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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 affect 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 complete name (See NAMES for more details).

       -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	complete  name
	       (See  NAMES  for	 more  details).  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 connec-
	       tions) 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.

       The  local family specifies all the local connections at	once. However,
       the server interpreted address "si:localuser:username" can be  used  to
       specify a single	local user. (See the Xsecurity(7) manual page for more
       details.)

       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.	For more information on	the available forms of
       server interpreted addresses, see the Xsecurity(7) manual page.

       The initial access control list for display number n may	be set by  the
       file  /etc/Xn.hosts,  where n is	the display number of the server.  See
       Xserver(1) for details.

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.

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	1.0.7			      XHOST(1)

NAME | SYNOPSIS | DESCRIPTION | OPTIONS | NAMES | DIAGNOSTICS | SEE ALSO | ENVIRONMENT | BUGS | AUTHORS

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