Defines the number of previous passwords that a user may not reuse. In setting the histsize attribute, it enforces a minimum number of previous passwords a user cannot reuse.
Solution
In /etc/security/user, set the default user stanza histsize attribute to be greater than or equal to 20- chsec -f /etc/security/user -s default -a histsize=20 This means that a user may not reuse any of the previous 20 passwords.