Systemd Timer: Modern Alternative to Cron

Use systemd timers to schedule periodic tasks. More reliable than cron: integrated logs, dependencies, error handling and automatic retries.

systemd timers are the modern alternative to cron. Each timer is linked to a .service unit and executed by systemd: with complete logs on journald, error handling and the ability to define dependencies between services.

Basic structure

A systemd timer requires two files:

.service: defines what to execute
.timer: defines when to execute it

Example: daily backup script

Service file

cat > /etc/systemd/system/backup-daily.service << 'EOF'
[Unit]
Description=Daily server backup
After=network.target

[Service]
Type=oneshot
User=root
ExecStart=/usr/local/bin/backup.sh
StandardOutput=journal
StandardError=journal
EOF

Timer file

cat > /etc/systemd/system/backup-daily.timer << 'EOF'
[Unit]
Description=Run backup every day at 2:00
Requires=backup-daily.service

[Timer]
OnCalendar=*-*-* 02:00:00
Persistent=true

[Install]
WantedBy=timers.target
EOF

Activation

systemctl daemon-reload
systemctl enable --now backup-daily.timer

# Verify
systemctl status backup-daily.timer

OnCalendar syntax

The OnCalendar syntax is more readable than cron:

# Every day at 3:30
OnCalendar=*-*-* 03:30:00

# Every Monday at 8:00
OnCalendar=Mon *-*-* 08:00:00

# First of every month at midnight
OnCalendar=*-*-01 00:00:00

# Every hour
OnCalendar=hourly

# Every day
OnCalendar=daily

# Every week (Monday at 00:00)
OnCalendar=weekly

# Every 15 minutes
OnCalendar=*:0/15

# Every 6 hours
OnCalendar=0/6:00:00

# Monday-Friday at 9:00
OnCalendar=Mon..Fri *-*-* 09:00:00

Verify syntax

# Check when the timer will trigger
systemd-analyze calendar "*-*-* 02:00:00"
systemd-analyze calendar "Mon *-*-* 08:00:00"

Relative timers (OnBootSec, OnUnitActiveSec)

[Timer]
# Run 5 minutes after boot
OnBootSec=5min

# Then every 30 minutes
OnUnitActiveSec=30min

Persistent=true

[Timer]
OnCalendar=daily
Persistent=true

Persistent=true means: if the timer didn't trigger at the scheduled time (server was off), run it immediately at next boot. Equivalent to cron's MAILTO option to not miss executions.

Timer management

# List all active timers
systemctl list-timers

# List all timers (including inactive)
systemctl list-timers --all

# Status of specific timer
systemctl status backup-daily.timer

# Run the service immediately (without waiting for timer)
systemctl start backup-daily.service

# Service logs
journalctl -u backup-daily.service -n 50

# Real-time logs
journalctl -u backup-daily.service -f

# Disable the timer
systemctl disable --now backup-daily.timer

Practical examples

Weekly log cleanup

# /etc/systemd/system/clean-logs.service
[Unit]
Description=Clean old logs

[Service]
Type=oneshot
ExecStart=/usr/bin/find /var/log -name "*.log" -mtime +30 -delete
ExecStart=/usr/bin/journalctl --vacuum-time=30d

# /etc/systemd/system/clean-logs.timer
[Unit]
Description=Weekly log cleanup

[Timer]
OnCalendar=Sun *-*-* 04:00:00
Persistent=true

[Install]
WantedBy=timers.target

Automatic updates

# /etc/systemd/system/auto-update.service
[Unit]
Description=Automatic system updates

[Service]
Type=oneshot
ExecStart=/usr/bin/apt update
ExecStart=/usr/bin/apt upgrade -y
ExecStart=/usr/bin/apt autoremove -y

# /etc/systemd/system/auto-update.timer
[Timer]
OnCalendar=*-*-* 03:00:00
Persistent=true

[Install]
WantedBy=timers.target

Cron vs systemd timer

	Cron	Systemd Timer
Logs	❌ Only via syslog	✅ integrated journald
Retry on error	❌ No	✅ With `Restart=on-failure`
Dependencies	❌ No	✅ `After=`, `Requires=`
Persistent	❌ Skips if offline	✅ Catches up at boot
Simplicity	✅ One line	⚠️ Two files
Familiar	✅ Everyone knows it	⚠️ Learning curve

For simple tasks without special requirements, cron is still valid. For critical tasks where logs and reliability matter, use systemd timers.

Systemd Timer: Modern Alternative to Cron

On this page