Xmodmap

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.

xkeycaps provides a graphical front-end to xmodmap, you can install it from the official repositories.

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.

Tip: There are predefined descriptive keycodes that make mapping additional keys easier (e.g. XF86AudioMute, XF86Mail). Those keycodes can be found in: /usr/include/X11/XF86keysym.h

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 [ -s ~/.Xmodmap ]; then
    xmodmap ~/.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.

Accents on US keyboards

The following is an example configuration:

AltGr + e -> é
AltGr + r -> è
AltGr + a -> à
AltGr + u -> ù
AltGr + i -> ì
AltGr + o -> ò
AltGr + c -> ç
AltGr + [ -> «
AltGr + ] -> »
AltGr + ; -> dead diaresis (ï, ü, etc.)
AltGr + 6 -> dead circumflex (î, ê, etc.) 

This is an xmodmap file which remaps keys to match the above example.

clear Mod1
clear Mod2
!  us.map with a few redefinitions
keycode   9 = Escape Escape
keycode  10 = 1 exclam
keycode  11 = 2 at at
keycode  12 = 3 numbersign
keycode  13 = 4 dollar dollar
keycode  14 = 5 percent currency
keycode  15 = 6 asciicircum dead_circumflex
keycode  16 = 7 ampersand braceleft
keycode  17 = 8 asterisk bracketleft
keycode  18 = 9 parenleft bracketright
keycode  19 = 0 parenright braceright
keycode  20 = minus underscore backslash
keycode  21 = equal plus
keycode  22 = BackSpace Delete
keycode  23 = Tab Tab
keycode  24 = q
keycode  25 = w
keycode  26 = e E eacute
keycode  27 = r R egrave
keycode  28 = t
keycode  29 = y
keycode  30 = u U ugrave
keycode  31 = i I igrave
keycode  32 = o O ograve
keycode  33 = p
keycode  34 = bracketleft braceleft guillemotleft
keycode  35 = bracketright braceright guillemotright
keycode  36 = Return
keycode  37 = Control_L
keycode  38 = a A agrave
keycode  39 = s
keycode  40 = d
keycode  41 = f
keycode  42 = g
keycode  43 = h
keycode  44 = j
keycode  45 = k
keycode  46 = l
keycode  47 = semicolon colon dead_diaeresis
keycode  48 = apostrophe quotedbl
keycode  49 = grave asciitilde dead_grave
keycode  50 = Shift_L
keycode  51 = backslash bar
keycode  52 = z
keycode  53 = x
keycode  54 = c C ccedilla
keycode  55 = v
keycode  56 = b
keycode  57 = n
keycode  58 = m
keycode  59 = comma less apostrophe
keycode  60 = period greater quotedbl
keycode  61 = slash question
keycode  62 = Shift_R
keycode  63 = KP_Multiply
keycode  64 = Alt_L Meta_L
keycode  65 = space space
keycode  66 = Caps_Lock
keycode  67 = F1 F11
keycode  68 = F2 F12
keycode  69 = F3 F13
keycode  70 = F4 F14
keycode  71 = F5 F15
keycode  72 = F6 F16
keycode  73 = F7 F17
keycode  74 = F8 F18
keycode  75 = F9 F19
keycode  76 = F10 F20
keycode  77 = Num_Lock
keycode  78 = Scroll_Lock
keycode  79 = KP_7
keycode  80 = KP_8
keycode  81 = KP_9
keycode  82 = KP_Subtract
keycode  83 = KP_4
keycode  84 = KP_5
keycode  85 = KP_6
keycode  86 = KP_Add
keycode  87 = KP_1
keycode  88 = KP_2
keycode  89 = KP_3
keycode  90 = KP_0
keycode  94 = less greater bar
keycode  95 = F11 F11
keycode  96 = F12 F12
keycode 108 = KP_Enter
keycode 109 = Control_R
keycode 112 = KP_Divide
keycode 113 = Mode_switch
keycode 114 = Break
keycode 110 = Find
keycode  98 = Up
keycode  99 = Prior
keycode 100 = Left
keycode 102 = Right
keycode 115 = Select
keycode 104 = Down
keycode 105 = Next
keycode 106 = Insert
keycode 116 = Mode_switch
! right windows-menu key, redefined as Compose key
keycode 117 = Multi_key
add Mod1 = Alt_L
add Mod2 = Mode_switch

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