pam_xauth(8) System Administrator's Manual pam_xauth(8)
pam_xauth - forward xauth keys between users
session optional /lib/security/pam_xauth.so arguments
pam_xauth.so is designed to forward xauth keys (sometimes referred to as "cookies")
Without pam_xauth, when xauth is enabled and a user uses the su command to assume another
user's priviledges, 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 from an xterm sesssion, you will be able to
run X programs without explicitly dealing with the xauth command or ~/.Xauthority files.
pam_xauth will only forward keys if xauth can list a key connected to the $DISPLAY envi-
Primitive access control is provided by ~/.xauth/export in the invoking user's home direc-
tory 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
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.
debug Turns on debugging messages sent to syslog.
Specify the path the xauth program (the default is /usr/X11R6/bin/xauth).
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. The application must call both pam_open_session() and pam_close_ses-
sion() 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 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
pam_xauth cannot be told not to remove the keys when the session is closed.
Let's hope not, but if you find any, please report them via the "Bug Track" link at
Nalin Dahyabhai <firstname.lastname@example.org>, based on original version by Michael K. Johnson <john-
Red Hat Linux 2001/9/27 pam_xauth(8)