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X Display Manager Control Protocol

The X Display Manager Protocol (XDMCP) is used by a display manager (usually the xdm program or the dtlogin program under CDE) for managing remote X Window servers, mostly X terminals. The communication between display manager and X Window server comprises the following simplified steps:

During its initialization the X Window server tries to connect to a display manager on the network which is willing to manage the server.

If the display manager is willing to manage the server, it begins the login dialog.

After the user successfully logged in, the display manager starts a session.

When the user terminates the session, the login dialog is displayed again.

XDMCP has to be configured only if the display manager and the xmetax program are running on different machines. The statements:

xdmcpMode [broadcast|indirect|query|off] [once]
xdmcpHost name_of_the_XDMCP_host
xdmcpPort XDMCP_port_number

configure the XDMCP support:

broadcast: the xmetax program sends XDMCP queries to all hosts on the network.

indirect: the xmetax program sends indirect XDMCP queries to the host specified by the xdmcpHost statement, which passes them on to certain other hosts.

query: the xmetax program sends XDMCP queries to the host specified by the xdmcpHost statement only.

off disables the XDMCP support. This is the default value.

once lets the xmetax program terminate after the execution of one session only. The xdmcpPort statement specifies the port for the XDMCP communication. The default value is the standard port number 177.

The statements

xdmcpDisplayClass display_class
xdmcpDisplayID display_ID

identify the xmetax program to the display manager. The default values are  X-SOFTWARE-XMETAX and X-SOFTWARE-XMETAX-system_ID-display_number, respectively.

The statement

xdmcpAuthorizationCookie key

specifies a key for the authorization by the XDM-AUTHORIZATION-1 method (Authorization).

If XCMCP is configured by arguments in a serverCommand statement (X Window server), these are also used by the XmetaX proxy.

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