By default, ncdinstall checks for the presence of XDM software on the boot host. If XDM is not running, ncdinstall can install or enable it.

XDM runs on login hosts and terminals and manages the user's X session from login to logout. XDM can be configured to start clients automatically. When the user logs out, XDM resets the terminal for the next session. The following subsections describe XDM in more detail.

For hosts or networks on which XDM is not available, users can log in through the NCD Terminal Emulator (ncdterm). Using the NCD Terminal Emulator to log in is described in the NCDware User's Guide, and managing the terminal emulator is described in the NCDware System Administrator's Guide for UNIX Systems. Advanced configuration and management of the NCD Terminal Emulator are described in this manual in Chapter 12, Configuring the NCD Terminal Emulator.

Components of XDM

XDM consists of both host and terminal software:

• Hosts (called managers) that run the xdm daemon and offer login services
  

• NCD terminals that run XDMCP (X Display Management Control Protocol)
  

Terminals send XDMCP queries requesting display management, and hosts respond to terminal queries.

On XDM manager hosts, configuration files control how XDM works. The X11R5 and X11R6 versions of XDM provide the chooser program, which can be configured to display a choice of login hosts on the terminal.

XDMCP Queries and Host Responses

An NCD terminal can send three different types of queries. Depending upon the type of query and the host and terminal configuration, either a login banner or a Login Chooser appears on the terminal.

The three types of terminal queries are:

• Broadcast query-the terminal sends a general query to the network for any host running XDM to answer
  

• Direct query-the terminal requests connection to a specific host
  

• Indirect query-the terminal requests connection to a specific host; this host may forward the request to another host, answer the request, or offer a list of hosts
  

Configuring terminal queries is described in the NCDware System Administrator's Guide for UNIX Systems.

XDM and the DISPLAY Variable

The DISPLAY environment variable identifies the terminal on which clients display their windows and must be available to all clients when they start. This variable is set automatically by XDM for clients started on the login host. You must, however, specify the DISPLAY variable for clients started on other hosts.

The NCD Login Chooser

The Login Chooser is an NCD local client (login). Using the login client, you can configure the terminal to offer a choice of login hosts to the user. After the user selects a host, the host displays a login banner, which requests the user's account name and password. You can also configure the terminal so the host displays a login banner immediately and does not offer a choice of hosts.

The NCD Display Manager

The NCD Display Manager (ncddm) works with XDM to provide environment variables to local clients that require this information. The environment variables set are the username, the user's home directory, and the UID and GID. The Display Manager is installed by ncdinstall; the terminal must be configured to use the Display Manager. For information on the Display Manager, see the System Administrator's Guide.