Systemd: Service File Examples

Most Linux distributions use systemd as a system and service manager.

The systemctl is the main command in systemd, used to control services.

In this tutorial i will show how to create a systemd service file that will allow you to control your service using the systemctl command, how to restart systemd without reboot to reload unit files and how to enable your new service.

I will also show and describe the most important systemd service file options with the live examples of the systemd service files.

Create Systemd Service File

Create a systemd service file /etc/systemd/system/foo-daemon.service (replace the foo-daemon with your service name):

$ sudo touch /etc/systemd/system/foo-daemon.service
$ sudo chmod 664 /etc/systemd/system/foo-daemon.service

Open the foo-daemon.service file and add the minimal service configuration options that allow this service to be controlled via systemctl:

[Unit]
Description=Foo

[Service]
ExecStart=/usr/sbin/foo-daemon

[Install]
WantedBy=multi-user.target

Path To Daemon: If you don’t know the full path to a daemon, try which foo-daemon.

Once the service file is changed, it needs to reload systemd configuration:

$ sudo systemctl daemon-reload

Now you should be able to start, stop, restart and check the service status

$ sudo systemctl start foo-daemon
$ sudo systemctl stop foo-daemon
$ sudo systemctl restart foo-daemon
$ systemctl status foo-daemon

To configure a service to start automatically on boot, you need to enable it:

$ sudo systemctl enable foo-daemon

To check the service logs, run:

$ journalctl -u foo-daemon

Systemd Service File Options

Systemd service files typically consist of three sections.

The common configuration items are configured in the generic [Unit] and [Install] sections.

The service specific configuration options are configured in the [Service] section.

Important `[Unit]` Section Options

Option	Description
`Description`	A short description of the unit.
`Documentation`	A list of URIs referencing documentation.
`Before`, `After`	The order in which units are started.
`Requires`	If this unit gets activated, the units listed here will be activated as well. If one of the other units gets deactivated or fails, this unit will be deactivated.
`Wants`	Configures weaker dependencies than `Requires`. If any of the listed units does not start successfully, it has no impact on the unit activation. This is the recommended way to establish custom unit dependencies.
`Conflicts`	If a unit has a `Conflicts` setting on another unit, starting the former will stop the latter and vice versa.

A complete list of [Unit] section options:

$ man systemd.unit

Important `[Install]` Section Options

Option	Description
`Alias`	A space-separated list of additional names for the unit. Most `systemctl` commands, excluding `systemctl enable`, can use aliases instead of the actual unit name.
`RequiredBy`, `WantedBy`	The current service will be started when the listed services are started. See the description of `Wants` and `Requires` in the `[Unit]` section for details.
`Also`	Specifies a list of units to be enabled or disabled along with this unit when a user runs `systemctl enable` or `systemctl disable`.

A complete list of [Install] section options:

$ man systemd.unit

Important `[Service]` Section Options

Option	Description
`Type`	Configures the process start-up type. One of: `simple` (default) – starts the service immediately. It is expected that the main process of the service is defined in `ExecStart`. `forking` – considers the service started up once the process forks and the parent has exited. `oneshot` – similar to `simple`, but it is expected that the process has to exit before systemd starts follow-up units (useful for scripts that do a single job and then exit). You may want to set `RemainAfterExit=yes` as well so that systemd still considers the service as active after the process has exited. `dbus` – similar to `simple`, but considers the service started up when the main process gains a D-Bus name. `notify` – similar to `simple`, but considers the service started up only after it sends a special signal to systemd. `idle` – similar to `simple`, but the actual execution of the service binary is delayed until all jobs are finished.
`ExecStart`	Commands with arguments to execute when the service is started. `Type=oneshot` enables specifying multiple custom commands that are then executed sequentially. `ExecStartPre` and `ExecStartPost` specify custom commands to be executed before and after `ExecStart`.
`ExecStop`	Commands to execute to stop the service started via `ExecStart`.
`ExecReload`	Commands to execute to trigger a configuration reload in the service.
`Restart`	With this option enabled, the service shall be restarted when the service process exits, is killed, or a timeout is reached with the exception of a normal stop by the `systemctl stop` command.
`RemainAfterExit`	If set to `True`, the service is considered active even when all its processes exited. Useful with `Type=oneshot`. Default value is `False`.

A complete list of [Service] section options:

$ man systemd.service