pam_xauth(8) — Linux manual page


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

       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         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 default).

           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 check.


       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


           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 closed.

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