Master Linux Process Termination: kill, killall, and pkill Explained

Linux Process Termination Signals

When a process is stopped by the operating system or a user, a termination signal is sent. Common signals include SIGTERM (15) for graceful shutdown and SIGKILL (9) for forced termination.

Getting a Process PID

To kill a process you need its PID. You can retrieve it by name using: pidof exact_process_name For example, to find the PID of a Java process: pidof java Output may show multiple PIDs, e.g., 8075 1032.

Using the kill Command

The kill command requires the PID and optionally a signal: kill [signal] <PID> If no signal is specified, kill defaults to SIGTERM (15). Example of killing a background sleep job:

$ sleep 120 &
[1] 125686
$ kill 125686
[1]+  terminated  sleep 120

You can also specify the signal by name or number:

$ kill -SIGKILL 125746
$ kill -9 125759

Using the killall Command

If you don’t know the PID or want to terminate a process and all its children, use killall: killall [signal] <process-name> Without a signal, killall sends SIGTERM (15). Example killing all sleep processes:

$ sleep 120 &
[1] 112351
$ sleep 2000 &
[2] 112362
$ killall sleep
[1]-  Terminated  sleep 120
[2]+  Terminated  sleep 2000

Using the pkill Command

pkill

combines pgrep pattern matching with kill: pkill [options] pattern Useful options include: -u: match processes owned by a specific user -x: exact match of the process name -signal: specify termination signal (default SIGTERM)

Example terminating all nginx processes: pkill nginx These commands provide flexible ways to manage and terminate Linux processes safely and efficiently.