Jailmaker

Persistent Linux 'jails' on TrueNAS SCALE to install software (docker-compose, portainer, podman, etc.) with full access to all files via bind mounts.

Disclaimer

USING THIS SCRIPT IS AT YOUR OWN RISK! IT COMES WITHOUT WARRANTY AND IS NOT SUPPORTED BY IXSYSTEMS.

Summary

TrueNAS SCALE can create persistent Linux 'jails' with systemd-nspawn. This script helps with the following:

• Installing the systemd-container package (which includes systemd-nspawn)
• Setting up the jail so it won't be lost when you update SCALE
• Choosing a distro (Debian 12 strongly recommended, but Ubuntu, Arch Linux or Rocky Linux seem good choices too)
• Optional: configuring the jail so you can run Docker inside it
• Optional: GPU passthrough (including nvidia GPU with the drivers bind mounted from the host)
• Starting the jail with your config applied

Installation

Create a new dataset called jailmaker with the default settings (from TrueNAS web interface). Then login as the root user and download jlmkr.py.

cd /mnt/mypool/jailmaker
curl --location --remote-name https://raw.githubusercontent.com/Jip-Hop/jailmaker/main/jlmkr.py
chmod +x jlmkr.py
./jlmkr.py install

The jlmkr.py script (and the jails + config it creates) are now stored on the jailmaker dataset and will survive updates of TrueNAS SCALE. Additionally a symlink has been created so you can call jlmkr from anywhere.

After an update of TrueNAS SCALE the symlink will be lost and systemd-nspawn (the core package which makes jailmaker work) may be gone too. Not to worry, just run ./jlmkr.py install again or use the ./jlmkr.py startup command.

Usage

Create Jail

Creating a jail is interactive. You'll be presented with questions which guide you through the process.

jlmkr create myjail

After answering a few questions you should have your first jail up and running!

Startup Jails on Boot

# Best to call startup directly (not through the jlmkr symlink)
/mnt/mypool/jailmaker/jlmkr.py startup

# Can be called from the symlink too...
# But this may not be available after a TrueNAS SCALE update
jlmkr startup

In order to start jails automatically after TrueNAS boots, run /mnt/mypool/jailmaker/jlmkr.py startup as Post Init Script with Type Command from the TrueNAS web interface. This will automatically fix the installation of systemd-nspawn and setup the jlmkr symlink, as well as start all the jails with startup=1 in the config file. Running the startup command Post Init is recommended to keep jailmaker working after a TrueNAS SCALE update.

Start Jail

jlmkr start myjail

List Jails

jlmkr list

Execute Command in Jail

You may want to execute a command inside a jail, for example from a shell script or a CRON job. The example below executes the env command inside the jail.

jlmkr exec myjail env

This example executes bash inside the jail with a command as additional argument.

jlmkr exec myjail bash -c 'echo test; echo $RANDOM;'

Edit Jail Config

jlmkr edit myjail

Once you've created a jail, it will exist in a directory inside the jails dir next to jlmkr.py. For example /mnt/mypool/jailmaker/jails/myjail if you've named your jail myjail. You may edit the jail configuration file, e.g. using the jlmkr edit myjail command (which uses the nano text editor). You'll have to stop the jail and start it again with jlmkr for these changes to take effect.

Remove Jail

jlmkr remove myjail

Stop Jail

jlmkr stop myjail

Jail Shell

jlmkr shell myjail

Jail Status

jlmkr status myjail

Jail Logs

jlmkr log myjail

Additional Commands

Expert users may use the following additional commands to manage jails directly: machinectl, systemd-nspawn, systemd-run, systemctl and journalctl. The jlmkr script uses these commands under the hood and implements a subset of their capabilities. If you use them directly you will bypass any safety checks or configuration done by jlmkr and not everything will work in the context of TrueNAS SCALE.

Networking

By default the jail will have full access to the host network. No further setup is required. You may download and install additional packages inside the jail. Note that some ports are already occupied by TrueNAS SCALE (e.g. 443 for the web interface), so your jail can't listen on these ports. This is inconvenient if you want to host some services (e.g. traefik) inside the jail. To workaround this issue when using host networking, you may disable DHCP and add several static IP addresses (Aliases) through the TrueNAS web interface. If you setup the TrueNAS web interface to only listen on one of these IP addresses, the ports on the remaining IP addresses remain available for the jail to listen on.

See Advanced Networking for more.

Docker

The jailmaker script won't install Docker for you, but it can setup the jail with the capabilities required to run docker. You can manually install Docker inside the jail using the official installation guide or use convenience script.

Nvidia GPU

To make passthrough of the nvidia GPU work, you need to schedule a Pre Init command. The reason is that TrueNAS SCALE by default doesn't load the nvidia kernel modules (and jailmaker doesn't do that either). This screenshot shows what the configuration should look like.

[ ! -f /dev/nvidia-uvm ] && modprobe nvidia-current-uvm && /usr/bin/nvidia-modprobe -c0 -u

Documentation

Additional documentation contributed by the community can be found in the docs directory.

Comparison

TODO: write comparison between systemd-nspawn (without jailmaker), LXC, VMs, Docker (on the host).

Incompatible Distros

The rootfs image jlmkr.py downloads comes from the Linux Containers Image server. These images are made for LXC. We can use them with systemd-nspawn too, although not all of them work properly. For example, the alpine image doesn't work well. If you stick with common systemd based distros (Debian, Ubuntu, Arch Linux...) you should be fine.

Tips & Tricks

Colorized bash prompt

To visually distinguish between a root shell inside the jail and a root shell outside the jail, it's possible to colorize the shell prompt. When using a debian jail with the bash shell, you may run the following command to get a yellow prompt inside the jail (will be activated the next time you run jlmkr shell myjail):

echo "PS1='${debian_chroot:+($debian_chroot)}\[\033[01;33m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '" >> ~/.bashrc

References

• TrueNAS Forum Thread about Jailmaker
• systemd-nspawn
• machinectl
• systemd-run
• Run docker in systemd-nspawn
• The original Jailmaker gist