Initiating Remote Login Sessions

Working with XServer typically includes the following steps:

1. Initiating a remote login session;
   
   
2. Starting a session manager. The first client run in a login session acts as the session manager. A useful session manager is 'xterm' or a window manager, both of which allow other clients to be run;
   
   
3. Running clients;
   
   
4. Completing the session with the session manager.

First of all a user should initiate a login session by using Telnet, XDMCP, or Startup (REXEC, RSH, RLOGIN) methods.

Note, a special case of working with clients is their starting from other X terminals without initiating remote login session on your PC. Clients have to be started with the option -display that defines your PC as a display.

The XDMCP Method

To use XDMCP, you have to run XSettings and preset the Use XDMCP check box to the enable state. You can use the XDMCP method only if you are sure that the host you want to connect to supports XDMCP and settings for XDMCP are correct there. (See section XDMCP Settings in Chapter Configuring WinaXe Plus.)

If you select the Broadcast XDMCP mode in the XDMCP Settings of XSettings, then the Select XDMCP Host window will appear after loading XServer. In this window, you will see the XDMCP hosts running on your network, and you can select one of them to start an X-session.

If you want to use the Query or Indirect XDMCP mode, you should specify the network node name or IP address for the host you want to connect to in the Connect Host field in the XDMCP Settings of XSettings.

After establishing the X connection, XDMCP contacts a 'xdm' process running on a host system. Then 'xdm' initiates login session as follows:

1. An optional authentication procedure takes place in which 'xdm' proves to the terminal that it is authorized to manage that display.
   
   
2. A session key is generated to be used for subsequent client authorization.
   
   
3. A username/password is requested to authenticate the user.
   
   
4. A session manager is run, typically /usr/lib/X11/xdm/Xsession, which is typically a shell script that ends up executing the required session manager such as 'xterm'.

When the session manager terminates, all other clients have their windows destroyed and should then terminate themselves. A new session is then initiated by 'xdm'.

Many XDMCP parameters may be redefined if required in /usr/lib/X11/xdm/xdm-config and /usr/lib/X11/xdm/Xresources. See manual xdm(1) for details. In particular, sites may find it useful to tailor the login window greeting in Xresources to identify the host system:

xlogin*Login*namePrompt: CLIENTHOST login:

CLIENTHOST is replaced by the host name of the system running 'xdm'.

Note: You cannot use XDMCP through SSH because SSH provides tunneling only TCP packets (it does not provide tunneling UDP packets).

The Telnet Method

Although XDMCP is recommended for convenience, it may sometimes be necessary to start clients without it, such as when the host system software does not support XDMCP or does not have it configured correctly. In these cases, you can run clients by typing shell commands in the normal manner. To gain access to a shell, you must first log in to the host system, for example on a dumb terminal such as the system console. For convenience, WinaXe Plus has the Telnet virtual terminal network interface. Start the Telnet_SSH program, connect to a host and enter commands to start clients. (See Chapter Telnet_SSH.)

Note: the Telnet_SSH and XServer programs use the same Keyboard Definition file you specified.

REXEC, RSH and RLOGIN Methods

The REXEC, RSH and RLOGIN methods can be used for automating host access and X client startup with using the REXEC, RSH and RLOGIN protocols respectively. You can use the Startup program to enter a single command line and execute one on a host, or run a local startup file that will automatically start one or more X clients. If XServer has not been running, it will start.

In order to run Startup, your host system must support the REXEC, RSH or RLOGIN protocol. REXEC operations may be done either by direct access to a remote host or through one of the established SSH1/SSH2 protocol connections as well (by using the "Dynamic Port Forwarding" feature). (See Chapter Startup.)

Note: if you use Startup to start your XServer, and XDMCP is enabled, the program will switch off the XDMCP startup method. This will be done because the host XDM script will most likely run before your command or file.

The REXEC, RSH and RLOGIN session dialogs are quite similar. Each of them asks for a host name, user ID name, and command. In addition, REXEC needs to know a user password.

For RSH method, some hosts require your PC to be authorized before using RSH, as it does not require a password. On UNIX systems, you need to add your PC name to the /etc/hosts.equiv and $HOME/.rhosts files on your host.

Also, check the /etc/inetd.conf and /etc/services files on the host. The services file is a local source of information regarding each service available through the Internet. The services file must contain an entry for each service. The inetd.conf file contains a list of servers that 'inetd' invokes when it receives an Internet request over a socket.