Systemd - Scheduling tasks using timers

Systemd-Timers are a more flexible alternative to cronjobs. For example, Systemd will take care of the dependencies and the logging of your timer whereas with cron you'd have to program it yourself.

In this example, I will use systemd-timers to create a backup of the zabbix PostgreSQL database.

First, create the service that will actually run the task:

 [root@zabbix ~]# cat << EOF >> /etc/systemd/system/zabbix-db-backup.service  
 [Unit]  
 Description=Create a Backup of the zabbix database  
 After=network-online.target postgresql.service  
 [Service]  
 Type=simple  
 Nice=19  
 ExecStart=/usr/bin/sh /root/scripts/zabbix-db-backup.sh  
 User=root  
 Group=root
 EOF  

Now create the timer unit which is responsible for scheduling your service:

 [root@zabbix ~]# cat << EOF >> /etc/systemd/system/zabbix-db-backup.timer  
 [Unit]  
 Description=Timer for zabbix-db-backup.service  
 [Timer]  
 OnCalendar=*-*-* *:45:00  
 Unit=zabbix-db-backup.service  
 Persistent=true
 [Install]  
 WantedBy=timers.target  
 EOF  

You can check your time and date syntax using 'systemd-analyze calendar', here's an example:

 [root@zabbix ~]# systemd-analyze calendar '*-*-* *:45:00'  
 Normalized form: *-*-* *:45:00  
   Next elapse: Thu 2022-07-28 01:45:00 CEST  
     (in UTC): Wed 2022-07-27 23:45:00 UTC  
     From now: 25min left  

Reload Systemd to make it aware of the new config files:

 [root@zabbix ~]# systemctl daemon-reload  

Once Systemd is reloaded, test your task to make sure it works:

 [root@zabbix ~]# systemctl start zabbix-db-backup.service  

As mentioned earlier, Systemd takes care of logging which can be checked using 'journalctl':

 [root@zabbix ~]# journalctl -f -u zabbix-db-backup.service  

For the final step, enable the timer-unit so that the timer unit will start after

rebooting the server:

 [root@zabbix ~]# systemctl enable --now zabbix-db-backup.timer  

Feel free to comment and / or suggest a topic.