If you change a configuration file for a system service, it is usually necessary to stop and restart the service to make it read the new configuration. If you are reconfiguring the X server, it is often convenient to change from runlevel 2 to runlevel 1 to make testing easier and then switch back to runlevel 2 to reenable the graphical login. If a service is improperly configured, it is easier to stop and restart it until you have it configured correctly than it is to reboot the entire machine.
The traditional way to manage a service (as root) is to call the service’s
/etc/init.d name on the command line with an appropriate keyword, such as
stop. For example, to start the Apache web server, ...