xmodmap

xmodmap is a utility for modifying keymaps and pointer button mappings in Xorg. It allows users to customize how their keyboard and mouse interact with the operating system by reassigning keys, creating new key combinations, or changing the behavior of mouse buttons.

The primary function of xmodmap is to read and write keymap tables. These tables define which keysym (a symbolic name for a key or a combination of keys and modifiers) is produced when a particular keycode (a numerical identifier for a physical key press) is detected. Users can create custom configuration files, often named .Xmodmap in their home directory, to specify these remappings.

For example, a user might use xmodmap to swap the Caps Lock and Control keys, making Caps Lock act as Control and vice versa. This is a common customization for programmers or users who frequently use modifier keys. Similarly, a user could remap a less-used key to perform a specific function or character.

xmodmap can also be used to alter the behavior of mouse buttons. This might include inverting the scroll wheel direction or reassigning the function of different mouse buttons.

To apply changes, users typically run the xmodmap command with their configuration file as an argument, for instance, xmodmap ~/.Xmodmap. The changes made by xmodmap are usually applied to the current X session and may need to be reapplied after logging out or restarting the graphical environment. While powerful, xmodmap has largely been superseded by more modern input configuration methods in many desktop environments, though it remains a valuable tool for fine-grained control.