Which command is used to enable a service to start automatically during system boot?

The command to enable a service to start automatically during system boot is "systemctl enable servicename.service." This command creates the necessary symbolic links in the system's initialization directories, ensuring that the specified service is started when the system boots up.

When you execute this command, it essentially informs the system's initialization process of the desired behavior regarding the service's state during startup. This is crucial for services that need to be running from the moment the system is operational, such as database services, web servers, or any other essential component of the system.

In contrast, starting a service with "systemctl start servicename.service" only initiates the service for the current session; it does not affect its state during the next boot. Restarting a service using "systemctl restart servicename.service" temporarily stops and then starts the service again but does not alter the service's enabled or disabled status at boot. Finally, disabling a service with "systemctl disable servicename.service" prevents it from starting automatically during boot, which is the opposite of what is required for enabling a service.