... Sometimes a background process or a process without a controlling terminal hangs up and you will need to destroy this process by killing it. To kill a process use the kill command. kill [-signal] process_identifier (PID) . ... Always try to kill a process with a simple kill command. kill process_identifier . ... If this does not work use the -1 (one) signal. kill -1 process_identifier . ... As a last resort use the -9 signal: kill -9 process_identifier . ... Using the shell built-in kill command . ...