pam_pwhistory.so  [
        debug
      ] [
        use_authtok
      ] [
        enforce_for_root
      ] [
        remember=N
      ] [
        retry=N
      ] [
        authtok_type=STRING
      ]
This module saves the last passwords for each user in order to force password change history and keep the user from alternating between the same password too frequently.
This module does not work together with kerberos. In general, it does not make much sense to use this module in conjunction with NIS or LDAP, since the old passwords are stored on the local machine and are not available on another machine for password history checking.
debug
        Turns on debugging via syslog(3).
use_authtok
        
           When password changing enforce the module to use the new password
           provided by a previously stacked password
           module (this is used in the example of the stacking of the
           pam_cracklib module documented below).
          
enforce_for_root
        If this option is set, the check is enforced for root, too.
remember=N
        
            The last N passwords for each
            user are saved in /etc/security/opasswd.
            The default is 10.
          
retry=N
          
              Prompt user at most N times
              before returning with error. The default is
              1.
            
authtok_type=STRING
          See pam_get_authtok(3) for more details.
No new password was entered, the user aborted password change or new password couldn't be set.
Password history was disabled.
Password was rejected too often.
User is not known to system.
An example password section would be:
#%PAM-1.0
password     required       pam_pwhistory.so
password     required       pam_unix.so        use_authtok
      
In combination with pam_cracklib:
#%PAM-1.0
password     required       pam_cracklib.so    retry=3
password     required       pam_pwhistory.so   use_authtok
password     required       pam_unix.so        use_authtok