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How to replace Cron by SystemD

Use systemd to schedule automated tasks

📌 Overview

On modern Linux systems, systemd timers can fully replace cron jobs. Timers give you:

  • Better logging (journalctl)
  • Service dependencies (After=, Requires=)
  • Reliable scheduling after boot
  • Random delays to avoid load spikes
  • Clear control (start, stop, enable, status)

This guide explains how to create a scheduled task using systemd.

1. Create a systemd Service

The service defines what will run — usually a script or command.

Example file:
/etc/systemd/system/myscript.service

[Unit]
Description=Run my custom script

[Service]
Type=oneshot
ExecStart=/usr/local/bin/myscript.sh

Make your script executable:

chmod +x /usr/local/bin/myscript.sh

2. Create a systemd Timer

The timer defines when the service runs.

File:
/etc/systemd/system/myscript.timer

[Unit]
Description=Run my script every day at 03:00

[Timer]
OnCalendar=03:00
Persistent=true

[Install]
WantedBy=timers.target

Persistent=true ensures missed runs (e.g., machine off) are executed at the next boot.

3. Enable and Start the Timer

Reload systemd and activate the timer:

systemctl daemon-reload
systemctl enable --now myscript.timer

4. Verify the Timer is Working

List active timers:

systemctl list-timers

View logs for the executed service:

journalctl -u myscript.service

5. Useful Scheduling Examples

Run Daily at 3 AM

OnCalendar=03:00

Run Every 15 Minutes

OnCalendar=*:0/15

Run Every Monday at 09:00

OnCalendar=Mon 09:00

Run on Reboot (after 5 minutes)

OnBootSec=5min

Run Hourly

OnCalendar=hourly

Run Monthly

OnCalendar=monthly

6. Example: Run a Script Every 30 Minutes

/etc/systemd/system/healthcheck.service

[Unit]
Description=Health check script

[Service]
Type=oneshot
ExecStart=/usr/local/bin/healthcheck.sh

/etc/systemd/system/healthcheck.timer

[Unit]
Description=Run health check every 30 minutes

[Timer]
OnCalendar=*:0/30

[Install]
WantedBy=timers.target

Enable:

systemctl enable --now healthcheck.timer

7. Troubleshooting

Check Timer Status

systemctl status myscript.timer

Check Service Logs

journalctl -u myscript.service

Manually Trigger the Task

systemctl start myscript.service

✔ Summary

systemd timers are a robust and modern alternative to classic cron:

  • More control
  • Better logging
  • Cleaner dependency management
  • Easier to maintain
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