What final action does the command 'kill [PID]' perform?

The command 'kill [PID]' is specifically designed to send a signal to terminate a process identified by the provided process ID (PID). By default, it sends the TERM (terminate) signal, which instructs the operating system to stop the process gracefully. If the process does not respond to this signal, the administrator can use additional options to send different signals, such as KILL, which forcefully terminates the process without allowing it to clean up resources.

This command is vital for managing processes within a Linux system, allowing users to control which processes are running and to free up system resources by terminating processes that are no longer needed or are misbehaving.

Other options do not align with the primary function of the kill command. Restarting a process isn't something that 'kill' directly does; instead, a separate command or combination of commands would be used for that purpose. Changing a process's priority would typically involve the 'nice' or 'renice' commands. Lastly, displaying the process tree is accomplished using commands like 'ps' or 'top', not 'kill'.