What is the result of invoking the command 'kill -9 PID' on a process?

Invoking the command 'kill -9 PID' sends a SIGKILL signal to the specified process identified by the PID (Process ID). This signal is a non-catchable and non-ignorable signal that forces the process to terminate immediately without allowing it to clean up resources or perform any shut down tasks. This means the process doesn't have the opportunity to close files, release memory, or notify other processes of its termination, resulting in an abrupt stop. The use of the -9 option is specifically intended for situations where a process is unresponsive to other termination requests or needs to be killed without delay.

This is distinct from other types of termination signals that might allow for graceful shutdowns or pauses. For instance, sending a different signal like SIGTERM (using 'kill PID') would allow the process to handle the termination request and potentially perform cleanup actions before exiting. Thus, the nature of the SIGKILL signal makes invoking 'kill -9 PID' the most definitive way to stop a process immediately.