pam_xauth -- PAM module to forward xauth keys between users
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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.

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.

AUTHOR

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