Johnny is GUI version of John.
john, better known as John the Ripper, is a tool to find weak passwords of users in a server. John can use a dictionary or some search pattern as well as a password file to check for passwords. John supports different cracking modes and understands many ciphertext formats, like several DES variants, MD5 and blowfish. It can also be used to extract AFS and Windows NT passwords.
UnShoadow Linux Password details :
The unshadow command will basically combine the data of /etc/passwd and /etc/shadow to create 1 file with username and password details. Usage is quite simple.
cyborg@cyborg:~$ sudo unshadow /etc/passwd /etc/shadow > johntocrack
Crack with Johnny
cyborg@cyborg:~$ sudo johnny
Load UnShadow File you created :
Provide Johnny with word-list .
Password Cracked :