voluntary, intentional, deliberate, willing mean done or brought about of one's own will. voluntary implies freedom and spontaneity of choice or action without external compulsion. a voluntary confession; intentional stresses an awareness of an end to be achieved. the intentional concealment of vital information deliberate implies full consciousness of the nature of one's act and its consequences. deliberate acts of sabotage
PAM is a framework that assists applications in performing what I'll call authentication-related activities. The core pieces of PAM are a library (libpam) and a collection of PAM modules, which are dynamically linked libraries (.so) files in the folder /lib/security.
Authentication is a process in which the security infrastructure makes sure that the users are who they say they are. In order to do this, the security infrastructure collects the user's credentials, usually in the form of user ID and password, checks those credentials against any credentials' store.