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xhost - server access control program for X
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
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.
A complete name has the syntax ``family:name''
where the families are as follows:
- Prints a usage
- 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
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 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 the inet family is assumed.
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 use.
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.
Bob Scheifler, MIT Laboratory
for Computer Science,
Jim Gettys, MIT Project Athena (DEC).
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