$ Linux Command

System

systemctl

Inspect and control systemd services and units.

systemdservicestartstopenablelogsboot

Additional Notes

systemctl controls systemd, the service manager used by many Linux distributions. It starts, stops, restarts, enables, disables, and inspects services and other unit types.

A service can be running right now without being enabled at boot. Likewise, a service can be enabled at boot but currently stopped. This difference is important.

Syntax

systemctl [command] [unit]
sudo systemctl [command] [unit]

Parameters

  • command: Action such as status, start, stop, restart, enable, or disable.
  • unit: A systemd unit name, commonly a service such as ssh.service or nginx.service.

The .service suffix is often optional:

systemctl status ssh
systemctl status ssh.service

Common Commands

  • status UNIT: Show state, PID, recent logs, and whether the unit is enabled.
  • start UNIT: Start a service now.
  • stop UNIT: Stop a service now.
  • restart UNIT: Stop and start a service.
  • reload UNIT: Reload configuration without a full restart when supported.
  • enable UNIT: Start automatically at boot.
  • disable UNIT: Do not start automatically at boot.
  • is-active UNIT: Print whether a unit is active.
  • is-enabled UNIT: Print whether a unit is enabled for boot.
  • list-units: Show active units.
  • list-unit-files: Show installed unit files and enable state.
  • daemon-reload: Reload systemd unit files after editing them.

Examples

systemctl status nginx

Inspect the current state of nginx.

sudo systemctl start nginx

Start nginx now.

sudo systemctl restart ssh

Restart the SSH service.

sudo systemctl enable docker

Make Docker start automatically at boot.

sudo systemctl enable --now docker

Enable Docker at boot and start it immediately.

systemctl list-units --type=service

List active services.

systemctl list-unit-files --type=service

List installed service unit files and their enable/disable state.

journalctl -u ssh --since today

Read logs for a service. This uses journalctl, but it is often part of the same troubleshooting workflow.

Practical Notes

  • Most service changes need sudo.
  • Run systemctl status UNIT before restarting important services.
  • Use restart after many config changes, but use reload when the service supports reload and you want less disruption.
  • After editing a unit file, run sudo systemctl daemon-reload.
  • If a service fails, check systemctl status UNIT and journalctl -u UNIT.