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xhost - server access control program
xhost [[+-]name ...]
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.
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.
A complete name has
the syntax “family:name” where the families are as follows:
- Prints a usage message.
- 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.
- 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).
- 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.
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.
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)
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.
- to get the default host and display to
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.
Bob Scheifler, MIT Laboratory for Computer Science,
Jim Gettys, MIT Project Athena (DEC).
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