🕐 Systemd Timers

# List all active timers with next/last trigger times
systemctl list-timers

# List ALL timers including inactive
systemctl list-timers --all

# Check status of a specific timer
systemctl status dnf-makecache.timer
systemctl status logrotate.timer

# See what timers are installed on the system
find /etc/systemd/system /lib/systemd/system -name "*.timer" | sort

A complete example — nightly backup running at 2 AM:

# Step 1: Create the service unit (what to run)
sudo tee /etc/systemd/system/nightly-backup.service << 'EOF'
[Unit]
Description=Nightly Backup Job
After=network.target

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

# Step 2: Create the timer unit (when to run)
sudo tee /etc/systemd/system/nightly-backup.timer << 'EOF'
[Unit]
Description=Run nightly backup at 2 AM
Requires=nightly-backup.service

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

[Install]
WantedBy=timers.target
EOF

# Step 3: Reload systemd and enable the timer
sudo systemctl daemon-reload
sudo systemctl enable --now nightly-backup.timer

# Step 4: Verify
systemctl list-timers nightly-backup.timer
systemctl status nightly-backup.timer

OnCalendar uses systemd's calendar expression syntax — more powerful than cron's 5-field format:

# Basic calendar expressions
OnCalendar=daily                  # every day at midnight
OnCalendar=weekly                 # every Monday at midnight
OnCalendar=monthly                # first of month at midnight
OnCalendar=hourly                 # every hour on the hour
OnCalendar=minutely               # every minute

# Specific time
OnCalendar=*-*-* 02:30:00        # every day at 2:30 AM
OnCalendar=*-*-* 06,18:00:00     # 6 AM and 6 PM daily
OnCalendar=Mon *-*-* 08:00:00    # every Monday at 8 AM
OnCalendar=Mon-Fri *-*-* 08:00:00 # weekdays at 8 AM

# Specific date
OnCalendar=2026-12-31 23:59:00   # once on New Year's Eve
OnCalendar=*-01-01 00:00:00      # every Jan 1st (yearly)
OnCalendar=*-*-01 00:00:00      # first of every month

# Intervals
OnCalendar=*:0/15                 # every 15 minutes
OnCalendar=*:00/5                 # every 5 minutes

# Verify your calendar expression
systemd-analyze calendar "Mon-Fri *-*-* 08:00:00"
systemd-analyze calendar "*:0/15"

Monotonic timers fire relative to system events rather than wall-clock time — perfect for tasks that should run after boot or at regular intervals from startup:

# Timer that runs 5 minutes after boot
sudo tee /etc/systemd/system/post-boot-check.timer << 'EOF'
[Unit]
Description=Run post-boot checks 5 minutes after startup

[Timer]
OnBootSec=5min
Unit=post-boot-check.service

[Install]
WantedBy=timers.target
EOF

# Timer that runs 15 minutes after boot, then every hour
sudo tee /etc/systemd/system/hourly-poll.timer << 'EOF'
[Unit]
Description=Poll service every hour starting 15min after boot

[Timer]
OnBootSec=15min
OnUnitActiveSec=1h

[Install]
WantedBy=timers.target
EOF

Persistent=true is the anacron equivalent for systemd timers — if the system was off when the timer should have fired, it fires immediately on next boot:

# Timer with Persistent=true — fires immediately on boot if missed
sudo tee /etc/systemd/system/weekly-report.timer << 'EOF'
[Unit]
Description=Weekly report — fires even if system was off

[Timer]
OnCalendar=Mon *-*-* 06:00:00
Persistent=true
RandomizedDelaySec=300

[Install]
WantedBy=timers.target
EOF

# Check when a timer last ran and whether it was missed
systemctl show nightly-backup.timer | grep -E "LastTrigger|NextElapse|Result"

# Enable and start a timer
sudo systemctl enable --now nightly-backup.timer

# Disable a timer (stops it running at boot)
sudo systemctl disable nightly-backup.timer

# Stop a running timer temporarily
sudo systemctl stop nightly-backup.timer

# Manually trigger the service NOW (for testing)
sudo systemctl start nightly-backup.service

# Check timer status
systemctl status nightly-backup.timer

# Check service logs
journalctl -u nightly-backup.service
journalctl -u nightly-backup.service -n 50
journalctl -u nightly-backup.service --since today

# Check both timer and service logs together
journalctl -u nightly-backup.timer -u nightly-backup.service

Systemd timers can run as regular users — no root required:

# Create user timer directories
mkdir -p ~/.config/systemd/user/

# Create user service
cat > ~/.config/systemd/user/sync-notes.service << 'EOF'
[Unit]
Description=Sync notes to remote

[Service]
Type=oneshot
ExecStart=/usr/bin/rsync -av ~/notes/ user@remote:/backup/notes/
EOF

# Create user timer
cat > ~/.config/systemd/user/sync-notes.timer << 'EOF'
[Unit]
Description=Sync notes every 30 minutes

[Timer]
OnBootSec=5min
OnUnitActiveSec=30min
Persistent=true

[Install]
WantedBy=timers.target
EOF

# Enable and start (no sudo needed)
systemctl --user daemon-reload
systemctl --user enable --now sync-notes.timer

# Check status
systemctl --user list-timers
systemctl --user status sync-notes.timer
journalctl --user -u sync-notes.service

# Enable linger so user timers survive logout
loginctl enable-linger $USER

Converting existing cron jobs to systemd timers:

# OLD cron job:
# 30 2 * * * root /usr/local/bin/nightly-backup.sh

# NEW — nightly-backup.service
cat > /etc/systemd/system/nightly-backup.service << 'EOF'
[Unit]
Description=Nightly Backup
After=network.target

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

# NEW — nightly-backup.timer
cat > /etc/systemd/system/nightly-backup.timer << 'EOF'
[Unit]
Description=Nightly Backup Timer
Requires=nightly-backup.service

[Timer]
OnCalendar=*-*-* 02:30:00
Persistent=true

[Install]
WantedBy=timers.target
EOF

sudo systemctl daemon-reload
sudo systemctl enable --now nightly-backup.timer