Remap key on ubuntu

Remap CAPS_LOCK key to CTRL

$ sudo vi /etc/default/keyboard

then find the line that starts with XKBOPTIONS, and add ctrl:nocaps to make Caps Lock an additional Control key or ctrl:swapcaps to swap Caps Lock and Control.

For example, mine looks like


then run

$ sudo dpkg-reconfigure keyboard-configuration

The reason this way is better is that it will take effect on the virtual consoles (e.g. Ctrl+Alt+F1) as well as in the graphical desktop.