XHOST(1) MachTen Programmer’s Manual 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 rudimen-
tary 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 effect access con-
trol 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 cur-
rently 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
dnet DECnet host
nis Secure RPC network name
krb Kerberos V5 principal
local contains only one name, the empty string

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 speci-
fied, or a local user can be specified with just the user-
name 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 fam-
ily. Otherwise the inet family is assumed.

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(3), Xsecurity(3), Xserver(1), xdm(1)

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.
This is not really a bug. If somehow you change a host’s
network address while the server is still running, 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 Release 6 2