xhost(1X)                                               xhost(1X)



NAME
     xhost - controls access to the server

SYNOPSIS
     xhost [[+]hostname] ...
     xhost [[-]hostname] ...

DESCRIPTION
     xhost adds hosts to and deletes hosts from the list of
     machines that are allowed to make connections to the X
     server, as specified by hostname.  The list is used to pro-
     vide a rudimentary form of privacy control and security.  It
     is only sufficient for a workstation (single-user) environ-
     ment, although it does limit the worst abuses.  Environments
     that require more sophisticated measures should use the
     hooks in the protocol for passing authentication data to the
     server.

     The server initially allows network connections only from
     programs running on the same machine or from machines listed
     in the file /etc/X*.hosts, where * is the display number of
     the server.  The xhost command is usually either run from a
     startup file or run interactively to give access to other
     users.

   Options
     The xhost command accepts the command-line options described
     below.  For security, the options that effect access control
     may only be run from the same machine as the server.

     [+]hostname
             Adds the given host name to the list of machines
             that are allowed to connect to the X server. The
             plus sign (+) is optional.

     -hostname
             Removes the given host name from the list of
             machines that are allowed to connect to the server.
             Existing connections are not broken, but new connec-
             tion attempts are denied.  Note that the current
             machine is allowed to be removed; however, further
             connections, including attempts to add it back, are
             not permitted.  Resetting the server and thereby
             breaking all connections, is the only way to allow
             local connections again.

     +       Access is granted to everyone, even if they aren't
             on the list of allowed hosts (that is, access con-
             trol is turned off).

     -       Access is restricted to only those machines on the
             list of allowed hosts (that is, access control is



November, 1990                                                  1

xhost(1X)                                               xhost(1X)



             turned on).

     If no command-line options are given, the list of hosts that
     are allowed to connect is printed on the standard output
     along with a message indicating whether access control is
     currently enabled.  This is the only option that may be used
     from machines other than the one on which the server is run-
     ning.

   Environment variables
     The xhost command uses the following environment variable:

     DISPLAY Specifies the default host, display number, and
             screen.

LIMITATIONS
     You can't specify a display on the command line because
     -display is a valid command-line option, indicating that you
     want to remove the machine named display from the access
     list.

NOTES
     Copyright 1988, Massachusetts Institute of Technology.
     See X(1) for a full statement of rights and permissions.

     Authors: Bob Scheifler, MIT Laboratory for Computer Science,
     and Jim Gettys, MIT Project Athena (DEC)

FILES
     /etc/X*.hosts
             Specifies hosts that are allowed network connec-
             tions.

SEE ALSO
     X(1X), XmacII(1X)




















2                                                  November, 1990