systemctl — Beginner's Guide (with Nginx Examples)

What is systemctl?

systemctl is the command-line tool used to control and manage systemd, the system and service manager used in many Linux distros like Ubuntu, Fedora, and Debian.

It lets you:

• Start, stop, restart, and check status of services (like Nginx)
• Enable or disable services to start on boot
• Manage system power actions (reboot, shutdown)
• Manage system states and units (services, sockets, timers, etc.)

Basic Terminology

• Service: A background program like the web server Nginx (nginx.service), database (mysql.service), or SSH (ssh.service).
• Unit: systemd managed object such as services, mounts, devices, or timers.
• Enable: Set a service to start automatically when the system boots.
• Disable: Prevent a service from starting automatically on boot.
• Mask: Prevent a service from starting manually or automatically.
• Status: Shows the current running state and logs of a service.