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.

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).