Looking for two factor authentication for SSH logins to your Linux systems? Well then today is your lucky day - nixCraft has you covered.
nixCraft has a really nice write-up for how to secure your Linux desktop and SSH login utilizing Google Authenticator's two factor authentication. Click through the link below for complete details of the requirements & related setup procedure; including screen shots of how it's all accomplished.
How To Protect Linux SSH Login With Google Authenticator