Starting, stopping and checking the programs that run your server.
THE COMMON OPERATIONS
systemctl status names the service and reports whether it is running, when it started, and recent log lines. This is where to look first when something is not working. systemctl start begins a service systemctl stop halts it systemctl restart stops and starts it systemctl reload re-reads configuration without dropping connections, where the service supports it
Prefer reload over restart for a web server on a live site; it applies configuration changes without interrupting requests.
ENABLING AT BOOT
systemctl enable makes a service start automatically after a reboot. systemctl disable prevents it.
A service that is running but not enabled disappears after the next reboot, which is a confusing failure.
CHECKING WHAT IS RUNNING
systemctl list-units --type=service shows active services.
AFTER A CONFIGURATION CHANGE
Test the configuration first where the service offers it, then reload. Restarting with a broken configuration takes the service down and it will not come back.
