NAME

     pam_alreadyloggedin — Already-logged-in PAM module

SYNOPSIS

     [service-name] module-type control-flag pam_alreadyloggedin [options]

DESCRIPTION

     The Already-logged-in authentication service module for PAM, pam_alreadyloggedin provides functionality for
     only one PAM category: authentication.  In terms of the module-type parameter, this is the “auth” feature.
     It also provides null functions for other PAM categories.

   Already-logged-in Authentication Module
     The Already-logged-in authentication component (pam_sm_authenticate()), returns success if and only if the
     target user's ID is identical to a current login specified in the utmp(5) database and verified with
     matching permissions on that login's respective terminal in /dev.  If a user shows up in w(8) output, they
     will generally be allowed to authenticate using this method.

     The following options may be passed to the authentication module:

     debug                           Enable verbose output to syslog at LOG_DEBUG level.

     no_debug                        Disable verbose output to syslog even it's enabled at compile time.

     no_root                         Never allow login with a target user ID of zero.

     restrict_tty=ttyglob*           Only allow login if the terminal device currently being authenticated on
                                     matches ttyglob*.  The ttyglob* argument is specified as a shell glob, and
                                     checked using the fnmatch(3) function. For example,
                                     restrict_tty=/dev/tty[1-6] allows logging from text consoles of physical
                                     terminal only.

     restrict_loggedin_tty=ttyglob*  Disallow recognition that the user is already logged in unless the terminal
                                     device logged in upon matches ttyglob*.

EXAMPLE

     Modify auth section of the /etc/pam.d/login file like following:

           auth required   /lib/security/pam_securetty.so
           auth sufficient /lib/security/pam_alreadyloggedin.so no_root
           auth required   /lib/security/pam_stack.so service=system-auth

BUGS

     FreeBSD version expects /dev/ prefix in restrict_tty value, but value of restrict_loggedin_tty should be
     without them.  Linux version expects /dev/ in both cases.

SEE ALSO

     fnmatch(3), getuid(2), stat(2), utmp(5), w(8), pam.conf(5), pam(8)

AUTHORS

     Adopted for Linux PAM by Ilya Evseev at Jan 2004.

     The original pam_alreadyloggedin module and this manual page were developed for the FreeBSD Project by NAI
     Labs and ThinkSec AS, the Security Research Division of Network Associates, Inc.  under DARPA/SPAWAR
     contract N66001-01-C-8035 (“CBOSS”), as part of the DARPA CHATS research program.