(howto-admin-systemd)=

# Customizing `systemd` services

By default, TLJH configures two `systemd` services to run JupyterHub and Traefik.

These services come with a default set of settings, which are specified in
[jupyterhub.service](https://github.com/jupyterhub/the-littlest-jupyterhub/blob/HEAD/tljh/systemd-units/jupyterhub.service) and
[traefik.service](https://github.com/jupyterhub/the-littlest-jupyterhub/blob/HEAD/tljh/systemd-units/traefik.service).
They look like the following:

```bash
[Unit]
Requires=traefik.service
After=traefik.service

[Service]
User=root
Restart=always
WorkingDirectory=/opt/tljh/state
PrivateTmp=yes
PrivateDevices=yes
ProtectKernelTunables=yes
ProtectKernelModules=yes
Environment=TLJH_INSTALL_PREFIX=/opt/tljh
ExecStart=/opt/tljh/hub/bin/python3 -m jupyterhub -f jupyterhub_config.py --upgrade-db

[Install]
WantedBy=multi-user.target
```

However in some cases, admins might want to have better control on these settings.

For example when mounting shared volumes over the network using [Samba](<https://en.wikipedia.org/wiki/Samba_(software)>),
these namespacing settings might be a bit too strict and prevent users from accessing the shared volumes.

## Overriding settings with `override.conf`

To override the `jupyterhub` settings, it is possible to provide a custom `/etc/systemd/system/jupyterhub.service.d/override.conf` file.

Here is an example for the content of the file:

```bash
[Service]
PrivateTmp=no
PrivateDevices=no
ProtectKernelTunables=no
ProtectKernelModules=no
```

This example should be useful in the case of mounting volumes using Samba and sharing them with the JupyterHub users.
You might also want to provide your own options, which are listed in the
[systemd documentation](https://www.freedesktop.org/software/systemd/man/systemd.exec.html).

Then make sure to reload the daemon and the `jupyterhub` service:

```bash
sudo systemctl daemon-reload
sudo systemctl restart jupyterhub
```

Then check the status with:

```bash
sudo systemctl status jupyterhub
```

The output should look like the following:

```{image} ../../images/admin/jupyterhub-systemd-status.png
:alt: Checking the status of the JupyterHub systemd service
```

To override the `traefik` settings, create a new file under `/etc/systemd/system/traefik.service.d/override.conf`
and follow the same steps.

## References

If you would like to learn more about the `systemd` security features, check out these references:

- [List of systemd settings](https://www.freedesktop.org/software/systemd/man/systemd.exec.html)
- [Mastering systemd: Securing and sandboxing applications and services](https://www.redhat.com/sysadmin/mastering-systemd)
