Entry from /usr/share/X11/xorg.conf.d/10-evdev.conf:
Section "InputClass"
Identifier "evdev keyboard catchall"
MatchIsKeyboard "on"
MatchDevicePath "/dev/input/event*"
Driver "evdev"
Option "XkbModel" "pc105"
Option "XkbLayout" "us_intl"
Option "XkbOptions" "compose:menu"
EndSection
The compose key is used to type "ß" because for a long while I couldn't for the life of me figure out how to get "Alt-Gr" to work on Gentoo. And then I found out that all I had to do was to map "Mode_switch" to the right Alt keycode.
Using xev, I found that the keycode for the right Alt is 108. So this is my entry in ~/.Xmodmap
keycode 108 = Mode_switch
And just for fun, this is how to map the "s" key so that you can type the capital eszett ẞ (not ß)
keycode 39 = s S ssharp U1E9E
For those who are curious as to how the keycode format works: here's the explanation I've taken from this website:
keycode = <1> <2> <3> <4>4>3>2>1> <5> <6> <7> <8>8>7>6>5>
<1>
<2>
<3> <"Mode_switch"-key>
<4> 4>3> 2> 1>
<5> <"Num_Lock"-key>
<6> -
<7> <"Num_Lock"-"Mode_switch"-key>
<8> 8>7>6>5>