Since authentication mechanisms constantly evolve, it is important to shield the system-entry services and users from such changes.With the Pluggable Authentication Module (PAM) framework, we can provide pluggability for a variety of systementry services -not just system authentication per se, but also for account, session and password management.PAM's ability to stack authentication modules can be used to integrate login with different authentication mechanisms such as RSA, DCE, and Kerberos, and thus unify login mechanisms.The PAM framework can also provide easy integration of smart cards into the system.