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
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.
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
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
Memory buffer error.
Permission denied by import/export file.
Cannot determine user name, UID or access users home
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
This page is part of the linux-pam (Pluggable Authentication
Modules for Linux) project. Information about the project can be
found at ⟨http://www.linux-pam.org/⟩. If you have a bug report
for this manual page, see ⟨//www.linux-pam.org/⟩. This page was
obtained from the tarball Linux-PAM-1.3.0.tar.bz2 fetched from
⟨http://www.linux-pam.org/library/⟩ on 2021-08-27. 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 email@example.com
Linux-PAM Manual 04/01/2016 PAM_XAUTH(8)