systemd is a system and service manager

Management

Executing service management commands without understanding consequences will break installation.

• Shows list of units systemctl
• Shows status of specific unit systemctl status UNIT_NAME
• Starts specific unit sudo systemctl start UNIT_NAME Unit will not start on boot unless enabled; inspect status of services and timers via systemctl status.
• Restarts specific unit sudo systemctl restart UNIT_NAME
• Stops specific unit sudo systemctl stop UNIT_NAME
• Reloads specific unit (updates used configuration, if supported) sudo systemctl reload UNIT_NAME
• Enables specific unit sudo systemctl enable UNIT_NAME
• Disables specific unit sudo systemctl disable UNIT_NAME
• Reloads systemd manager configuration sudo systemctl daemon-reload

systemd allows for user-level services (managed via --user modifier). Note that user services will only run when there's user session; session lingering is available via sudo loginctl enable-linger although to make systemctl --user to be available, following should be appended to .bashrc: export XDG_RUNTIME_DIR="/run/user/$UID" export DBUS_SESSION_BUS_ADDRESS="unix:path=${XDG_RUNTIME_DIR}/bus" Such services operate not from from /etc/systemd/ but from /home/$USER/.config/systemd/user/

Logs

• Shows systemd logs journalctl
• Shows logs of the systemd service/timer journalctl -u UNIT_NAME.service -f switch allow to continue to follow logs of service/timer
• Shows logs of specific service for specific time period journalctl -u UNIT_NAME.service -S 'since' -U 'until'

Services

Instructions how to add custom systemd service

1. Create file /etc/systemd/system/SERVICE_NAME.service

   [Unit]
   After=network.target
   StartLimitIntervalSec=0
   StartLimitBurst=5
   Wants=SERVICE_NAME.timer
   
   [Service]
   Type=simple
   Restart=always
   RestartSec=1
   User=USER
   Group=GROUP
   ExecStart=/bin/bash PATH_TO_EXECUTABLE
   
   [Install]
   WantedBy=multi-user.target

2. Enable service and start it via sudo systemctl enable --now SERVICE_NAME.service

Timers

Instructions how to make custom systemd service run on specified schedule (modern alternative to CRON scheduling)

External sources: https://wiki.archlinux.org/title/Systemd/Timers

1. Create file /etc/systemd/system/SERVICE_NAME.timer

   [Unit]
   Description=Run foo weekly
   Requires=SERVICE_NAME.service
   
   [Timer]
   Unit=SERVICE_NAME.service
   OnCalendar=weekly
   Persistent=true
   
   [Install]
   WantedBy=timers.target

   OnCalendar - every minute is *-*-* *:*:00, use systemd-analyze calendar "query" to check

2. Enable and start timer via sudo systemctl enable --now SERVICE_NAME.timer

   This will run service out-of-schedule once, immediately.

Last update: 2024-06-17