XDMCP Connections to Red Hat Linux 7.0 or Higher
Technical Note 1680
Last Reviewed 08-May-2009
Applies To
Reflection X Advantage
Reflection X version 14.x only
Red Hat Linux version 7.0 or higher
Red Hat Enterprise Linux version 4.0 or higher
Summary

Red Hat Linux versions 7.0 or higher include default security features that prevent Reflection X from establishing an XDMCP connection. This technical note details the steps required to configure Red Hat Linux to allow Reflection X XDMCP connections using the GNOME Display Manager (gdm), KDE Display Manager (kdm), or the XDM Display Manager (xdm). It also provides fixes or workarounds for font-related display manager and terminal client initialization difficulties.

About the X Display Manager

The X Display Manager provides a graphical replacement for the host's command line login prompt when users connect over the X Display Manager Control Protocol (XDMCP). Red Hat provides support for the Gnome Display Manager (gdm), the KDE Display Manager (kdm), and the X Display Manager (xdm). Each of these display managers can be configured to automatically start the GNOME or KDE X Windows System graphical desktop environment.

Modifying Red Hat Linux for XDMCP Connections

The following sections provide steps for configuring XDMCP connections using gdm, kdm, or xdm:

  • Using GNOME's GDM X Display Manager
  • Using KDE's KDM X Display Manager
  • Using the XDM X Display Manager

Instructions are also provided for defining or changing which desktop environment automatically starts after login: GNOME or KDE.

Note the following:

  • The steps required vary depending on the version of Red Hat. Follow the instructions based on the version of Red Hat you are running. If a step is not applicable to your version, skip to the next step.
  • You must be logged into your Red Hat Linux host as root to make these edits.

You can log on at either the host console or from your PC using the linux.rxc template provided with Reflection X, but you must be logged in as root to make the changes presented in this technical note. (Most Linux hosts do not allow you to log on as root remotely, therefore, if you use the linux.rxc template, first log on using a normal user account, and then use the su command at the xterm command prompt to log in as root.)

  • GNOME or KDE must be installed on your system prior to following these configuration steps, and these directions are based on the original versions of GNOME and KDE that ship with each revision of Red Hat Linux 7.0 - 9.0.

Using GNOME's GDM X Display Manager

To configure Red Hat Linux to use gdm and automatically start the GNOME desktop environment, follow the steps below.

  1. Edit the /etc/sysconfig/desktop file to define GNOME as the X desktop environment that loads on connection.
    1. Open the /etc/sysconfig/desktop file.
    2. Locate the DESKTOP= entry. Note: The entry may need to be created and it is case sensitive.

Change this setting to: DESKTOP="GNOME"

    1. Save the file.
  1. Edit the gdm.conf file.
    1. Open the /etc/X11/gdm/gdm.conf file.

Note: In Red Hat Enterprise Linux version 5, the path is /etc/gdm/custom.conf.

    1. Under the "[xdmcp]" heading, change the default "enable" entry:

In Red Hat version 7.0 - 7.1: change Enable=0 to Enable=1.

In Red Hat version 7.2 - 9.0: change Enable=false to Enable=true.

In Red Hat Enterprise Linux version 5: add Enable=true.

    1. Save the file.
  1. Initialize the Changes.

Stop gdm, xdm, and kdm by entering the following at the command prompt:

In Red Hat version 7.0 - 7.2: killall gdm xdm kdm

In Red Hat version 8.0 - or higher: killall gdm-binary xdm kdm

You should now be able to establish an XDMCP connection using Reflection X (the display manager will restart automatically when a connection is requested).

Additional GNOME Settings

  • By default, GNOME uses TTF fonts with antialiasing. Antialiasing is an effect applied to the edges of characters to make them look smooth. Reflection X does not support antialiasing. If you experience font-related issues, follow these steps to disable GNOME antialiasing.
    1. In GNOME, click Foot/Hat/System > Preferences > Font, and change the font setting to a common font. For example, Fixed, Courier, or Helvetica.
    2. In the Font Rendering box, select Monochrome. Monochrome is the only choice that disables antialiasing. Note: Monochrome font rendering may cause the edges of characters to appear jagged.
    3. Click Close.
  • Desktop background images can affect startup speed and the speed of windows opening and closing. If you are experiencing slow speeds in these areas, navigate to Font > Preferences > Background, and try changing your background to a solid color.

Using KDE's KDM X Display Manager

To configure Red Hat Linux to use kdm and automatically start the KDE desktop environment, follow the steps below.

  1. Edit the /etc/sysconfig/desktop file to define which X desktop environment loads on connection.
    1. Open the /etc/sysconfig/desktop file.
    2. Locate the DESKTOP= entry. Note: This entry may need to be created, and it is case sensitive.

For KDE desktop, change this entry to: DESKTOP="KDE"

    1. Save the file.
  1. Edit the Xaccess file.
    1. Open the /etc/X11/xdm/Xaccess file.

Note: In Red Hat Enterprise Linux version 5, the path is /usr/share/config/kdm/Xaccess.

    1. Verify that the following lines appear as shown below:
* #any host can get a login window
* CHOOSER BROADCAST #any indirect host can get a chooser

Note: The asterisk (*) symbol in front of each line makes the line active. If a pound (#) symbol appears on the line before the * symbol, delete the # symbol.

    1. Save the file.
  1. Edit the kdmrc file.
    1. Open the kdmrc file. (Depending on the version of Red Hat, this file may be located under /usr/share/config, /etc/kde/kdm, or /etc/X11/xdm.)
    2. Under the "[Xdmcp]" heading, change the default entry of Enable=false to Enable=true.

Note: In Red Hat Enterprise Linux version 5, this parameter is set to Enable=true by default.

    1. Save the file.
  1. In Red Hat version 7.0 - 7.1 and 8.0 - 9.0 only, edit the /etc/X11/xdm/xdm-config file.
    1. Open the /etc/X11/xdm/xdm-config text file.
    2. Comment out the requestPort command by inserting an exclamation point (!) in front of the command line, as shown below:
!DisplayManager.requestPort: 0
    1. Save the file.
  1. In Red Hat 8.0 - 9.0 only, edit the prefdm file.
    1. Open the /etc/X11/prefdm file.
    2. Locate the preferred= entry.
    3. Change this entry to: preferred=kdm.
    4. Save the file.
  2. Initialize the Changes.

Stop gdm, xdm, or kdm by entering the following at the command prompt:

In Red Hat 7.0 - 7.2: killall gdm xdm kdm

In Red Hat 8.0 - 9.0: killall gdm-binary xdm kdm

You should now be able to establish an XDMCP connection using Reflection X (the display manager will restart automatically when a connection is requested).

Using the XDM X Display Manager (Versions 7.0 - 9.0)

To configure Red Hat Linux 7.0 - 9.0 to use xdm and automatically start an X desktop environment, follow the steps below.

  1. Edit the /etc/sysconfig/desktop file to define which X desktop environment loads on connection.
    1. Open the /etc/sysconfig/desktop file.
    2. Locate the DESKTOP= entry. Note: This entry is case sensitive.

For the GNOME desktop, change this entry to: DESKTOP="GNOME"

For the KDE desktop, change this entry to: DESKTOP="KDE"

    1. Save the file.
  1. In Red Hat 7.0 - 7.2 only, edit the /etc/inittab file.
    1. Open the /etc/inittab file.
    2. Under the heading "# Run xdm in runlevel", insert a pound (#) at the beginning of the entry to comment out the current command. For example, the edit line should appear as follows
# x:5:respawn:/usr/bin/prefdm -nodaemon
    1. Under the heading "#Run xdm in runlevel", add the following command line:
x:5:respawn:/usr/bin/X11/xdm -nodaemon
    1. Save the file.
  1. In Red Hat 7.0 - 7.2 only, initialize the /etc/inittab changes.

Enter the following command at the UNIX prompt. This causes system to re-examine the inittab file:

/sbin/init q
  1. Edit the /etc/X11/xdm/Xaccess file.
    1. Open the /etc/X11/xdm/Xaccess file.
    2. Verify that the following lines appear as shown below.
* #any host can get a login window
* CHOOSER BROADCAST #any indirect host can get a chooser

Note: The asterisk (*) in front of each line makes that line active. If a pound (#) appears on the line before the * symbol, delete the # symbol because this # symbol comments out the command line.

    1. Save the file.
  1. Edit the /etc/X11/xdm/xdm-config file.
    1. Open the /etc/X11/xdm/xdm-config file.
    2. Comment out the requestPort command by inserting an exclamation point (!) in front of the command line, as shown below:
!DisplayManager.requestPort: 0
    1. Save the file.
  1. In Red Hat version 8.0 - 9.0 only, edit the prefdm file.
    1. Open the /etc/X11/prefdm file.
    2. Locate the preferred= entry.
    3. Change this entry to: preferred=xdm
    4. Save the file.
  2. Initialize the Changes.

Stop gdm, xdm, or kdm by entering the following at the command prompt:

In Red Hat 7.0 - 7.2: killall gdm xdm kdm

In Red Hat 8.0 - 9.0: killall gdm-binary xdm kdm

You should now be able to establish an XDMCP connection using Reflection X.

Related Technical Notes
1229 Troubleshooting XDMCP Connections to UNIX and Linux Hosts
9992 Reflection X Technical Notes

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