full source: http://www.linuxjournal.com/content/hack-and-password-cracking-gpus-part-i-setup
passwords are encrypted into a hash and are stored in /etc/shadow
To look in the shadow file, type in a terminal sudo cat /etc/shadow
look at 'man shadow' for the full definition.
The hashes are delimited by the $ sign in this format
$id $salt $encrypted
Where $id 1 = MD5 5 = SHA-256 6 = SHA-512
Also look here for more info http://www.cyberciti.biz/faq/understanding-etcshadow-file/