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+pam_listfile — deny or allow services based on an arbitrary file
+
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+
+DESCRIPTION
+
+pam_listfile is a PAM module which provides a way to deny or allow services
+based on an arbitrary file.
+
+The module gets the item of the type specified -- user specifies the username, 
+PAM_USER; tty specifies the name of the terminal over which the request has
+been made, PAM_TTY; rhost specifies the name of the remote host (if any) from
+which the request was made, PAM_RHOST; and ruser specifies the name of the
+remote user (if available) who made the request, PAM_RUSER -- and looks for an
+instance of that item in the file=filename. filename contains one line per item
+listed. If the item is found, then if sense=allow, PAM_SUCCESS is returned,
+causing the authorization request to succeed; else if sense=deny, PAM_AUTH_ERR
+is returned, causing the authorization request to fail.
+
+If an error is encountered (for instance, if filename does not exist, or a
+poorly-constructed argument is encountered), then if onerr=succeed, PAM_SUCCESS
+is returned, otherwise if onerr=fail, PAM_AUTH_ERR or PAM_SERVICE_ERR (as
+appropriate) will be returned.
+
+An additional argument, apply=, can be used to restrict the application of the
+above to a specific user (apply=username) or a given group (apply=@groupname).
+This added restriction is only meaningful when used with the tty, rhost and 
+shell items.
+
+Besides this last one, all arguments should be specified; do not count on any
+default behavior.
+
+No credentials are awarded by this module.
+
+OPTIONS
+
+item=[tty|user|rhost|ruser|group|shell]
+
+    What is listed in the file and should be checked for.
+
+sense=[allow|deny]
+
+    Action to take if found in file, if the item is NOT found in the file, then
+    the opposite action is requested.
+
+file=/path/filename
+
+    File containing one item per line. The file needs to be a plain file and
+    not world writable.
+
+onerr=[succeed|fail]
+
+    What to do if something weird happens like being unable to open the file.
+
+apply=[user|@group]
+
+    Restrict the user class for which the restriction apply. Note that with
+    item=[user|ruser|group] this does not make sense, but for item=[tty|rhost|
+    shell] it have a meaning.
+
+quiet
+
+    Do not treat service refusals or missing list files as errors that need to
+    be logged.
+
+EXAMPLES
+
+Classic 'ftpusers' authentication can be implemented with this entry in /etc/
+pam.d/ftpd:
+
+#
+# deny ftp-access to users listed in the /etc/ftpusers file
+#
+auth    required       pam_listfile.so \
+        onerr=succeed item=user sense=deny file=/etc/ftpusers
+
+
+Note, users listed in /etc/ftpusers file are (counterintuitively) not allowed
+access to the ftp service.
+
+To allow login access only for certain users, you can use a /etc/pam.d/login
+entry like this:
+
+#
+# permit login to users listed in /etc/loginusers
+#
+auth    required       pam_listfile.so \
+        onerr=fail item=user sense=allow file=/etc/loginusers
+
+
+For this example to work, all users who are allowed to use the login service
+should be listed in the file /etc/loginusers. Unless you are explicitly trying
+to lock out root, make sure that when you do this, you leave a way for root to
+log in, either by listing root in /etc/loginusers, or by listing a user who is
+able to su to the root account.
+
+AUTHOR
+
+pam_listfile was written by Michael K. Johnson <johnsonm@redhat.com> and Elliot
+Lee <sopwith@cuc.edu>.
+