At some point around late 2008 to early 2009, some keycode values (apparently, for the keys that weren't on an XT keyboard) on a standard PC keyboard when running X.org under Linux changed. I don't know whether this was due to a kernel change or an X change. Debian lenny and Ubuntu 8.04 used the old assignment; Debian squeeze and Ubuntu 10.04 used the new assignment.
So I have two xmodmaprc files, one with the old keycodes and one with the new keycodes. How do I determine which one to load from my .xinitrc and .xsession?
I want my startup files to be portable with no hassle, so I want to get rid of my present dependency on the machine name (!). And I don't want to introduce a dependency on Linux distribution versions (and anyway that would be information about the client, but it's information about the server that I need). I already have information about the server at this point in my script (all the symbols listed in xrdb(1) are available as environment variables); hopefully my question reduces to “What parameters to I compare to what values?”.
Note that since I want my startup files to work on machines that I don't administer, keysym reassignments alone are no help. For example, I want to assign my favorite modifier to the Win keys, but I can't predict what keysym will be assigned when I log in. However, if there is an XKB concept I can use in place of keycodes (and is independent of any sysadmin customization, so keysyms won't do), I'm willing to switch to XKB.
xkbcomp -a -dflts -xkb $DISPLAY - | grep 'WIN>'. – geekosaur Mar 15 '11 at 20:35