS%%-based ports and packages ([[https://www.freshports.org/emulators/linux_base-c7/|linux_base-c7]] et al).  You might see some errors during the configuration phase - they are generally harmless; as long as the log ends with "Base system installed successfully", everything is fine.
  - Set up mounts in ''%%/etc/fstab%%'', as described in [[https://www.freebsd.org/cgi/man.cgi?linux|linux(4) man page]].  Remember to actually mount them (''%%mount -al%%'' if you use the example below) afterwards.  If you want to share home directory contents, and be able to run X11 apps, you will also need [[https://www.freebsd.org/cgi/man.cgi?nullfs|null mounts]] for ''%%/home%%'' and ''%%/tmp%%''.  For example:

<code>
# Device        Mountpoint              FStype          Options                      Dump    Pass#
devfs           /compat/ubuntu/dev      devfs           rw,late                      0       0
tmpfs           /compat/ubuntu/dev/shm  tmpfs           rw,late,size=1g,mode=1777    0       0
fdescfs         /compat/ubuntu/dev/fd   fdescfs         rw,late,linrdlnk             0       0
linprocfs       /compat/ubuntu/proc     linprocfs       rw,late                      0       0
linsysfs        /compat/ubuntu/sys      linsysfs        rw,late                      0       0
/tmp            /compat/ubuntu/tmp      nullfs          rw,late                      0       0
/home           /compat/ubuntu/home     nullfs          rw,late                      0       0
</code>

That's it!  You should now be able to run ''%%chroot /compat/ubuntu /bin/bash%%'' and use ''%%apt%%'' like you would on a typical Ubuntu instance.  You will probably want to add users and groups with UIDs/GIDs matching the ones on the host system.  While ''%%systemd%%'' doesn't work, the ''%%service%%'' command works as usual.  Some things that would probably get set up by the installer require manual tweaking: if you get warnings about LC_ALL, you'll want to install appropriate locales (''%%apt search language-pack%%'').  There's a configuration problem with the rsyslog package; use ''%%apt remove rsyslog%%'' to make ''%%apt%%'' stop whining.  To get your environment variables set up in the typical Ubuntu way you might want to start sshd(8) (''%%service ssh start%%'') and log in this way; you can add ''%%chroot /compat/ubuntu /usr/sbin/service ssh start%%'' to ''%%/etc/rc.local%%'' to make it run at boot.  As with any other Ubuntu, you will probably want to add the package repositories missing from defaults; for the amd64 (x86_64) version of Bionic, make your ''%%/compat/ubuntu/etc/apt/sources.list%%'' look like this:

<code>
deb http://archive.ubuntu.com/ubuntu bionic main universe restricted multiverse
deb http://security.ubuntu.com/ubuntu/ bionic-security universe multiverse restricted main
deb http://archive.ubuntu.com/ubuntu bionic-backports universe multiverse restricted main
deb http://archive.ubuntu.com/ubuntu bionic-updates universe multiverse restricted main
</code>

For arm64, it should look like this:

<code>
deb http://ports.ubuntu.com/ubuntu-ports bionic main universe restricted multiverse
</code>

Note that the instructions above apply to both jails and chroots - it makes no difference from Linuxulator's point of view; the part that matters is changing the filesystem root directory, which is common to both.  Also note that the instructions don't describe how to manage the jail; take a look at [[https://www.harshadsharma.com/posts/2020/12/ubuntu-bionic-on-freebsd-with-iocage-managed-jails/|this article]] for instructions on how to manage your Ubuntu jail using [[https://iocage.io/|iocage]], or [[https://bastillebsd.org/blog/2021/08/01/bastille-experiments-with-ubuntu-and-debian-linux-containers/|this one]] for [[https://bastillebsd.org/|Bastille]].

You can find the list of tested apps at [[LinuxApps]].  Feel free to add new entries.

It is possible to use VNET with a Linux jail if one replaces the linux version of ''%%ifconfig%%'' with ''%%/rescue/ifconfig%%'' and ''%%route%%'' with ''%%/rescue/route%%'' (see the [[https://forums.freebsd.org/threads/vnet-and-a-linux-jail.82787/|forums]] for a more in-depth explanation).

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{{tag>HowTo}}