PAM_XAUTH(8)                  Linux-PAM Manual                  PAM_XAUTH(8)

NAME         top

       pam_xauth - PAM module to forward xauth keys between users

SYNOPSIS         top [debug] [xauthpath=/path/to/xauth] [systemuser=UID]

DESCRIPTION         top

       The pam_xauth PAM module is designed to forward xauth keys (sometimes
       referred to as "cookies") between users.

       Without pam_xauth, when xauth is enabled and a user uses the su(1)
       command to assume another user's privileges, that user is no longer
       able to access the original user's X display because the new user
       does not have the key needed to access the display. pam_xauth solves
       the problem by forwarding the key from the user running su (the
       source user) to the user whose identity the source user is assuming
       (the target user) when the session is created, and destroying the key
       when the session is torn down.

       This means, for example, that when you run su(1) from an xterm
       session, you will be able to run X programs without explicitly
       dealing with the xauth(1) xauth command or ~/.Xauthority files.

       pam_xauth will only forward keys if xauth can list a key connected to
       the $DISPLAY environment variable.

       Primitive access control is provided by ~/.xauth/export in the
       invoking user's home directory and ~/.xauth/import in the target
       user's home directory.

       If a user has a ~/.xauth/import file, the user will only receive
       cookies from users listed in the file. If there is no ~/.xauth/import
       file, the user will accept cookies from any other user.

       If a user has a .xauth/export file, the user will only forward
       cookies to users listed in the file. If there is no ~/.xauth/export
       file, and the invoking user is not root, the user will forward
       cookies to any other user. If there is no ~/.xauth/export file, and
       the invoking user is root, the user will not forward cookies to other

       Both the import and export files support wildcards (such as *). Both
       the import and export files can be empty, signifying that no users
       are allowed.

OPTIONS         top

           Print debug information.

           Specify the path the xauth program (it is expected in
           /usr/X11R6/bin/xauth, /usr/bin/xauth, or /usr/bin/X11/xauth by

           Specify the highest UID which will be assumed to belong to a
           "system" user. pam_xauth will refuse to forward credentials to
           users with UID less than or equal to this number, except for root
           and the "targetuser", if specified.

           Specify a single target UID which is exempt from the systemuser


       Only the session type is provided.

RETURN VALUES         top

           Memory buffer error.

           Permission denied by import/export file.

           Cannot determine user name, UID or access users home directory.


           User not known.

EXAMPLES         top

       Add the following line to /etc/pam.d/su to forward xauth keys between
       users when calling su:

           session  optional


       pam_xauth will work only if it is used from a setuid application in
       which the getuid() call returns the id of the user running the
       application, and for which PAM can supply the name of the account
       that the user is attempting to assume. The typical application of
       this type is su(1). The application must call both pam_open_session()
       and pam_close_session() with the ruid set to the uid of the calling
       user and the euid set to root, and must have provided as the PAM_USER
       item the name of the target user.

       pam_xauth calls xauth(1) as the source user to extract the key for
       $DISPLAY, then calls xauth as the target user to merge the key into
       the a temporary database and later remove the database.

       pam_xauth cannot be told to not remove the keys when the session is

FILES         top



SEE ALSO         top

       pam.conf(5), pam.d(5), pam(8)

AUTHOR         top

       pam_xauth was written by Nalin Dahyabhai <>, based on
       original version by Michael K. Johnson <>.

COLOPHON         top

       This page is part of the linux-pam (Pluggable Authentication Modules
       for Linux) project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug report for
       this manual page, see ⟨⟩.
       This page was obtained from the tarball Linux-PAM-1.3.0.tar.gz
       fetched from ⟨⟩ on 2017-03-13.  If
       you discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for the
       page, or you have corrections or improvements to the information in
       this COLOPHON (which is not part of the original manual page), send a
       mail to

Linux-PAM Manual                 04/01/2016                     PAM_XAUTH(8)