xhost(1)

     NAME
          xhost - server access control program for X

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

     DESCRIPTION
          The xhost program is used to add and delete host names to
          the list 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 implement the user-based mechanism or use the hooks
          in the protocol for passing other authentication data to the
          server.

     OPTIONS
          xhost accepts the following command line options described
          below.  For security, the options that effect access control
          may only be run from the "controlling host".  For
          workstations, this is the same machine as the server.  For X
          terminals, it is the login host.

          -help   Prints a usage message.

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

          -hostname
                  The given hostname is removed from the list of
                  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.

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

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

          nothing If no command line arguments are given, a message
                  indicating whether or not access control is
                  currently enabled is printed, followed by the list
                  of those allowed to connect.  This is the only
                  option that may be used from machines other than the
                  controlling host.

     NAMES
          A complete name has the syntax ``family:name'' where the
          families are as follows:

          inet      Internet host
          dnet      DECnet host
          nis       Secure RPC network name
          krb       Kerberos V5 principal
          local     contains only one name, the empty string

          The family is case insensitive.  The format of the name
          varies with the family.

          For backward compatibility with pre-R6 xhost, names that
          contain an at-sign (@) are assumed to be in the nis family.
          Otherwise the inet family is assumed.

     DIAGNOSTICS
          For each hostname added to the access control list, a line
          of the form "hostname being added to access control list" is
          printed.  For each hostname removed from the access control
          list, a line of the form "hostname being removed from access
          control list" is printed.

     FILES
          /etc/X*.hosts

     SEE ALSO
          X(1), Xsecurity(1), Xserver(1), xdm(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).

          The X server stores network addresses, not host names.  This
          is not really a bug.  If somehow you change a host's network
          address while the server is still running, xhost must be
          used to add the new address and/or remove the old address.

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