Linux Kill Process: Stop Processes by PID or Name

When a Linux app freezes or a background command stops responding, closing the window is not always enough. The process can keep running, hold files open, or block you from starting the program again.

Linux gives you several ways to stop it manually. Use kill when you know the process ID (PID), killall when you know the exact process name, and pkill when you want to match a name, user, or command pattern.

This guide explains how to kill a process in Linux by PID or name, how signals work, and when to use SIGTERM or SIGKILL.

Regular users can terminate only their own processes. The root user, or a user running commands with sudo, can terminate processes system-wide. The commands shown here work on any Linux distribution.

Quick Reference #

For a printable quick reference, see the kill cheatsheet .

Understanding Kill Signals #

kill, killall, and pkill send a given signal to specified processes or process groups. If no signal is specified, they default to 15 (TERM) for a graceful shutdown.

Common signals include:

• 1 (HUP) - Reload configuration for daemons that support it.
• 9 (KILL) - Force immediate termination. Use it as a last resort.
• 15 (TERM) - Gracefully stop a process. This is the default signal.

Signals can be specified in three different ways:

• Using a number, such as -1
• With the SIG prefix, such as -SIGHUP
• Without the SIG prefix, such as -HUP

Use the -l option to list all available signals:

kill -l  # or killall -l

Using the kill Command #

To terminate a process with the kill command, you first need to find its PID. You can do this using different commands, such as top, ps , pidof, and pgrep .

For example, use ps to search for a running Firefox process:

ps aux | grep firefox

If Firefox has become unresponsive, find its process IDs with the pidof command:

pidof firefox

The command prints all matching Firefox PIDs:

2551 2514 1963 1856 1771

Start with the default TERM signal so the process has a chance to exit cleanly:

kill 2551 2514 1963 1856 1771

If the process ignores TERM, send the KILL signal:

kill -9 2551 2514 1963 1856 1771

SIGKILL cannot be caught or ignored, so it stops the process immediately. Use it only when the normal kill PID command does not work.

Using the killall Command #

The killall command terminates all processes matching a given name. This is useful when a program has multiple running instances and you do not want to copy several PIDs.

Using the same scenario as before, send SIGTERM to all Firefox processes:

killall firefox

If Firefox still does not close, force it to stop:

killall -9 firefox

killall accepts several options, such as sending signals to processes owned by a specific user, matching process names against regular expressions, and filtering by process age. You can get a list of all options by typing killall --help in your terminal.

For example, to terminate Firefox processes owned by the user zoe, run:

sudo killall -u zoe firefox

Using the pkill Command #

pkill terminates processes that match the pattern given on the command line:

pkill firefox

The process name does not have to be an exact match. Partial matches work too, which makes pkill flexible but also easier to misuse.

Before using a broad pattern, preview the matches with pgrep :

pgrep -a firefox

To kill only Firefox processes owned by the user zoe, run:

pkill -u zoe firefox

If the process does not stop, add -9:

pkill -9 -u zoe firefox

Using xkill for GUI Applications #

If a graphical application becomes unresponsive, you can use xkill to terminate it by clicking on its window:

xkill

After running the command, your cursor changes to an “X”. Click on the window you want to close, and the application will be terminated.

Troubleshooting #

Process will not die with -9
If a process does not terminate even with SIGKILL (-9), it may be a zombie process. Zombie processes are already dead but still appear in the process table because their parent has not read their exit status.

To find zombie processes:

ps aux | awk '$8 ~ /Z/'

You cannot kill a zombie directly. Instead, kill its parent process or restart the system.

Permission denied
If you get a “Permission denied” error, the process belongs to another user. Use sudo to terminate it:

sudo kill PID

If the process still does not stop, use sudo kill -9 PID.

Conclusion #

To kill a process in Linux, use kill PID when you know the process ID, killall name for an exact process name, or pkill pattern when you need flexible matching. Start with the default SIGTERM signal, then use SIGKILL only when the process refuses to exit.

About the authors

Dejan Panovski

Dejan Panovski is the founder of Linuxize, an RHCSA-certified Linux system administrator and DevOps engineer based in Skopje, Macedonia. Author of 800+ Linux tutorials with 20+ years of experience turning complex Linux tasks into clear, reliable guides.

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