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
~/.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
~/.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
file, and the invoking user is root,
the user will not forward cookies to
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.
Print debug information.
Specify the path the xauth program (it is expected in
/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.
Memory buffer error.
Permission denied by import/export file.
Cannot determine user name, UID or access users home directory.
User not known.
Add the following line to
forward xauth keys between users when calling su:
session optional pam_xauth.so