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.

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 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.

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).