33.3 Ubuntu Jail

The method for creating an Ubuntu Jail is the same as for Debian. This example uses Ubuntu 22.04 (Jammy).

Build the Base System

Create the Ubuntu Jail root directory and install the system using debootstrap:

# Create the Ubuntu Jail root directory
# mkdir -p /usr/jails/ubuntu

# Install Ubuntu Jammy system into the Jail using debootstrap, specifying the mirror
# debootstrap jammy /usr/jails/ubuntu https://mirrors.ustc.edu.cn/ubuntu/

Manage Mount Files

Create the /etc/fstab.ubuntu file with the following content:

devfs      /usr/jails/ubuntu/dev      devfs       rw                      0  0
tmpfs      /usr/jails/ubuntu/dev/shm  tmpfs       rw,size=1g,mode=1777    0  0
fdescfs    /usr/jails/ubuntu/dev/fd   fdescfs     rw,linrdlnk             0  0
linprocfs  /usr/jails/ubuntu/proc     linprocfs   rw                      0  0
linsysfs   /usr/jails/ubuntu/sys      linsysfs    rw                      0  0
/tmp       /usr/jails/ubuntu/tmp      nullfs      rw                      0  0

Manage the Jail Configuration File

Add the Ubuntu configuration to the /etc/jail.conf file:

ubuntu {                               # Jail name
  host.hostname = "ubuntu";             # Set the Jail's hostname
  mount.fstab = "/etc/fstab.ubuntu";    # fstab file used by the Jail
  path = "/usr/jails/ubuntu";           # Jail root directory path
  devfs_ruleset = 4;                     # devfs mount ruleset
  enforce_statfs = 1;                    # Set mount point visibility
  allow.mount;                          # Allow mounting file systems
  allow.mount.devfs;                     # Allow mounting devfs
  exec.start = "/bin/true";              # Command executed at startup
  exec.stop = "/bin/true";               # Command executed at shutdown
  persist;                               # Keep the Jail alive even without processes
  allow.raw_sockets;                      # Allow raw sockets
  interface = "lo1";                      # Specify the network interface
  ip4.addr = 192.168.5.2;                 # Assign IPv4 address
  ip6 = "disable";                        # Disable IPv6
}

Allow Network Access

Add the Jail's address to the jails table in the pf firewall to allow the Jail to access the network:

# pfctl -t jails -T add 192.168.5.2

Start the Ubuntu Jail Instance

Start the instance:

# jail -c ubuntu

If jail_enable=YES has already been set in /etc/rc.conf, you can also use:

# service jail start ubuntu

For boot-time startup settings, refer to the Debian Jail. Run the following command to add the ubuntu Jail to the startup list:

# sysrc jail_list+=ubuntu

Update the Ubuntu System

The process is the same as for the Debian Jail; simply replace debian with ubuntu in the commands. Refer to other relevant chapters in this book.

References

• FreeBSD Chinese Handbook. 12.3. Linux User Space[EB/OL]. [2026-03-25]. https://handbook.bsdcn.org/di-12-zhang-linux-er-jin-zhi-jian-rong-ceng/12.3.-linux-yong-hu-kong-jian.html. A tutorial in the Chinese handbook on building a complete Linux user space environment.
• Ubuntu Documentation. Install Firefox on Linux[EB/OL]. [2026-04-17]. https://support.mozilla.org/en-US/kb/install-firefox-linux. Firefox is distributed as a snap by default in Ubuntu 22.04, but can also be installed as a deb package via PPA.