UBTU-16-010230 - Passwords must be prohibited from reuse for a minimum of five generations.
Password complexity, or strength, is a measure of the effectiveness of a password in resisting attempts at guessing and brute-force attacks. If the information system or application allows the user to consecutively reuse their password when that password has exceeded its defined lifetime, the end result is a password that is not changed as per policy requirements.
Configure the Ubuntu operating system prevents passwords from being reused for a minimum of five generations. Add or modify the 'remember' parameter value to the following line in '/etc/pam.d/common-password' file: password [success=1 default=ignore] pam_unix.so obscure sha512 remember=5 rounds=5000