Passwords
For increased security, cracklib will not accept passwords that are based on a dictionary word or differ from the previous password by less than three characters. This behaviour is configured in /etc/pam.d/common-password.
Adding to the forbidden password list
It is sometimes appropriate to add passwords from the forbidden passwords list. For example, the password may not be in the system-wide 'words' file, or UWCS-specific terms could be used as passwords.
To modify the list:
Edit /usr/share/dict/cracklib
Run update-cracklib as root.