I have installed mozc (a Japanese input method editor (IME)) on Ubuntu 14.10. It is working fine. I am able to write in Japanese by going to the icon in the upper-right-hand corner of my screen (what do you call this?) and selecting Hiragana or Katakana from the "Input mode" menu, as in the picture below:
However, this is a very slow process. I imagine there has to be a faster way to switch input modes - a keyboard shortcut or something (like on Windows with Google Japanese Input [to which mozc is related], Alt+` switches between Hiragana and Direct Input). What shortcuts are there for switching input modes, and can they be configured?