Two Factor Authentication for SSH with Ubuntu

Here is a great very quick Ubuntu two factor authentication setup guide, which I'ved tested to work for Ubuntu 12.04 and 14.04. It sets up two factor authentication for SSH login. You can still login via public key instead, which may be even safer. But it's a good way to prevent bad effects from someone just stealing your password.

Here's a link to the companion authenticator apps for different mobile platforms (Android, iPhone, ...).

Make sure you keep logged in with one session when setting it for remote machines! If you make a mistake you won't be able to log in at all until you correct it.