How to Prevent the reuse of old passwords

For RHEL/Fedora distribution 

To remember the last 5 passwords, add the line below to the file /etc/pam.d/system-auth file:

password sufficient /lib/security/pam_unix.so use_authtok md5 shadow remember=5

For Debian/ubuntu distribution

To remember the last 5 passwords, add the line below to the file /etc/pam.d/common-password file:

password sufficient /lib/security/pam_unix.so use_authtok md5 shadow remember=5