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
Both the import and export files support wildcards (such as *). Both
the import and export files can be empty, signifying that no users
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
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
Memory buffer error.
Permission denied by import/export file.
Cannot determine user name, UID or access users home directory.
User not known.
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
This page is part of the linux-pam (Pluggable Authentication Modules
for Linux) project. Information about the project can be found at
⟨https://fedorahosted.org/linux-pam/⟩. If you have a bug report for
this manual page, see ⟨https://fedorahosted.org/linux-pam/report⟩.
This page was obtained from the tarball Linux-PAM-1.3.0.tar.gz
fetched from ⟨http://www.linux-pam.org/library/⟩ on 2017-03-13. If
you discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for the
page, or you have corrections or improvements to the information in
this COLOPHON (which is not part of the original manual page), send a
mail to firstname.lastname@example.org
Linux-PAM Manual 04/01/2016 PAM_XAUTH(8)