DOKK / manpages / debian 10 / libpam-alreadyloggedin / pam_alreadyloggedin.8.en
PAM_ALREADYLOGGEDIN(8) System Manager's Manual PAM_ALREADYLOGGEDIN(8)

pam_alreadyloggedin — Already-logged-in PAM module

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

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.

The Already-logged-in authentication component (()), 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:

Enable verbose output to syslog at LOG_DEBUG level.
Disable verbose output to syslog even it's enabled at compile time.
Never allow login with a target user ID of zero.
=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.
=ttyglob*
Disallow recognition that the user is already logged in unless the terminal device logged in upon matches ttyglob*.

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

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.

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

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.

January 30, 2004 Linux-PAM