How to Crack Linux password using John

John the Ripper is a free password cracking software tool. Initially it was developed for the Unix operating system, it now runs on fifteen different platforms, It is one of the most popular password testing and cracking tools as it combines a number of password crackers into one package, autodetects password hash types, and includes a customizable cracker. It can be run against various encrypted password formats including several crypt password hash types most commonly found on various Unix versions.

In This Article you can  learn  hoe to crack Linux user password using tool called John the Ripper and Unshadow.

Install John the Ripper Password Cracking Tool

John the ripper is not installed by default. If you are using Debian / Ubuntu Linux, enter:

rahul@tecgeeks:~$ sudo apt-get install john

Note: RHEL, CentOS, Fedora, Redhat Linux user can grab john the ripper here. Once downloaded use rpm command to Install :

rahul@tecgeeks:~# rpm -ivh john*

How do I use John the ripper to  crack passwords?

First use the unshadow command to combines the /etc/passwd and /etc/shadow files so John can use them to crack. On a normal system you have to run unshadow as root to be able to read the shadow file. So login as root or use sudo command

In Debian / Ubuntu Linux 

rahul@tecgeeks:~$sudo /usr/sbin/unshadow /etc/passwd /etc/shadow > /tmp/crackpasswd.db

In RHEL / CentOS / Fedora

# /usr/bin/unshadow /etc/passwd /etc/shadow > /tmp/crackpasswd.db

WARNING! Do at your own risk

To use John, you just need to supply it a password file created using unshadow command along with desired options.
To Crack Password

rahul@tecgeeks:~$sudo john /tmp/crackpasswd.db

Output:

Created directory: /root/.john
Loaded 5 password hashes with 5 different salts (generic crypt(3) [?/32])
redhat            (rahul)
654321            (test)

This procedure will take some time. To see the cracked passwords, enter:

rahul@tecgeeks:~$john -show /tmp/crackpasswd.db

test:654321:1002:1002:test,,,:/home/test:/bin/bash
rahul:redhat:1003:1003::/home/rahul:/bin/bash
2 passwords cracked, 4 left

Above output clearly indicates - user test has 654321 and rahul has redhat password.

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