NAME

xhost − server access control program for X. 

SYNTAX

xhost [options]

DESCRIPTION

The xhost program is used to add and delete hostnames (or user names) to and from 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 that require more sophisticated measures should implement the user-based mechanism, or use the hooks in the protocol for passing authentication data to the server.  (See Appendix A, Managing Your Environment, for an introduction to server access control. 

The server initially allows network connections only from programs running on the same machine or from machines listed in the file /etc/Xn.hosts (where n is the display number of the server).  The xhost program is usually run either from a startup file or interactively to give access to other users. 

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@"). 

If no command-line options are given, a message indicating whether or not access control is currently enabled is printed on the standard output followed by the list of those allowed to connect.  This is the only option that can be used from machines other than the controlling host. 

OPTIONS

xhost accepts the 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 hostname or a user name. 

-nameThe given name is removed from the list allowed to connect to the server.  The name can be a hostname 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). 

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/Xn.hosts

BUGS

You can’t specify a display on the command line because -display indicates 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 hostnames.  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. 

SEE ALSO

X, Xserver, xauth, xdm; the section "Using -display" in Chapter 3, Working in the X Environment; Appendix A, Managing Your Environment. 

AUTHORS

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