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 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.

Hostnames that are followed by two colons (::) are used in checking DECnet connections; all other hostnames are used for TCP/IP connections.

User names contain an at-sign (@). When Secure RPC is being used, the network independent netname (e.g., "unix.uid@domainname") can be specified, or a local user can be specified with just the username and a trailing at-sign (e.g., "joe@").

OPTIONS
Xhost accepts the following command line options described below. For security, the options that effect 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.

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 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.

DIAGNOSTICS
For each name added to the access control list, a line of the form "name being added to access contro list" is printed. For each name removed from the access control list, a line of the form "name being removed from access contro list" is printed.

FILES
/etc/X*.hosts

SEE ALSO
X(1), 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).

This is not really a bug, but the X server stores network addresses, not host names. 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.

COPYRIGHT
Copyright 1988, Massachusetts Institute of Technology.
See X(1) for a full statement of rights and permissions.

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