pam_xauth(8)

1PAM_XAUTH(8)                   Linux-PAM Manual                   PAM_XAUTH(8)
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NAME

6       pam_xauth - PAM module to forward xauth keys between users
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SYNOPSIS

9       pam_xauth.so [debug] [xauthpath=/path/to/xauth] [systemuser=UID]
10                    [targetuser=UID]
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DESCRIPTION

13       The pam_xauth PAM module is designed to forward xauth keys (sometimes
14       referred to as "cookies") between users.
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16       Without pam_xauth, when xauth is enabled and a user uses the su(1)
17       command to assume another user's privileges, that user is no longer
18       able to access the original user's X display because the new user does
19       not have the key needed to access the display. pam_xauth solves the
20       problem by forwarding the key from the user running su (the source
21       user) to the user whose identity the source user is assuming (the
22       target user) when the session is created, and destroying the key when
23       the session is torn down.
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25       This means, for example, that when you run su(1) from an xterm session,
26       you will be able to run X programs without explicitly dealing with the
27       xauth(1) xauth command or ~/.Xauthority files.
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29       pam_xauth will only forward keys if xauth can list a key connected to
30       the $DISPLAY environment variable.
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32       Primitive access control is provided by ~/.xauth/export in the invoking
33       user's home directory and ~/.xauth/import in the target user's home
34       directory.
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36       If a user has a ~/.xauth/import file, the user will only receive
37       cookies from users listed in the file. If there is no ~/.xauth/import
38       file, the user will accept cookies from any other user.
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40       If a user has a .xauth/export file, the user will only forward cookies
41       to users listed in the file. If there is no ~/.xauth/export file, and
42       the invoking user is not root, the user will forward cookies to any
43       other user. If there is no ~/.xauth/export file, and the invoking user
44       is root, the user will not forward cookies to other users.
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46       Both the import and export files support wildcards (such as *). Both
47       the import and export files can be empty, signifying that no users are
48       allowed.
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OPTIONS

51       debug
52           Print debug information.
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54       xauthpath=/path/to/xauth
55           Specify the path the xauth program (it is expected in
56           /usr/X11R6/bin/xauth, /usr/bin/xauth, or /usr/bin/X11/xauth by
57           default).
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59       systemuser=UID
60           Specify the highest UID which will be assumed to belong to a
61           "system" user. pam_xauth will refuse to forward credentials to
62           users with UID less than or equal to this number, except for root
63           and the "targetuser", if specified.
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65       targetuser=UID
66           Specify a single target UID which is exempt from the systemuser
67           check.
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MODULE TYPES PROVIDED

70       Only the session type is provided.
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RETURN VALUES

73       PAM_BUF_ERR
74           Memory buffer error.
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76       PAM_PERM_DENIED
77           Permission denied by import/export file.
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79       PAM_SESSION_ERR
80           Cannot determine user name, UID or access users home directory.
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82       PAM_SUCCESS
83           Success.
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85       PAM_USER_UNKNOWN
86           User not known.
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EXAMPLES

89       Add the following line to /etc/pam.d/su to forward xauth keys between
90       users when calling su:
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92           session  optional  pam_xauth.so
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IMPLEMENTATION DETAILS

97       pam_xauth will work only if it is used from a setuid application in
98       which the getuid() call returns the id of the user running the
99       application, and for which PAM can supply the name of the account that
100       the user is attempting to assume. The typical application of this type
101       is su(1). The application must call both pam_open_session() and
102       pam_close_session() with the ruid set to the uid of the calling user
103       and the euid set to root, and must have provided as the PAM_USER item
104       the name of the target user.
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106       pam_xauth calls xauth(1) as the source user to extract the key for
107       $DISPLAY, then calls xauth as the target user to merge the key into the
108       a temporary database and later remove the database.
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110       pam_xauth cannot be told to not remove the keys when the session is
111       closed.
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FILES

114       ~/.xauth/import
115           XXX
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117       ~/.xauth/export
118           XXX
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AUTHOR

124       pam_xauth was written by Nalin Dahyabhai <nalin@redhat.com>, based on
125       original version by Michael K. Johnson <johnsonm@redhat.com>.
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129Linux-PAM Manual                  11/25/2020                      PAM_XAUTH(8)