Master Linux Process Management: How to Use kill, pkill, and killall Effectively

Kill Command and Signals

When a Linux (or macOS) application becomes unresponsive, you can force it to exit by sending a signal with the kill command. Linux defines about 60 signals, but the most commonly used are SIGTERM (signal 15) and SIGKILL (signal 9).

kill -l

The command above lists all available signals.

SIGTERM – Requests graceful termination; the process can catch or ignore it and perform cleanup.

SIGKILL – Forces immediate termination; the process cannot ignore it and any unsaved data is lost.

Using kill

The basic syntax is:

kill [signal] PID(s)

If no signal is specified, SIGTERM is used by default. To force termination you can run:

kill SIGKILL 1234

or the shorthand:

kill -9 1234

Finding Process IDs

If you do not know the PID, list running processes with:

ps ux

This displays each process together with its PID.

Killing Multiple Processes

You can terminate several processes in one command by providing multiple PIDs:

kill -9 1111 2222 3333

Using pkill

pkill

allows you to kill processes by name, supporting regular expressions. For example, to stop Firefox you can run:

pkill firefox

Partial matches also work:

pkill fire

To avoid accidental termination, first list matching processes with:

pgrep -l firefox

Using killall

killall

kills all processes that share the same name. To close every Firefox instance:

killall firefox

It can also be used to restart desktop components, e.g.:

killall nautilus

Graphical Kill with xkill

Running xkill changes the cursor to a cross; clicking the misbehaving window immediately terminates its process. You can bind this command to a keyboard shortcut for quick access.

Conclusion

Instead of rebooting when an application hangs, the various kill commands let you safely terminate problematic processes, preventing system crashes and downtime—especially valuable on servers where a single rogue process could cause outages.