1. Paths

For system units, managed by the root user, use the directory /etc/systemd/system.

For user managed units use the directory ~/.config/systemd/user.

Units that come from installed packages normally use the directory /usr/lib/systemd/system.

2. Override an existing unit

To override existing preconfigured units use the command systemctl edit <unit> or add the file /etc/systemd/system/<unit>/override.conf with the changed options.

3. The service manager `systemctl`

User-Mode

To run the service manager (systemctl) in user-mode for user managed units in the ~/.config/systemd/user directory, add the --user parameter to every execution like this:

systemctl status --user <unit>

Reload new or changed unit files

After adding or changing a unit file reload the changes with:

systemctl daemon-reload

Frequently used Commands

Start a unit:

systemctl start <unit>

Stop a unit:

systemctl stop <unit>

Restart a unit:

systemctl restart <unit>

Asks a unit listed on the command line to reload it's configuration (for the example case of Apache, this will reload Apache's httpd.conf in the web server, not the apache.service systemd unit file):

systemctl reload <unit>

Enable a unit (add to autostart):

systemctl enable <unit>

Install a unit (create symlinks from [Install] section for auto start) and start it afterwards:

systemctl enable --now <unit>

Disable a unit (remove symlinks made with enable) and stop it afterwards:

systemctl disable --now <unit>

Display status of a unit:

systemctl restart <unit>

Mask a unit to make it impossible to start:

systemctl mask <unit>

Unmask a unit:

systemctl unmask <unit>

Undo all changes made to a unit file with edit or mask:

systemctl revert <unit>

List all timers:

systemctl list-timers [--all]

4. Show log of a unit

System units:

journalctl --unit <unit>

User units:

journalctl --user-unit <unit>

5. Usefull systemd tools

Syntax check of unit file:

systemd-analyze verify [--user] <unit>

Escape strings for usage in systemd mount unit names:

systemd-escape mnt/example

Calculate the next 10 elapses of a calendar expression for a timer:

systemd-analyze calendar --iterations=10 <expression>

6. Examples

Add a new service

Create the unit file
- Either with systemctl
```
systemctl edit --user --force --full example.service
```
- or by creating the unit file manually and then reloading the daemon
```
systemctl daemon-reload --user
```

Install the service and start it

systemctl enable --user --now example.service

Check the status to see if the service is running
```
systemctl status --user example.service
```

Remove a service

Remove all drop in files
```
systemctl revert --user example.service
```

Uninstall the service and stop it

systemctl disable --user --now example.service

Delete the unit file

rm "$(systemctl show --user -P FragmentPath test.service)"

Reload the daemon
```
systemctl daemon-reload --user
```

Reset a possible "failed" state

systemctl reset-failed --user example.service

7. Man pages

systemd.unit
systemd.mount
systemd.automount
systemd.path
systemd.service
systemd.timer

systemctl

systemd.time

systemd-analyze

ioqy/systemd-unit-example