Ubuntu – Reassigning modifier keys with xkb

does somebody have good instructions for how the modifier keys can be changed in xkb (via placing the modified xkb file in /usr/share/X11/xkb).

To explain: I'm able to make the layout I want in xmodmap. This is the standard US layout (for laptops), but with the modifier keys swapped round (the usual ctrl vs. capslock; alt vs. windows etc, see below). However, when I output this layout with xkbcomp the resulting keyboard layout seems to be incomplete (and has errors too): I.e. rebooting and reloading that layout isn't the same as running xmodmap again. Not sure why that is – but I reckon the simplest might be just writing this from scratch for xkb (rather than going via xmodmap -> xkb).

So – does anybody have clear instructions on how you can reassign the modifier keys in an xkb file? I basically want to take the US layout, and do the following swaps:

• capslock –> hyper
• (shift)
• ctrl –> super
• (fn)
• windows –> alt/meta
• alt –> control
• (space)
• altgr –> control
• ctrl –> hyper
• (arrow left)

In this list, the first label is meant to be the physical key on the laptop (going anti-clockwise from capslock towards the arrow keys); unmodified keys shown in (…); the second label is the desired function.

What I'd like to produce is the actual xkb file (i.e. US + those modifiers), that I can then place in /usr/share/X11/xkb and link from /usr/share/X11/xkb/rules/evdev.xml, so that I can simply swap to this layout when needed.

(The reason I want to do this in xkb and not in xmodmap is because xkb can deal with different layouts in different windows, and I've not found a way of doing that with xmodmap, which always seems to be systems wide.)

PS. In xmodmap this would be:

clear control
clear lock
clear mod1
clear mod2
clear mod3
clear mod4
clear mod5

! 66/CapsLk
! Shift
! 37/Ctrl - Fn - 133/Win - 64/Alt - Space - 108/AltGr - 105/Ctrl

keycode  66 = Hyper_L Hyper_L Hyper_L Hyper_L
keycode  37 = Super_L Super_L Super_L Super_L
keycode 133 = Alt_L Alt_L Alt_L Alt_L
keycode  64 = Control_L Control_L Control_L Control_L
keycode 108 = Control_R Control_R Control_R Control_R
keycode 105 = Hyper_R Hyper_R Hyper_R Hyper_R

add control = Control_L Control_R
add mod1 = Alt_R Alt_L
add mod2 = Num_Lock
add mod3 = Hyper_L Hyper_R
add mod4 = Super_L

So how do I achieve the same in xkb?

PPS. I am also confused about Alt vs. Meta – could somebody explain the significance wrt. xkb? (Or Ubuntu in general?) I had assumed that alt=meta (in emacs) but there seems to be a difference. What is it?

Edit. Having looked into this some more, I assume my xkb file (to go into /usr/share/X11/xkb/symbols) would look something like this:

partial alphanumeric_keys modifier_keys
xkb_symbols "basic" {

    include "us(basic)"
    name[Group1]= "enHT (English, US, Hyper-Terminal)";

    key <CAPS> { [ Hyper_L, Hyper_L ] };
// Map Ctrl to the left Alt key, Alt to the left Win key,
// and Super to the left Ctrl key.
    replace key <LALT> { [ Control_L, Control_L ] };
    replace key <LWIN> { [ Alt_L, Meta_L ] };
    replace key <LCTL> { [ Super_L ] };
    modifier_map Mod1    { <LWIN> };
    modifier_map Mod4    { <LCTL> };
    modifier_map Mod5    { <CAPS> };
    modifier_map Control { <LALT> };

};

However, the instructions in the file dont seem to work (even regarding the general US keyboard layout included). So probably something basic is wrong.