Common commands

• Start a service now
  sudo systemctl start nginx.service

• Stop a service now
  sudo systemctl stop nginx.service

• Restart (stop then start)
  sudo systemctl restart nginx.service

• Reload configuration (if supported) without full restart
  sudo systemctl reload nginx.service

• Check status (shows active state and logs)
  systemctl status nginx.service

• Show recent journal logs for a unit
  journalctl -u nginx.service

• Follow logs in real time
  journalctl -u nginx.service -f


Enable/disable at boot

• Enable service to start on boot
  sudo systemctl enable nginx.service

• Disable service from starting on boot
  sudo systemctl disable nginx.service

• Enable and start immediately
  sudo systemctl enable --now nginx.service

• Mask a service (prevent any activation)
  sudo systemctl mask nginx.service

• Unmask
  sudo systemctl unmask nginx.service


Inspect and list units

• List all loaded units
  systemctl list-units

• List all unit files (enabled/disabled)
  systemctl list-unit-files

• Show unit properties
  systemctl show nginx.service


Boot targets (runlevels)

• Show current target
  systemctl get-default

• Set default target (e.g., multi-user or graphical)
  sudo systemctl set-default multi-user.target

• Switch to a target immediately
  sudo systemctl isolate multi-user.target


Power management

• Reboot now
  sudo systemctl reboot

• Power off
  sudo systemctl poweroff

• Suspend
  sudo systemctl suspend


Useful flags and tips

• Unit name can omit the suffix for common types (systemctl status nginx).
• Use –now with enable/disable to act immediately.
• Use –no-pager to prevent paging of output: systemctl status nginx –no-pager
• Check exit status ($?) after commands in scripts; many commands require sudo.
• journalctl shows systemd logs; combine with -u to focus on a unit.

Examples

• Start nginx, check status, follow logs:
  sudo systemctl start nginx
systemctl status nginx
journalctl -u nginx -f

• Enable and start a custom service file:
  sudo cp myapp.service /etc/systemd/system/
sudo systemctl daemon-reload
sudo systemctl enable --now myapp.service

• Debug a failing service (show full logs and properties):
  systemctl status myapp.service --no-pager
journalctl -u myapp.service --since "1 hour ago"
systemctl show myapp.service