System Settings/Input Devices

Information

This article refers to KDE SC 4.5.1 version or later.

Keyboard

Enable Control + Alt + Backspace to kill X-Server

Under Advanced tab, make sure Configure keyboard options is enabled. Then look in the list below for "Key sequence to kill the X server". Under it, you should be able to check Control + Alt + Backspace. Once done, click on Apply.

Enable Compose key

Compose is a feature that allows you to write any character you want, no matter the keyboard layout you are using, by pressing a certain key (Compose key) and a series of keys. You could, i.e., associate ‘~’ and ‘n’ characters so they get replaced by a ‘ñ’ character when they are pressed after pressing Compose key. There are many default key combinations, and you can customize Compose configuration file so it better fits your specific needs. You will find more information here.

To enable this feature, first make sure Configure keyboard options is enabled under Advanced tab. Then, check a key from Compose key position tree. Finally, click Apply. From now on, you will be able to use that key as Compose key.