The K Desktop Environment

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5. Using kdm, the KDE X Display Manager (optional).

5.1 Replacing xdm with kdm: the "kdm_on" script.

KDE provides an enhanced replacement (kdm) for the "X Display Manager" (xdm), which provides the X Window system login screen. For troubleshooting purposes, it is useful to know that kdm runs independently of the KDE desktop - the only connection is that the KDE desktop provides a graphical interface for configuring kdm.

In particular,

The KDE X Display Manager kdm in general uses the same configuration files as xdm; one exception is that kdm can be configured at compilation time to use its own configuration file for PAM (Pluggable Authentication Modules), Red Hat's password checking system, and this has been done in these RPM packages.

A (bash) shell script kdm_on is provided to edit two of the default Red Hat X Window system configuration files: /etc/inittab, (to make kdm the default X Display Manager in runlevel 5, instead of xdm), and /etc/X11/xdm/Xsetup_0 (to allow the background wallpaper of the X Window system login screen to be configurable from the KDE desktop). All the system administrator needs to do to make these changes is to type

kdm_on
A second shell script kdm_off is available if the system administrator wishes to reverse this (type "kdm_off") to again make xdm the default X Display manager. Both scripts save copies of the original files (as /etc/inittab.kdesave, /etc/X11/xdm/Xsetup_0.kdesave).

If you uninstall KDE, the kdm_off script is run as part of the uninstallation script of the kdesupport RPM package.

5.2 The kdm "shutdown" screen.

Unlike xdm, the kdm login screen has a "shutdown" button, that allows the system to be shut down. The kdm configuration initially installed by this RPM package allows system shutdown by any user, but the System Administrator can configure kdmin the KDE Control Center so a dialog box requiring the Root password opens when "shutdown" is pressed.

This dialog box presents three options:

If you wish to allow system shutdown without requiring the root password to be given, you (as root) can configure this using the KDE control center when the KDE Desktop is running.

The KDE Control Center (or the "K --> Settings" menu) has a graphical interface ("Applications --> Login Manager") for configuring kdm, including shutdown privileges. Selections "All" or "Console Only" in "allow to shutdown" on the "Sessions" screen, allows anyone to shut the system down without being prompted for a password. You can also do this manually by editing the kdm configuration file /opt/kde/share/config/kdmrc: just change the line "ShutdownButton=RootOnly" to "ShutdownButton=ConsoleOnly".

5.3 Configuring the login screen background (optional).

The change made to /etc/X11/xdm/Xsetup_0 by the kdm_on script allows the background wallpaper of the X Display Manager login screeen to be configured by the System Manager, using the "Applications --> Desktop Manager" selection in the KDE Control center.

However, if you prefer to keep the Red Hat login screen background (a banner saying "Red Hat Linux", with a picture of the Linux penguin logo ("Tux") in a red hat), edit /etc/X11/xdm/Xsetup_0 to delete the last line "/opt/kde/bin/kdmdesktop", which was added by the kdm_on script. (This will disable display of configurable backgrounds for the login screen).

5.4 Configuring kde's PAM service (optional)

Like Red Hat's xdm, kdm (and the KDE screensaver lock) uses the PAM (Pluggable Authentication Module) system for authenticating users (i.e. password checking). This will transparently handle shadow passwords, for example, and can be configured to use many different authentication schemes.

KDE's PAM service (called "kde") is configured by the file /etc/pam.d/kde. If this file does not exist, the kdebase RPM package installs a default version (a copy of the Red Hat default /etc/pam.d/xdm). If the kdebase RPM is uninstalled, and the kde PAM configuration file is different from this default file, it is saved as /etc/pam.d/kde.rpmsave.

Note that kdm (unlike Red Hat's xdm) implements "PAM session" support, so new PAM customizations are possible. See the PAM documentation in /usr/doc/pam-* to learn what you can do with PAM, and how to configure it with a customized /etc/pam.d/kde.

If /etc/pam.d/kde is deleted or corrupt, you will not be able to login under kdm (hopefully you can access the system through a console, in that case). A quick fix if this happens is for root to copy /etc/pam.d/xdm to /etc/pam.d/kde.

Even if you do not use kdm, the pam service "kde" should be configured, as it also provides password authentication services to kcheckpass, used by the KDE screen lock.

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