systemd and journalctl cheatsheet

systemd and journalctl: Unit files and timers

9 common systemd and journalctl tasks.

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.

[Unit]
Description=My app
After=network-online.target
Wants=network-online.target

[Service]
User=myapp
WorkingDirectory=/opt/myapp
ExecStart=/opt/myapp/bin/myapp
Restart=on-failure
RestartSec=5

[Install]
WantedBy=multi-user.target

Reload unit files

Make systemd re-read unit files after you create or change one.

sudo systemctl daemon-reload

Override a unit safely

Create a drop-in override file instead of editing the packaged unit.

sudo systemctl edit nginx

Show a unit's effective definition

Print the unit file and its drop-ins.

systemctl cat nginx

Write a timer

Run a service every day at 03:00, and catch up after downtime. Pair it with a myjob.service.

[Unit]
Description=Run myjob daily

[Timer]
OnCalendar=*-*-* 03:00:00
Persistent=true

[Install]
WantedBy=timers.target

List timers

Show timers with their next and last run times.

systemctl list-timers

Check a unit file for errors

Check a unit file for mistakes.

systemd-analyze verify /etc/systemd/system/myapp.service

Test a calendar expression

Show when an OnCalendar expression will next fire.

systemd-analyze calendar "Mon..Fri 09:00"

Keep user services running after logout

Let a user's services start at boot and keep running without a login session.

sudo loginctl enable-linger myuser