           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>.
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