19.2. Problems After Installation

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19.2.1. 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-compatible client, such as a network-connected workstation or X11 terminal. The procedure below explains how to enable XDMCP.

Procedure 19.3. Enabling XDMCP on IBM Z

  1. Open the /etc/gdm/custom.conf configuration file in a plain text editor such as vi or nano.
  2. In the custom.conf file, locate the section starting with [xdmcp]. In this section, add the following line:
  3. Save the file, and exit the text editor.
  4. Restart the X Window System. To do this, either reboot the whole system, or restart the GNOME Display Manager using the following command as root:
    # systemctl restart gdm.service
    Wait for the login prompt to appear again, and log in using your normal user name and password.
The IBM Z server is now configured for XDMCP. You can connect to it from another workstation (client) by starting a remote X session using the X command on the client workstation. For example:
$ X :1 -query address
Replace address with the host name of the remote X11 server. The command connects to the remote X11 server using XDMCP and displays the remote graphical login screen on display :1 of the X11 server system (usually accessible by pressing Ctrl-Alt-F8).
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 address with the host name of the remote X11 server:
$ Xnest :1 -query address
For more information about XDMCP, see the X Window System documentation at

19.2.2. Is Your System Displaying Signal 11 Errors?

A signal 11 error, commonly known as a segmentation fault, means that a program accessed a memory location that was not assigned to it. A signal 11 error can occur due to a bug in one of the software programs that is installed, or faulty hardware.
If you receive a fatal signal 11 error during the installation, first make sure you are using the most recent installation images, and let Anaconda verify them to make sure they are not corrupted. Bad installation media (such as an improperly burned or scratched optical disk) are a common cause of signal 11 errors. Verifying the integrity of the installation media is recommended before every installation.
For information about obtaining the most recent installation media, see Chapter 2, Downloading Red Hat Enterprise Linux. To perform a media check before the installation starts, append the boot option at the boot menu. See Section 23.2.2, “Verifying Boot Media” for details.
Other possible causes are beyond this document's scope. Consult your hardware manufacturer's documentation for more information.
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