Chapter 6. Your X Environment

An important piece to the X Window System puzzle is filled by the xmodmap client. When the user performs any action -- such as typing a key or moving the mouse -- the server sends a packet of information to the client called an event. These events are then translated into actions by the client. You can use the xmodmap utility to effectively change the event that is reported to the client.

You can use the xmodmap client to reassign key codes within the keymap table. xmodmap can therefore be used to redefine how the key is interpreted by the client. You probably wouldn't want to translate the alphanumeric keys on the keyboard, but you may want to translate others. For example, you might want to change the BACKSPACE key to DELETE:

% xmodmap -e "keysym BackSpace = Delete"

% xmodmap -e "keysym Caps_Lock = "

effectively disabling the CAPS LOCK key entirely. Note that the symbol is now gone and can't be redefined without using the hardware key code.

If it ever seems that keystrokes are not working correctly, you can check current keysym settings by running xmodmap with the -pk argument. Use the xev client to determine exactly which key code a key generates on your display. There is also a public domain client called xkeycaps that can be used to display the keysyms for selected keyboards.

You can use xmodmap to add or remove keysyms, or even to redefine the key code associated with that keysym. You can also use it to redefine the mouse buttons, using the pointer keyword. For example, to have the second and third mouse button switch places, you can enter:

% xmodmap -e "pointer = 1 3 2"

If you have a large number of keys to remap, you can put the commands in a file that is read when your X session starts. For example, create a file called .Xmodmap:

! my .Xmodmap file
remove Lock = Caps_Lock
remove Control = Control_L
keysym Control_L = Caps_Lock
keysym Caps_Lock = Control_L
add Lock = Caps_Lock
add Control = Control_L
  ...

  ...
xset b 10 100 10
xrdb $HOME/.Xdefaults
xmodmap $HOME/.Xmodmap
fvwm &
  ...

Alternately, you might want to assign different functions to little-used keys, such as making the tiny "enter" key on Powerbook keyboards into another command key. Remember, too, that some keys may have different names than what you're used to. Sun keyboards, for example, often come with a "meta" key; Macintosh keyboards have an "option" key where PC users expect to find "alt" (though they act the same); and so forth.

keycode  54 = Shift
keycode  56 = Alt
keycode  57 = space
        control keycode  57 = nul
keycode  58 = Control
keycode  86 = less             greater          bar
keycode  97 = Control

--LM, EP, and SJC