Available PAM Modules

pam_deny - always denies access.
pam_warn - simply writes a message to the log file (using syslog).
pam_unix_auth, pam_unix_acct, pam_unix_passwd, pam_unix_session - supply the "historic" behavior of a unix system's authentication.
pam_securetty - verifies that the user's tty is listed in /etc/securetty.
pam_cracklib - checks passwords against a dictionary, and verifies they are not too easy to crack.
pam_env - allows (un)setting environment variables.
pam_ftp - used to allow 'anonymous' access to ftp servers.
pam_krb4 - supports kerberos-based authentication.
pam_lastlog - adds log entries to /var/adm/wtmp.
pam_limits - defines resource-limits for the session (man limit).
pam_nologin - denies access when the file "/etc/nologin" exists.
pam_rhosts_auth - standard ".rhosts" authentication.