Modules are a very central concept in PAM; after all, they are the
<quote>M
</quote> in
<quote>PAM
</quote>. A PAM module is a self-contained piece of program code that implements the primitives in one or more facilities for one particular mechanism; possible mechanisms for the authentication facility, for instance, include the
<trademark class="registered">UNIX
</trademark> password database, NIS, LDAP and Radius.