You can define your own keymappings in the X Windowing System using xmodmap. Usually your system should read the ~/.Xmodmap file automatically, so you can just put things there. Sometimes the stuff also goes into your ~/.xmodmaprc file.
Some more modern systems require Xkb instead, but you can convert your old .xmodmap files without much hassle. Googleize “xmodmap to xkb cookbook.”
On my system (Debian), I have a ~/.xsession file that contains this:
... xmodmap .xmodmaprc x-window-manager
This will read the .xmodmaprc file before starting the window manager. (In my case, x-window-manager eventually resolves to wmaker.) Basically, the format of the file is very complex. You can have .xmodmap highlighted in Emacs with XModMapMode.
We will ignore the symbolic names of keys for the beginning. All we need to know is that every keyboard sends a certain keycode, which is then interpreted by X. X will then produce a symbolic representation of the key (and modifier keys) pressed.
Note that these files are also set up for use with the DvorakKeyboard, which is another great ergonomic “hack”. However, you can adapt the examples for your need.
Assume we want to switch the Y and the Z key.
First we need to determine the keycodes of the two keys we want to switch. We use the xev program to determine those. Start it, then press the two keys, take a look at the (verbose) output:
KeyPress event, serial 27, synthetic NO, window 0x3400001, root 0x26, subw 0x0, time 4047624180, (170,-12), root:(365,516), state 0x0, '''keycode 52''' (keysym 0x79, y), same_screen YES, XLookupString gives 1 characters: "y" ... KeyPress event, serial 27, synthetic NO, window 0x3400001, root 0x26, subw 0x0, time 4047625057, (170,-12), root:(365,516), state 0x0, '''keycode 29''' (keysym 0x7a, z), same_screen YES, XLookupString gives 1 characters: "z" ...
So we add to our file:
keycode 52 = z Z keycode 29 = y Y
Run xmodmap with the file, and test it with xev. Should have worked.
‘Z’ are the symbolic identifiers used by X, also called keysyms. The keysyms are listed in /usr/include/X11/keysymdef.h or thereabouts. If you want to use them, do not use the XK_ prefix.
On most system, there is a Mode_switch key. It acts like a Shift key. Therefore you can assign four meanings to every key: key, Shift+key, Mode_switch+key, and Shift+Mode_switch+key. Usually the Mode_switch key is used on non-US keyboards for a few selected keys only. It is labelled AltGr.
One very simple change to make AltGr+c produce a `ç’ (if you don’t want to type `C-x 8 , c’ to produce it):
! C cedille keycode 54 = c C ccedilla Ccedilla
Some systems use AltGr+c for the cent sign and AltGr C for the copyright sign.
Modifiers are extras that get interpreted by the applications themselves. X can only translate certain keycodes to certain modifiers. What then happens, however, is up to the Window Manager and the Application.
Some people have Ctrl, Alt, Meta and “Win” keys. X knows the Ctrl, Alt, Meta, Hyper and Super modifiers, as well as the corresponding keysym. What people usually want, is to change their Alt, Meta and “Win” keys to a new keysym and matching modifier. See MetaKeyProblems for more.
Here is a simple example. I want one of my Alt keys to have the Meta keysym, and to produce the Meta modifier. My other Alt key should be the Mode_switch. So first I take the Meta modifier away from all other keys (Meta is called mod1 by X), then I map the keycodes to the keysyms, and I add the modifier to one of them.
clear mod1 keycode 64 = Meta_L keycode 113 = Mode_switch add mod1 = Meta_L
Now the key producing the keycode 64 has keysym Meta_L and the mod1 modifier. The key producing the keycode 113 has keysym Mode_switch and no modifier.
Note that to get it to work in gnome, you need to use .gnomerc (i think) viz. Put something like ‘xmodmap .xmodmap’ in your ~/.gnomerc. This .gnomerc stuff seems to be not what the docs for gdm etc. say, but is the only way i could get it to work for gnome. – DeepakGoel
See also: xmodmap man page, XModMapMode.