24.3. Problems After Installation

24.3.1. Remote Graphical Desktops and XDMCP

If you have installed the X Window System and would like to log in to your Red Hat Enterprise Linux system using a graphical login manager, enable the X Display Manager Control Protocol (XDMCP). This protocol allows users to remotely log in to a desktop environment from any X Window System compatible client (such as a network-connected workstation or X11 terminal).
To enable remote login using XDMCP, edit the /etc/gdm/custom.conf file on the Red Hat Enterprise Linux system with a text editor such as vi or nano. In the [xdcmp] section, add the line Enable=true, save the file, and exit the text editor.
To enable this change, you will need to restart the X Window System. First, switch to runlevel 4:
/sbin/init 4
The graphical display will close, leaving only a terminal. When you reach the login: prompt, enter your username and password.
Then, as root in the terminal, switch to runlevel 5 to return to the graphical interface and start the X11 server:
/sbin/init 5
From the client machine, start a remote X11 session using X. For example:
X :1 -query s390vm.example.com
The command connects to the remote X11 server via XDMCP (replace s390vm.example.com with the hostname of the remote X11 server) and displays the remote graphical login screen on display :1 of the X11 server system (usually accessible by using the Ctrl-Alt-F8 key combination).
You can also access remote desktop sessions using a nested X11 server, which opens the remote desktop as a window in your current X11 session. Xnest allows users to open a remote desktop nested within their local X11 session. For example, run Xnest using the following command, replacing s390vm.example.com with the hostname of the remote X11 server:
Xnest :1 -query s390vm.example.com