How to swap Ctrl-CapsLock on X

method 1.

$ /usr/bin/setxkbmap -option "ctrl:swapcaps"

method 2.
/etc/X11/xorg.conf

Section "InputDevice"
  Identifier "Keyboard0"
  ...
  Option "XkbOptions" "ctrl:swapcaps"
EndSection

References
http://serverfault.com/questions/10437/how-do-you-swap-the-caps-lock-to-control-in-xfce
http://lrobot.sinaapp.com/?p=314
http://wiki.linuxquestions.org/wiki/Swap_Caps_Lock_and_Ctrl