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)

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