> For the complete documentation index, see [llms.txt](https://book.bsdcn.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://book.bsdcn.org/ask/flat/chapter-33-linux-jails/di-33.3-jie-ubuntu-jail.md).

# 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:

```sh
# 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:

```ini
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:

```ini
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:

```sh
# pfctl -t jails -T add 192.168.5.2
```

## Start the Ubuntu Jail Instance

Start the instance:

```sh
# jail -c ubuntu
```

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

```sh
# 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:

```sh
# 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.


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