Systemd: create a unit/service

In this tutorial you will learn to create services with systemd, so your scripts can be executed during system boot.

To do this, you need to create a <service-name>.service file in /etc/systemd/system/. This is a template of the file content:

[Unit]
Description=service description

[Service]
ExecStart=command

[Install]
WantedBy=multi-user.target

[Unit]

Description: A brief description of the service.
Wants: Declare “weak” dependencies requirement.
Requires: Declare “strong” dependencies requirement.
After: Declare that service can be started only when other service/unit finish its startup. For example, After: network.target means service will start after network is configured.
Before: the inverse of After.
OnFailure: A space-separated list of one or more units that are activated when this unit enters the “failed” state.
OnSuccess: A space-separated list of one or more units that are activated when this unit enters the “inactive” state.
StartLimitIntervalSec: seconds / StartLimitBurst: number: A service can’t be started more than “number” times in a “seconds” interval.

Type: start-up type. Default option is simple, more info about this in this link.
ExecStart: Command that is executed when this service is started.
Restart: indicates if service should be restarted when process exits cleanly (on-success), when process exits with a non-zero exit code (on-failure), should be restarted always (always) or never (no). Other values are on-abnormal, on-abort and on-watchdog.
RestartSec: Configures the time to sleep (in seconds) before restarting a service .
User: set the user that processes are executed as. Default is root.

This section is needed when you want to install your unit/service (systemctl enable).
WantedBy: is similar to After but is interpreted only during installation of the unit. Most used option is multi-user.target.

Once you’ve saved the file in /etc/systemd/system/, you need to reload systemd with sudo systemctl daemon-reload (you don’t need “sudo” if you are a “root” user).
Then, you can start your service with sudo systemctl start myserice.service, replacing myservice with your service filename.
If you want to install your service (service will start when computer boots up), type sudo systemctl enable myservice.service.
You can start and enable a service with one command: sudo systemctl enable --now myservice.service.

You can stop a service with sudo systemctl stop myservice.service.
To disable a service, so can’t be started when computer boots up, type sudo systemctl disable myservice.service.
When you uninstall some program, ensure that there are no orphaned units, and disable them if there are.

You can create services for specific users. Service files can be inside /etc/systemd/user/ (with root permissions) or ~/.config/systemd/user/.
Use WantedBy=default.target in the [Install] section.
When you manage these services, add --user to the systemctl commands.

Restart a service with sudo systemctl restart myservice.service.
Check service status with sudo systemctl status myservice.service.
Some services allow to reload its configuration without needing a restart (like httpd). In those cases, you can type sudo systemctl reload myservice.service.