XHOST(1)                 USER COMMANDS                   XHOST(1)



NAME
     xhost - server access control program for X

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

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  con-
     trol  and security.  It is only sufficient for a workstation
     (single user) environment, although it does limit the  worst
     abuses.  Environments which require more sophisticated meas-
     ures 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 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
     Xhost accepts the following 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
             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 connec-
             tion 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.

     +       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



X Version 11         Last change: Release 4                     1

XHOST(1)                 USER COMMANDS                   XHOST(1)



             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  or not 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.

FILES
     /etc/X*.hosts

SEE ALSO
     X(1), Xserver(1)

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

BUGS
     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).

COPYRIGHT
     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,
     Jim Gettys, MIT Project Athena (DEC).






















X Version 11         Last change: Release 4                     2