Mastering Linux killall: How to Safely Terminate Processes with Advanced Options

Linux's command line offers many commands to kill processes.

For example, you can pass a PID to the kill command, or use pkill with a regular expression to terminate matching processes.

The killall command, by default, matches the exact name of the process and kills it.

Linux killall command

The killall command can send a signal to a specific process. By default the signal is SIGTERM, but other signals can be specified with options.

Below are practical examples of using this command.

1. Basic example

Assume there are two processes whose names start with the same characters.

How to kill the test_again process?

As shown, killall terminates test_again. You can verify with ps:

The test_again process no longer appears because it has been killed.

2. Using the -I option to ignore case

By default, killall is case‑sensitive. For example:

The command cannot find a process named TEST, but the test process is running.

To make killall ignore case, use the -I option (capital i):

Now the test process is successfully terminated.

3. Using the -i option for interactive termination killall can terminate multiple processes.

To terminate processes interactively, use the -i option. Example:

This allows the user to confirm each termination when multiple processes are targeted.

4. Using the -q option to suppress output

When killall cannot find the specified process, it prints an error message.

To run killall quietly, use the -q option:

After applying -q, the command's output is suppressed.

5. Using the -l option to list all supported signals

You can send a specific signal with -s followed by the signal name.

To see all available signals, use the -l (lowercase L) option:

killall

supports all of these signals.

A fun little question

The man page for killall states that if a process name is 15 characters or fewer, it matches the full name by default.

Consider two processes with long names:

The first process name has exactly 15 characters. Using killall successfully kills it:

If both process names exceed 15 characters, killall will kill both according to the man page. Example:

When attempting to kill the second long‑named process, only the specified one is terminated:

Version information of the killall command used in the experiment:

Can you guess why this issue occurs? Feel free to leave a comment below.