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(8)

AUTHOR

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

Linux-PAM Manual						    04/01/2010							      PAM_XAUTH(8)