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



NAME
       pam_xauth - PAM module to forward xauth keys between users

SYNOPSIS
       pam_xauth.so [debug] [xauthpath=/path/to/xauth] [systemuser=UID] [targetuser=UID]

DESCRIPTION
       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 users.

       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
       debug
           Print debug information.

       xauthpath=/path/to/xauth
           Specify the path the xauth program (it is expected in /usr/X11R6/bin/xauth,
           /usr/bin/xauth, or /usr/bin/X11/xauth by default).

       systemuser=UID
           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.

       targetuser=UID
           Specify a single target UID which is exempt from the systemuser check.

MODULE TYPES PROVIDED
       Only the session type is provided.

RETURN VALUES
       PAM_BUF_ERR
           Memory buffer error.

       PAM_PERM_DENIED
           Permission denied by import/export file.

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

       PAM_SUCCESS
           Success.

       PAM_USER_UNKNOWN
           User not known.

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

           session  optional  pam_xauth.so



IMPLEMENTATION DETAILS
       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 closed.

FILES
       ~/.xauth/import
           XXX

       ~/.xauth/export
           XXX

SEE ALSO
       pam.conf(5), pam.d(5), pam(7)

AUTHOR
       pam_xauth was written by Nalin Dahyabhai <nalin AT redhat.com>, based on original version by
       Michael K. Johnson <johnsonm AT redhat.com>.



Linux-PAM Manual                            09/19/2013                               PAM_XAUTH(8)