Yvo Van Doorn is a self-proclaimed "interoperability geek," Currently employed at Likewise, Yvo has a background managing large Linux, UNIX, Mac and Windows infrastructures at large technology companies. Ask him how many unique VM OSs he has running on his personal machine. The number might shock you.
Every time you log into a Linux system, you're using the Pluggable Authentication Modules (PAM). Let's take a closer look what's going on under the hood.