I'm trying out Ubuntu 11.10 (Oneiric Ocelot) on a PC with a Mac keyboard attached. I made a few hacks to make the keyboard work smoothly and in a (very roughly) Mac-like fashion. I figured I'd make a few notes here for my own future reference. (Note: I'm using a U.S. keyboard. If you are using a different kind of keyboard, your mileage may vary.)

Goals

1. Make the function keys (F1..F12) work as function keys without needing to hold down the Fn key.
2. Use Mac-like keyboard shortcuts for window navigation (Cmd-Tab, Cmd-`) and the terminal (Cmd-C for copy, Cmd-V for paste).
3. Avoid stepping on Unity's use of the Super key (i.e. the command key on Macs and the Windows key on PC keyboards).
4. Use the legacy Caps Lock key for something useful.

The plan

1. Change a driver parameter to enable use of the function keys without holding down the Fn key.
2. By default, the keyboard's left and right command keys are mapped to Super_L and Super_R. Map these instead to the seldom-used Hyper_L and Hyper_R keysyms. (If you try to use the Super keys for shortcuts, the Unity dock will appear every time you hold down the command key. It's really annoying.)
3. Map the Caps Lock key to Super_L so it can be used for certain Unity shortcuts.

Making function keys work

Create a file in /etc/modprobe.d which sets the fnmode parameter of the hid_apple driver to 2 = fkeysfirst:

echo 'options hid_apple fnmode=2' > /etc/modprobe.d/apple_kbd.conf

Reboot, and the function keys will work without needing to hold down the Fn key. (You can access the volume controls and such by holding down the Fn key.) Thanks to Alan Doyle for reporting on this tweak.

Remapping the keys

I used the xkbcomp utility to remap the keys. I extracted the current keyboard mappings into a default.xkb file, made a copy of the mapping file as mackeyboard.xkb, made the changes to this file, then loaded the new mapping into the running X server:

xkbcomp :0 default.xkb
cp default.xkb mackeyboard.xkb
vi mackeyboard.xkb
xkbcomp mackeyboard.xkb :0

I'm attaching my mackeyboard.xkb file and the diff for reference. (Use these at your own peril.) I made the following changes:

1. Changed the LWIN and RWIN keycode identifiers to LCMD and RCMD, for clarity.
2. Commented out the LMTA and RMTA keycode aliases, to avoid confusion.
3. Changed the CAPS keysym mapping from Caps_Lock to Super_L.
4. Changed the LWIN and RWIN (now LCMD and RCMD) keysym mappings from Super_L and Super_R to Hyper_L and Hyper_R.
5. Changed the modifier mapping so that only the CAPS keycode is used for Mod4. Since Mod3 wasn't previously in use, I mapped Hyper_L and Hyper_R to this modifier.

Configuring new shortcuts

In System Settings -> Keyboard -> Shortcuts, configure these shortcuts:

Section	Shortcut name	Key
Navigation	Switch applications	Cmd+Tab
Navigation	Switch windows of an application	Cmd+`
Windows	Toggle fullscreen mode	Cmd+Return
Windows	Close Window	Cmd+Q

In Terminal's Edit -> Keyboard Shortcuts, configure these shortcuts:

Section	Shortcut name	Key
File	New Window	Cmd+N
File	Close Window	Cmd+W
Edit	Copy	Cmd+C
Edit	Paste	Cmd+V
View	Zoom In	Cmd+=
View	Zoom Out	Cmd+-
View	Normal Size	Cmd+0

I think the biggest benefit of the new Terminal shortcuts is the use of sensible copy and paste shortcuts that don't interfere with using Ctrl-C and Ctrl-V in the shell.

Future hacks

The following improvements are left as an exercise for the reader:

• Have xkbdcomp load the new mapping every time you log in, so you don't have to run it manually.
• Make other applications (such as Google Chrome) recognize Mac shortcuts such as Cmd-C and Cmd-V.
• Figure out a generic way for specifying key translations for specific apps that happen to be in the foreground, similar to the functionality that AutoHotkey provides for Windows. (compiz plugin? resurrect the deprecated XEvIE X11 extension?)

Update, November 7, 2011: AutoKey

In the comments, Nivth Ket brought to my attention the AutoKey tool for mapping arbitrary keys to other keys, phrases, or even Python scripts. This tool seems to use the XRecord extension to X11 to listen to incoming keys. I gave AutoKey 0.80.3 a test drive, and found a few limitations that clashed with my needs. However, with a few hacks, I think I've overcome these limitations and found a solution that seems to work for me so far. The limitations and workarounds are as follows:

• The AutoKey GUI does not allow assigning the same hotkey to multiple actions. This prevents me from assigning a key combination to do one thing in a particular application (i.e. the window title matches "Google Chrome"), and something else in every other application. The workaround is to edit the configuration files in ~/.config/autokey/data directly.
• AutoKey does not have a notion of order semantics for the entries — the entries are processed in a seemingly random order. Therefore, if my entry for "Cmd-V with no window filter" happens to come before my entry for "Cmd-V only for Terminal windows", the former will eclipse the latter, and the Terminal-only rule will never happen. My workaround was to hack AutoKey to always process entries with filters first, then process entries with no filters. Here is the patch.
• AutoKey does not support the little-known "Hyper" modifier key, which I use in my layout for the "command" keys. My workaround was to hack AutoKey to support the Hyper modifier. Here is the patch.

Downloads

• mackeyboard.xkb - The xkb file for my keyboard, suitable for loading into a running X server with xkbcomp.
• mackeyboard.diff - The changes I made to the original keyboard mappings.