Note: I posted this elsewhere on the 'net some time ago, but I'm putting it here to make it easier for me to find…
So, I am currently running Ubuntu 10.10 (just installed last night), and have the ability to both use unicode entry with the Ctrl+Shift+U sequence, as well as custom compose keys. This is something I discovered some time ago, and only recently revisited due to switching from Debian to Ubuntu. I don’t remember why this works anymore, but anyhow… 1) Install the uim-gtk2.0 package (and uim-qt, if you want). 2) That’s basically it. ツ You can then set your compose keys and whatnot in the System→Preferences→Keyboard menu.
There’s also another way to setup your .XCompose file; you can source the global file, then add your own definitions below that, so you have a more compact compose file (though it becomes subject to upstream’s modifications, which may or may not be something you want). Anyway, mine looks something like this:
# Load the defaults first, so that you can overwrite sequences you don’t like
include "/usr/share/X11/locale/en_US.UTF-8/Compose"
# Custom additions: Typography
<Multi_key> <period> <period> <period> : "…" U2026 # HORIZONTAL ELLIPSIS
<Multi_key> <minus> <less> : "←" leftarrow # LEFTWARDS ARROW
<Multi_key> <bar> <asciicircum> : "↑" uparrow # UPWARDS ARROW
<Multi_key> <minus> <greater> : "→" rightarrow # RIGHTWARDS ARROW
<Multi_key> <bar> <v> : "↓" downarrow # DOWNWARDS ARROW
<Multi_key> <less> <minus> <greater> : "↔" U2194 # LEFT RIGHT ARROW
# etc. etc.
UPDATE:
I just upgraded to Ubuntu 11.04, and the compose keys got broken. Basically, somebody rearranged the keyboard preferences, and you can’t use them to set the compose keys anymore (among other things). The option is probably available graphically, but until I find it, you can revert to the old school way of doing it. Namely,
setxkbmap -option compose:ralt setxkbmap -option ctrl:nocaps The first of these will set the compose key to the Right Alt key, which is what I use. The second command sets the Caps Lock key to function just like another Ctrl key. Put the appropriate lines into your ~/.profile, and you’re up an running again!