Tool cheatsheet

systemd and journalctl Cheatsheet

Manage services, read logs, schedule timers and write unit files on Linux systems that use systemd.

Managing services

Check a service — Show whether a service is running, with its latest log lines.
Start a service — Start a service right now.
Stop a service — Stop a running service right now.
Restart a service — Stop and start a service.
Reload a service's configuration — Ask a service to reload its configuration without restarting, if it supports that.
Start a service now and at boot — Enable a service for boot and start it immediately.
Stop starting a service at boot — Disable a service from starting at boot. Add --now to also stop it.
Test if a service is running — Print active or inactive; the exit code suits scripts.
List failed units — Show units that have failed.
List running services — Show all service units that are loaded and running.
Prevent a service from starting — Link the unit to /dev/null so nothing can start it, even manually.
Manage your own user services — Use the per-user service manager, with no sudo.

Show a service's logs — Show all log entries for a unit.
Follow a service's logs — Stream new log entries as they arrive.
Show recent entries only — Show entries from the last hour.
Show errors from this boot — Show messages of priority error and worse since the last boot.
Show the previous boot's logs — Read logs from the boot before this one, for example after a crash.
Show kernel messages — Show kernel log entries, like dmesg.
Show the latest lines — Show the last 100 lines without paging.
Check how much space logs use — Show the disk space used by the journal.
Delete old logs — Remove journal entries older than seven days.

Write a service unit — A service that runs an app as its own user and restarts it on failure. Save it as /etc/systemd/system/myapp.service.
Reload unit files — Make systemd re-read unit files after you create or change one.
Override a unit safely — Create a drop-in override file instead of editing the packaged unit.
Show a unit's effective definition — Print the unit file and its drop-ins.
Write a timer — Run a service every day at 03:00, and catch up after downtime. Pair it with a myjob.service.
List timers — Show timers with their next and last run times.
Check a unit file for errors — Check a unit file for mistakes.
Test a calendar expression — Show when an OnCalendar expression will next fire.
Keep user services running after logout — Let a user's services start at boot and keep running without a login session.

See what slows boot — List units by how long they took to start.
Show the boot critical path — Show the chain of units that determined boot time.
Show or set the hostname — Show the hostname and OS details. Set one with hostnamectl set-hostname.
Show the date, time and timezone — Show time settings and whether the clock is synchronized.
Set the timezone — Change the system timezone.

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