Unless you've swapped CapsLock for Esc. Then it's easy as pie. In ~/.Xmodmap: ! Swap Caps Lock with Esc remove Lock = Caps_Lock keysym Escape = C

Unless you've swapped CapsLock for Esc. Then it's easy as pie. In ~/.Xmodmap: ! Swap Caps Lock with Esc remove Lock = Caps_Lock keysym Escape = Caps_Lock keysym Caps_Lock = Escape add Lock = Caps_Lock