Difference between revisions of "Xmodmap"

Revision as of 21:03, 29 January 2013

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Xmodmap is a utility for modifying keymaps and pointer button mappings in Xorg.

Introduction

The Linux kernel generates a code each time a key is pressed on a keyboard. That code is compared to a table of keycodes defining a figure that is then displayed.

This process is complicated by Xorg, which starts its own table of keycodes. Each keycode can belong to a keysym. A keysym is like a function, started by typing a key. Xmodmap allows you to edit these keycode-keysym relations.

Keymap table

Print the current keymap table formatted into expressions:

$ xmodmap -pke

keycode  57 = n N

Each keymap is followed by the keysyms it is mapped to. The above example indicates that the keycode 57 is mapped to the lowercase n, while the uppercase N is mapped to keycode 57 and Shift.

Each keysym column in the table corresponds to a particular key combination:

1. Template:Keypress
2. Template:Keypress
3. Template:Keypress
4. Template:Keypress
5. Template:Keypress
6. Template:Keypress

Not all keysyms have to be set, but if you want to assign a latter keysym without assigning earlier ones set them to NoSymbol.

You can check which keymap corresponds to a key on your keyboard with xev.

Custom table

You can create your own map and store it in your home directory (i.e. ~/.Xmodmap). Print the current keymap table into a configuration file:

xmodmap -pke > ~/.Xmodmap

Make the desired changes to ~/.Xmodmap and then test the new configuration with:

xmodmap ~/.Xmodmap

To activate your custom table when starting Xorg add the following:

~/.xinitrc

if [ -f $HOME/.Xmodmap ]; then
    /usr/bin/xmodmap $HOME/.Xmodmap
fi

Alternatively, edit the global startup script /etc/X11/xinit/xinitrc.

Test changes

You can also make temporary changes for the current session. For example:

xmodmap -e "keycode  46 = l L l L lstroke Lstroke lstroke"
xmodmap -e "keysym a = e E"

Special keys/signals

You can also also edit the keys: Template:Keypress, Template:Keypress, Template:Keypress and Template:Keypress (there always exists a left and a right one (Alt_R=AltGr)).

For example this can be useful if your right Control key is not working like your left one but you would like it to.

At first you have to delete/clear the signals that should be edited. In the beginning of your ~/.Xmodmap:

!clear Shift
!clear Lock
clear Control
!clear Mod1
!clear Mod2
!clear Mod3
clear Mod4
!clear Mod5
keycode   8 =
...

Remember, ! is a comment so only Template:Keypress and Template:Keypress (Standard: Super_L Super_R) get cleared.

Write the new signals at the end of ~/.Xmodmap

keycode 255 =
!add Shift   = Shift_L Shift_R
!add Lock    = Caps_Lock
add Control = Super_L Super_R
!add Mod1    = Alt_L Alt_R
!add Mod2    = Mode_switch
!add Mod3    =
add Mod4    = Control_L Control_R
!add Mod5    =

The Template:Keypress keys have now been exchanged with the Template:Keypress keys.

If you get the following error message X Error of failed request: BadValue (integer parameter out of range for operation) it means the key you are trying to add is already in another modifier, so remove it using "remove MODIFIERNAME = KEYSYMNAME". Running xmodmap gives you a list of modifiers and keys that are assigned to them.

Reverse Scrolling

The natural scrolling feature available in OS X Lion can be mimicked with xmodmap. Since the synaptics driver uses the buttons 4/5/6/7 for up/down/left/right scrolling, you simply need to swap the order of how the buttons are declared in ~/.Xmodmap.

Open ~/.Xmodmap and append the following line to the file:

pointer = 1 2 3 5 4 7 6 8 9 10 11 12

Note how the 4 and 5 have been reversed.

Then update xmodmap:

xmodmap ~/.Xmodmap

To return to regular scrolling simply reverse the order of the 4 and 5 or delete the line altogether. For more information check Peter Hutterer's post, Natural scrolling in the synaptics driver, or the Reverse scrolling direction ala Mac OS X Lion? forum thread.

Additional resources

• Current man page at X.Org Foundation
• Multimediakeys with .Xmodmap HOWTO by Christian Weiske
• Mapping unsupported keys with xmodmap by Pascal Bleser
• Multimedia Keys article on the Gentoo Wiki
• How to retrieve scancodes by Marvin Raaijmakers
• List of Keysyms Recognised by Xmodmap on LinuxQuestions