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XHOST(1)							      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 secu-
       rity.  It is only sufficient for a workstation (single  user)  environ-
       ment,  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 authenti-
       cation 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.

       [+]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
	       only  option that may be used from machines other than the con-
	       trolling host.

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

       inet	 Internet host (IPv4)
       inet6	 Internet host (IPv6)
       dnet	 DECnet host
       nis	 Secure RPC network name
       krb	 Kerberos V5 principal
       local	 contains only one name, the empty string
       si	 Server Interpreted

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

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

       For backward compatibility with pre-R6 xhost, names that contain an at-
       sign (@) are assumed to be in  the  nis	family.	  Otherwise  they  are
       assumed to be Internet addresses. If compiled to support IPv6, then all
       IPv4 and IPv6 addresses returned by getaddrinfo(3)  are	added  to  the
       access list in the appropriate inet or inet6 family.

       Server interpreted addresses consist of a case-sensitive type tag and a
       string representing a given value, separated by a colon.	 For  example,
       "si:hostname:almas"  is	a server interpreted address of type hostname,
       with a value of almas.

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

FILES
       /etc/X*.hosts

SEE ALSO
       X(7), Xsecurity(7), Xserver(1), xdm(1), xauth(1), getaddrinfo(3)

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, unless you use
       the server-interpreted hostname type address.  If somehow you change  a
       host's  network	address while the server is still running, and you are
       using a network-address based form of  authentication,  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).



X Version 11			  xhost 1.0.1			      XHOST(1)
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