John the Ripper is a password cracker that can be used to uncover weak passwords on systems on your network. Starting with Ubuntu 9.10 John the Ripper fails to crack passwords because it does not support sha-512 encryption. Below are the steps i used to add sha-512 support to John the Ripper so that you can test the password strength of your newer Ubuntu systems.
1. Download the source for John the Ripper from http://www.openwall.com/john/
2. Extract the tar file with the following command:
tar -xzvf john-1.7.9.tar.gz
3. Open the john-1.7.9/src/Makefile and append "-lcrypt" to line "LDFLAGS = -s"
OLD VALUE: LDFLAGS = -s $(OMPFLAGS)
NEW VALUE: LDFLAGS = -s -lcrypt $(OMPFLAGS)
4. Create a new file called "crypt_fmt.c" and paste the following code into it. Save the file in john-1.7.9/src/