xkill

xkill is a command-line utility for the X Window System that allows users to kill X client processes by interacting with their windows. When xkill is invoked, the cursor typically changes to a skull or crosshairs icon. The user then clicks on the window of the application they wish to terminate. Once clicked, xkill sends a kill signal to the X client associated with that window, usually causing the application to close.

This tool is useful for situations where an application has become unresponsive or is behaving erratically and cannot be closed through normal means. It provides a direct method to forcefully terminate such processes without needing to know their process ID (PID). To use xkill, a user typically opens a terminal and types the command xkill. After the cursor changes, they simply select the target window.

While convenient, xkill should be used with caution. Killing an application by clicking its window does not allow the application to perform any cleanup operations, such as saving unsaved data. Therefore, it is generally recommended to attempt to close applications gracefully first before resorting to xkill. In some desktop environments, there may be graphical alternatives or keyboard shortcuts that achieve a similar effect, but xkill remains a fundamental and widely available tool for X users.