Ubuntu: Make Ctrl-Space work in RubyMine, Emacs, or other tools

I was annoyed that RubyMine's autocompletion did not work via Ctrl+Space for me. In fact, it did not work in any application.

Turns out that keyboard combination was hijacked by Ubuntu as it's the default for switching input languages (i.e. keyboard layouts). If you use only 1 language/layout, you will not notice except for the key not working.

To fix it, do the following:

1. Run ibus-setup (e.g. from a terminal). This will open a GUI dialog.
2. In the 1st tab you should see "Next Input Method" followed by "<Control>space".
3. Click the "..." button on the right of it, and change it. I changed mine to "<Control><Shift><Super>space".
4. Click the "Apply" button, and then the "OK" button.
5. You may now close the iBus settings application.

Ctrl+Space should now work for you.