Commands and Management

Learning Focus

By the end of this lesson you will be fluent in every command needed to manage timer units — from creation to cleanup, including schedule validation, log inspection, user timers, and bulk operations.

Standard Workflow

Every time you create or modify a timer unit, follow this sequence:

standard-workflow.sh

# 1. Create/edit the .timer and .service files
sudo nano /etc/systemd/system/myjob.timer
sudo nano /etc/systemd/system/myjob.service

# 2. Tell systemd to re-read unit files
sudo systemctl daemon-reload

# 3. Enable on boot and start now
sudo systemctl enable --now myjob.timer

# 4. Verify it appears in the timer list
systemctl list-timers myjob.timer --no-pager

# 5. Test the service manually
sudo systemctl start myjob.service

# 6. Check logs
journalctl -u myjob.service -n 20 --no-pager

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systemctl — Timer Management

Starting and Stopping

Command	Description
sudo systemctl start myjob.timer	Start the timer immediately
sudo systemctl stop myjob.timer	Stop the timer (won't disable on boot)
sudo systemctl restart myjob.timer	Stop and restart the timer

Enabling and Disabling

Command	Description
sudo systemctl enable myjob.timer	Enable on boot (does not start)
sudo systemctl enable --now myjob.timer	Enable on boot AND start now
sudo systemctl disable myjob.timer	Disable on boot (does not stop)
sudo systemctl disable --now myjob.timer	Disable AND stop

Enable the .timer, NOT the .service

Always enable the .timer, never the .service. Enabling the service directly would run it once at boot — not on a schedule.

# ✅ Correct
sudo systemctl enable --now myjob.timer

# ❌ Wrong — runs once at boot, no scheduling
sudo systemctl enable --now myjob.service

Checking Status

Command	Description
systemctl status myjob.timer --no-pager	Timer status: next run, last trigger
systemctl status myjob.service --no-pager	Service result: exit code, output
systemctl is-active myjob.timer	Returns active or inactive
systemctl is-enabled myjob.timer	Returns enabled or disabled

status-examples.sh

# Check when it will next fire
systemctl status myjob.timer --no-pager

# Check what happened on the last run
systemctl status myjob.service --no-pager

# Quick check in scripts
if systemctl is-active --quiet myjob.timer; then
    echo "Timer is running"
fi

Reloading

Command	Description
sudo systemctl daemon-reload	Re-read all unit files from disk

Always Reload After Changes

If you edit a unit file and forget daemon-reload, systemd uses the old version. This is the #1 cause of "I changed the config but nothing happened."

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Listing and Discovery

List All Timers

list-timers.sh

# List all timers with their schedule info
systemctl list-timers --all --no-pager

example-output.txt

NEXT                        LEFT          LAST                        PASSED      UNIT                    ACTIVATES
Mon 2026-03-02 02:15:00 UTC 2h 14min left Sun 2026-03-01 02:15:03 UTC 21h ago     wp-backup.timer         wp-backup.service
Mon 2026-03-02 00:05:00 UTC 4min left     Mon 2026-03-02 00:00:01 UTC 58s ago     health-check.timer      health-check.service
Mon 2026-03-02 03:00:00 UTC 2h 59min left Sun 2026-03-01 03:01:15 UTC 20h ago     certbot-renew.timer     certbot-renew.service

Column meanings:

Column	Meaning
NEXT	Next scheduled fire time
LEFT	Time remaining until NEXT
LAST	Last time the timer fired
PASSED	Time since LAST
UNIT	The timer unit name
ACTIVATES	The service it triggers

List Enabled Timers

list-enabled.sh

systemctl list-unit-files --type=timer --state=enabled

Show Timer Properties

show-properties.sh

# Machine-readable properties (for scripting)
systemctl show myjob.timer -p NextElapseUSecRealtime -p LastTriggerUSec -p Unit -p Triggers

# Show the unit file content
systemctl cat myjob.timer
systemctl cat myjob.service

# Show where the unit file is stored
systemctl show -p FragmentPath myjob.timer

Show Dependencies

dependencies.sh

systemctl list-dependencies myjob.timer
systemctl show -p Triggers myjob.timer

Testing the Service Immediately

test-now.sh

# Run the service without waiting for the timer
sudo systemctl start myjob.service

# Check the result
journalctl -u myjob.service -n 20 --no-pager

---

systemd-analyze — Schedule Validation

Validate OnCalendar Expressions

validate-schedule.sh

# Show the next 5 fire times
systemd-analyze calendar --iterations=5 'Mon..Fri 06:00'

# Validate common patterns
systemd-analyze calendar --iterations=3 'daily'
systemd-analyze calendar --iterations=3 '*:0/5'
systemd-analyze calendar --iterations=3 '*-*~1 00:00:00'
systemd-analyze calendar --iterations=5 '09,21:00'
systemd-analyze calendar --iterations=3 '*-*-* 08..20:0/10'

Verify Unit Files

verify-units.sh

sudo systemd-analyze verify /etc/systemd/system/myjob.timer
sudo systemd-analyze verify /etc/systemd/system/myjob.service

# Verify both at once
sudo systemd-analyze verify /etc/systemd/system/myjob.{timer,service}

No output means no errors. Errors print the exact line and directive:

error-example.txt

/etc/systemd/system/myjob.timer:5: Unknown key 'OnCalander' in section 'Timer'

Security Audit

security-audit.sh

systemd-analyze security myjob.service

Score: 0.0 = fully sandboxed, 10.0 = no sandboxing. Aim for below 3.0.

Boot Impact

boot-impact.sh

systemd-analyze blame | grep timer
systemd-analyze critical-chain timers.target

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journalctl — Log Management

Service Logs (Most Important)

The .service produces the real output. The .timer only logs activation events.

Command	Description
journalctl -u myjob.service	All logs from the service
journalctl -u myjob.service -n 50	Last 50 lines
journalctl -u myjob.service -f	Follow live output (like tail -f)
journalctl -u myjob.service --since "1 hour ago"	Logs from the last hour
journalctl -u myjob.service --since today	Today's logs
journalctl -u myjob.service --since "2026-03-01" --until "2026-03-02"	Date range
journalctl -u myjob.service -o json-pretty	JSON format
journalctl -u myjob.service -p err	Errors only

Timer Logs

timer-logs.sh

# When the timer fired
journalctl -u myjob.timer --since today --no-pager

Combined View

combined-logs.sh

# Both timer and service logs, interleaved by time
journalctl -u myjob.timer -u myjob.service --since today --no-pager

Log Priority Levels

Level	Flag	Meaning
Emergency	-p emerg	System unusable
Alert	-p alert	Immediate action required
Critical	-p crit	Critical conditions
Error	-p err	Error conditions
Warning	-p warning	Warning conditions
Notice	-p notice	Normal but significant
Info	-p info	Informational
Debug	-p debug	Debug-level

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User Timer Management

User timers run without root privileges:

Command	Description
systemctl --user daemon-reload	Reload user unit files
systemctl --user enable --now myjob.timer	Enable and start user timer
systemctl --user disable --now myjob.timer	Disable and stop user timer
systemctl --user status myjob.timer	Check status
systemctl --user list-timers --no-pager	List user timers
journalctl --user -u myjob.service	View user service logs

user-timer-workflow.sh

mkdir -p ~/.config/systemd/user/
# Place .timer and .service in ~/.config/systemd/user/
systemctl --user daemon-reload
systemctl --user enable --now my-timer.timer

Persistence After Logout

enable-linger.sh

# Keep user timers running after logout
sudo loginctl enable-linger "$USER"

# Check status
loginctl show-user "$USER" | grep Linger

# Disable
sudo loginctl disable-linger "$USER"

---

Persistent State Management

persistent-state.sh

# Clear stored timer state (reset Persistent catch-up tracking)
sudo systemctl clean --what=state myjob.timer

# Show timer timestamps (last trigger, next elapse)
systemctl show myjob.timer -p LastTriggerUSec -p NextElapseUSecRealtime

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Bulk Operations

Enable Multiple Timers

bulk-enable.sh

for unit in /etc/systemd/system/*.timer; do
    name=$(basename "$unit")
    sudo systemctl enable --now "$name"
done

Health Check All Timers

bulk-health.sh

systemctl list-timers --all --no-pager --no-legend | while read -r next left last passed unit activates rest; do
    echo "=== $unit ==="
    systemctl status "$unit" --no-pager 2>/dev/null | head -5
    echo
done

Full Cleanup

cleanup.sh

sudo systemctl disable --now myjob.timer
sudo rm /etc/systemd/system/myjob.timer
sudo rm /etc/systemd/system/myjob.service
sudo systemctl daemon-reload
sudo systemctl reset-failed

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Quick Command Reference

Task	Command
Reload unit files	sudo systemctl daemon-reload
Start timer	sudo systemctl start myjob.timer
Stop timer	sudo systemctl stop myjob.timer
Enable + start	sudo systemctl enable --now myjob.timer
Disable + stop	sudo systemctl disable --now myjob.timer
Check timer status	systemctl status myjob.timer --no-pager
Check service result	systemctl status myjob.service --no-pager
List all timers	systemctl list-timers --all --no-pager
Follow live logs	journalctl -u myjob.service -f
Last N log lines	journalctl -u myjob.service -n 50
Errors only	journalctl -u myjob.service -p err
Validate schedule	systemd-analyze calendar --iterations=5 'EXPR'
Verify unit syntax	sudo systemd-analyze verify myjob.timer
Show unit content	systemctl cat myjob.timer
Test service now	sudo systemctl start myjob.service
Security audit	systemd-analyze security myjob.service
Reset timer state	sudo systemctl clean --what=state myjob.timer
Reset failed	sudo systemctl reset-failed

Key Takeaways

• Always daemon-reload after editing unit files.
• Enable the .timer, not the .service.
• Use systemd-analyze calendar to validate every schedule before deploying.
• Use systemd-analyze verify to catch syntax errors before runtime.
• Check both .timer status (next/last run) and .service status (exit code, logs).
• Use systemctl list-timers --all for a system-wide overview.
• User timers need loginctl enable-linger for persistence after logout.

What's Next

• Practical Examples — 27 complete, copy-paste-ready examples covering every timer pattern.