xhost - server access control program for X


   xhost [[+-]name ...]


   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.


   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
           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
           controlling host.


   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

   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.,

   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

   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.


   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.


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


   DISPLAY to get the default host and display to use.


   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.


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


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