Working with systemd timers

Before you set up a systemd timer unit, you need to create a systemd service unit that controls the shell script. To do this, open a new text file for editing and add the following service unit definition:

[Unit]
Description="Hello World script"

[Service]
ExecStart=/usr/local/bin/helloworld.sh

Save the file under the name helloworld.service in the directory /etc/systemd/system/.

Open a new text file for editing and add the following timer definition:

[Unit]
Description="Run Hello World script"

[Timer]
OnBootSec=5min
OnUnitActiveSec=24h
Unit=helloworld.service

[Install]
WantedBy=multi-user.target

The [Timer] section in the example above specifies what service to trigger (helloworld.service) and when to trigger it. In this case, the option OnBootSec specifies a monotonic timer that triggers the service five minutes after the system boot, while the option OnUnitActiveSec triggers the service 24 hours after the service has been activated (that is, the timer will trigger the service once a day). Finally the option WantedBy specifies that the timer should start when the system has reached the multi-user target.

Save the timer unit file under the name helloworld.timer in the /etc/systemd/system/ directory. To check the correctness of the created unit files, run the following command:

> sudo  systemd-analyze verify /etc/systemd/system/helloworld.*

If the command returns no output, the files have passed the verification successfully.

To start the timer, use the command sudo systemctl start helloworld.timer. To enable the timer on boot, run the command sudo systemctl enable helloworld.timer.