Kill, Pkill and Killall

The kill command sends the specified signal such as kill process to the specified process or process groups. If no signal is specified, the TERM signal is sent. kill command can be internal as part of modern shells built-in function or external located at /bin/kill. For the signals, either the signal name or signal number can be used. If a Linux or Unix process is running a program, a process identification number (PID) is automatically assigned to each process when it is created on the system. PID for the process needs to be looked up and given as an argument to kill.