How to Kill an Unresponsive Program in Linux Using the killall Command

If you are running a graphical application on Linux—like the Firefox web browser or a heavy text editor—and it completely freezes, clicking the “X” button in the corner of the window often does absolutely nothing. The graphical interface is locked, but the underlying software process is still hoarding your CPU and RAM in the background.

To forcefully terminate the software and reclaim your system resources, you must use the command line. While the standard kill command requires you to hunt down the specific numerical Process ID (PID) of the frozen software, the killall command is far more intuitive, allowing you to execute the software using its human-readable name.

How to Use the killall Command

The killall utility is part of the psmisc package, which is pre-installed on virtually all modern Linux distributions (Ubuntu, Debian, Fedora, Arch).

1. Open your Linux terminal (if your entire desktop environment is frozen, press Ctrl + Alt + F3 to drop into a raw TTY console).
2. Type the command killall followed by a space, and then the exact, case-sensitive name of the application that is frozen.

   killall firefox

3. Press Enter.

Unlike the standard kill command which only targets one specific thread, killall aggressively hunts down every single active instance of the program across the entire operating system and terminates them all simultaneously. The frozen window on your desktop will vanish instantly.

How to Force an Absolute Kill (SIGKILL)

By default, killall sends a polite “SIGTERM” (Signal 15) request to the application, asking it to please shut down and save its data. However, if a program is severely hung in an infinite loop, it might ignore this polite request entirely.

To forcefully terminate the application at the kernel level—giving the software zero opportunity to save its data or resist—you must append the -9 flag to issue a SIGKILL (Signal 9).

1. In your terminal, execute the following command:

   killall -9 firefox

The Linux kernel will instantly rip the application out of the system memory, forcefully resolving the freeze.