XHOST(1X11)             COMMAND REFERENCE             XHOST(1X11)



NAME
     xhost - server access control program for X

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

     This is a supported client.

DESCRIPTION
     The xhost program is used to add and delete hosts to the
     list of machines that are allowed to make connections to the
     X server.  This provides a rudimentary form of privacy
     control and security.  It is only sufficient for a
     workstation (single user) environment, although it does
     limit the worst abuses. Environments which 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 program is usually run either from a
     startup file or it is run interactively to give access to
     other users.

     Hostnames that are followed by two colons (::) are used in
     checking DECnet connections; all other hostnames are used
     for TCP/IP connections.

OPTIONS
     The control program xhost accepts the following command line
     options described here.  For security, the options that
     effect access control may only be run from the same machine
     as the server.

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

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



Printed 3/22/89                                                 1

XHOST(1X11)             COMMAND REFERENCE             XHOST(1X11)



     +                   Access is granted to everyone, even if
                         they aren't on the list of allowed hosts
                         (i.e., access control is turned off).

     -                   Access is restricted to only those
                         machines on the list of allowed hosts
                         (i.e., access control is turned on).

     nothing             If no command line arguments 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 running.

ENVIRONMENT
     DISPLAY        To get the default host and display to use.

FILES
     /etc/X*.hosts

CAVEATS
     You can't specify a display on the command line because
     -display is a valid command line argument (indicating that
     you want to remove the machine named ``display'' from the
     access list).

SEE ALSO
     X(1x11), Xserver(1x11).

AUTHORS
     Bob Scheifler, MIT Laboratory for Computer Science, Jim
     Gettys, MIT Project Athena (DEC).




















Printed 3/22/89                                                 2

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