I have Ubuntu 12.04 LTS and I want to disable the Ctrl+Alt+Del shortcut because it interferes with the same shortcut in my VirtualBox's Windows. How can I do this?
I tried to remove it from keyboard shortcuts in settings but it didn't help.
You cannot send Ctrl+Alt+Del to VirtualBox by pressing those exact keys on the keyboard, even if they are not reassigned in Unity. You can send the Ctrl+Alt+Del combination in VirtualBox at least two ways:
The host key is usually the Right Ctrl key, but you can change that to be something else. If you have not changed it, try pressing Ctrl-Del in your VirtualBox to send Ctrl+Alt+Del. Make sure you use the Right Ctrl key and not the Left one.