XHOST(1)                    X Version 11(Release 5)                    XHOST(1)


NAME
      xhost - server access control program for X

SYNOPSIS
      xhost [[+-]name ...]

DESCRIPTION
      The xhost program is used to add and delete host names or user names to
      the list allowed to make connections to the X server.  In the case of
      hosts, 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.

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

      User names contain an at-sign (@).  When Secure RPC is being used, the
      network independent netname (e.g., "unix.uid@domainname") can be
      specified, or a local user can be specified with just the username and a
      trailing at-sign (e.g., "joe@").

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.

      [+]name The given name (the plus sign is optional) is added to the list
              allowed to connect to the X server.  The name can be a host name
              or a user name.

      -name   The given name is removed from the list of allowed to connect to
              the server.  The name can be a host name or a user name.
              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 everyone, 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


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XHOST(1)                    X Version 11(Release 5)                    XHOST(1)


              only option that may be used from machines other than the
              controlling host.

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

FILES
      /etc/X*.hosts

SEE ALSO
      X(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).

      This is not really a bug, but the X server stores network addresses, not
      host names.  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.

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).



















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