Unfortunately since version 22.12.3 TrueNAS SCALE no longer includes systemd-nspawn. In order to use jailmaker, we need to first install systemd-nspawn using the command below.
```shell
./jlmkr.py install
```
We need to do this again after each update of TrueNAS SCALE. So it is recommended to schedule this command as Post Init Script (see [Autostart Jail on Boot](#autostart-jail-on-boot)).
Additionally the install command will create a symlink from `/usr/local/sbin/jlmkr` to `jlmkr.py`. Thanks this this you can now run the `jlmkr` command from anywhere (instead of having to run `./jlmkr.py` from inside the directory where you've placed it).
In order to start a jail automatically after TrueNAS boots, run `jlmkr start myjail` as Post Init Script with Type `Command` from the TrueNAS web interface. If you want to automatically install systemd-nspawn if it's not already installed (recommended to keep working after a TrueNAS SCALE update) then you may use a command such as this instead: `/mnt/mypool/jailmaker/jlmkr.py install && jlmkr start 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.
If you want to run a command inside a jail, for example from a shell script or a CRON job, you may use `systemd-run` with the `--machine` flag. The example below runs the `env` command inside the jail.
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](./NETWORKING.md) for more.
Jailmaker 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](https://docs.docker.com/engine/install/#server) or use [convenience script](https://get.docker.com).
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](https://user-images.githubusercontent.com/1704047/222915803-d6dd51b0-c4dd-4189-84be-a04d38cca0b3.png) shows what the configuration should look like.
The rootfs image `jlmkr.py` downloads comes from the [Linux Containers Image server](https://images.linuxcontainers.org). 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.
