systemd Timers: Replacing cron Jobs with Scheduled Units, Failure Alerts, and Logs

# Two files form a pair
/etc/systemd/system/mybackup.service   # The job to run
/etc/systemd/system/mybackup.timer     # The schedule

# /etc/systemd/system/mybackup.service
[Unit]
Description=Daily database backup
After=network.target postgresql.service

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

# /etc/systemd/system/mybackup.timer
[Unit]
Description=Run mybackup daily at 3am

[Timer]
OnCalendar=*-*-* 03:00:00     # Every day at 03:00
Persistent=true                # Catch up immediately on missed runs
RandomizedDelaySec=300         # Random delay of up to 5 minutes (spread load)
Unit=mybackup.service          # Optional (auto-linked by matching name)

[Install]
WantedBy=timers.target

# Enable and start
sudo systemctl daemon-reload
sudo systemctl enable --now mybackup.timer

# Check status
systemctl status mybackup.timer
systemctl list-timers

*-*-* 00:00:00       # Every day at midnight
*-*-* 03:00:00       # Every day at 03:00
Mon *-*-* 09:00:00   # Every Monday at 09:00
*-*-1 00:00:00       # The 1st of every month at midnight
*-*-* 0/6:00:00      # Every 6 hours
hourly               # Top of every hour (= *-*-* *:00:00)
daily                # Every day at midnight (= *-*-* 00:00:00)
weekly               # Every Monday at midnight
monthly              # The 1st of every month at midnight

# Validate expressions
systemd-analyze calendar "*-*-* 03:00:00"
systemd-analyze calendar "Mon *-*-* 09:00:00"

[Timer]
OnBootSec=5min         # Run once 5 minutes after boot
OnUnitActiveSec=1h     # Then repeat every hour

# Add to mybackup.service
[Unit]
OnFailure=notify-failure@%n.service

# /etc/systemd/system/notify-failure@.service
[Unit]
Description=Failure notification for %i

[Service]
Type=oneshot
ExecStart=/usr/local/bin/notify-slack.sh "Timer %i failed"

# Full timer list (including next run time)
systemctl list-timers --all

# Service logs
journalctl -u mybackup.service --since today
journalctl -u mybackup.service -n 50

# Run immediately by hand (independent of the timer)
sudo systemctl start mybackup.service

# Stop only the timer (keep the service)
sudo systemctl stop mybackup.timer
sudo systemctl disable mybackup.timer