systemd is the first process Linux starts (PID 1) and the manager for every service after it. If something runs in the background on a modern Linux box, systemd is supervising it.
The essentials
systemctl status nginx # is it running? recent logs
systemctl start|stop|restart nginx
systemctl enable --now nginx # start now + on every boot
journalctl -u nginx -f # live logs for a serviceA unit file
/etc/systemd/system/myapp.service:
[Unit]
Description=My App
After=network-online.target
[Service]
ExecStart=/usr/bin/myapp
Restart=always
User=appuser
[Install]
WantedBy=multi-user.targetsudo systemctl daemon-reload && sudo systemctl enable --now myappSystem vs user services
| Scope | Command | Runs |
|---|---|---|
| System | systemctl |
At boot, as root/specified user |
| User | systemctl --user |
When the user is logged in… |
User services need lingering (
loginctl enable-linger user) to survive logout — a classic gotcha. See Building MCP Servers as systemd User Services.
Related: The Linux Boot Process · Cron and Scheduling · Building MCP Servers as systemd User Services