Information
The /etc/security/opasswd file stores the users' old passwords and can be checked to ensure that users are not recycling recent passwords. Forcing users not to reuse their past 5 passwords make it less likely that an attacker will be able to guess the password. Note that these change only apply to accounts configured on the local system.
Solution
Edit the /etc/pam.d/common-password file to include the remember option and conform to site policy as shown:
password sufficient pam_unix.so remember=5