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

How to Terminate a Linux Process

If a process runs in the foreground you can stop it with Ctrl+C. For background or invisible processes use dedicated commands.

kill command

The kill command terminates a process by its PID. Syntax:

kill <signal> <PID>

signal

is the termination signal, PID is the process ID.

Common termination signals

SIGHUP (1) : Hangup – sent when the controlling terminal is closed.

SIGINT (2) : Interrupt – sent when the user terminates the process (e.g., Ctrl+C).

SIGKILL (9) : Kill – forces immediate termination, cannot be caught.

SIGTERM (15) : Terminate – polite request to exit; can be ignored but is preferred.

SIGSTOP (19) : Stop – pauses the process, can be resumed later.

Obtaining a Process PID

Use pidof to get the PID from the process name: pidof exact_process_name Example for Java processes:

pidof java
8075 1032

Using kill

To terminate a process, provide its PID and optionally a signal. If no signal is given, kill defaults to SIGTERM (15).

# Start a background sleep process
sleep 120 &
[1] 125686

# Terminate it
kill 125686
[1]+  terminated  sleep 120

You can also specify the signal by name or number, e.g., kill -SIGKILL 125746 or kill -9 125759.

killall command

If you do not know the PID or want to kill all instances of a process, use killall: killall [signal] <process-name> Without a signal, killall sends SIGTERM (15) by default.

# Kill all sleep processes
sleep 120 &
[1] 112351
sleep 2000 &
[2] 112362
killall sleep
[1]-  Terminated  sleep 120
[2]+  Terminated  sleep 2000

pkill command

pkill

is a pattern‑matching alternative to killall. It can filter by user ( -u), exact match ( -x), or signal ( -signal). pkill [options] pattern Example to stop all nginx processes:

pkill nginx