For some reason this has been disabled, or better impossible to do.
You need to edit in
/etc/sysconfig…the file “displaymanager”
## Path: Desktop/Display manager
## Description: settings to generate a proper displaymanager config
## Type: string(kdm,kdm3,kdm4,xdm,gdm,wdm,entrance,console)
## Default: ""
#
# Here you can set the default Display manager (kdm/xdm/gdm/wdm/entrance/console).
# all changes in this file require a restart of the displaymanager
#
DISPLAYMANAGER="kdm"
## Type: yesno
## Default: no
#
# Allow remote access (XDMCP) to your display manager (xdm/kdm/gdm). Please note
# that a modified kdm or xdm configuration, e.g. by KDE control center
# will not be changed. For gdm, values will be updated after change.
# XDMCP service should run only on trusted networks and you have to disable
# firewall for interfaces, where you want to provide this service.
#
DISPLAYMANAGER_REMOTE_ACCESS="no"
## Type: yesno
## Default: no
#
# Allow remote access of the user root to your display manager. Note
# that root can never login if DISPLAYMANAGER_SHUTDOWN is "auto" and
# System/Security/Permissions/PERMISSION_SECURITY is "paranoid"
#
**DISPLAYMANAGER_ROOT_LOGIN_LOCAL="yes"
## Type: yesno
## Default: yes
#
# Let the displaymanager start a local Xserver.**
DISPLAYMANAGER_ROOT_LOGIN_REMOTE="no"
## Type: yesno
## Default: yes
#
# Let the displaymanager start a local Xserver.
# Set to "no" for remote-access only.
# Set to "no" on architectures without any Xserver (e.g. s390/s390x).
#
DISPLAYMANAGER_STARTS_XSERVER="yes"
## Type: yesno
## Default: no
#
# TCP port 6000 of Xserver. When set to "no" (default) Xserver is
# started with "-nolisten tcp". Only set this to "yes" if you really
# need to. Remote X service should run only on trusted networks and
# you have to disable firewall for interfaces, where you want to
# provide this service. Use ssh X11 port forwarding whenever possible.
#
DISPLAYMANAGER_XSERVER_TCP_PORT_6000_OPEN="no"
## Type: string
## Default:
#
# Define the user whom should get logged in without request. If string
# is empty, display standard login dialog.
#
DISPLAYMANAGER_AUTOLOGIN="hase"
## Type: yesno
## Default: no
#
# Allow all users to login without password, but ask for the user, if
# DISPLAYMANAGER_AUTOLOGIN is empty.
#
DISPLAYMANAGER_PASSWORD_LESS_LOGIN="no"
## Type: yesno
## Default: no
#
# Display a combobox for Active Directory domains.
#
DISPLAYMANAGER_AD_INTEGRATION="no"
## Type: list(root,all,none,auto)
## Default: auto
#
# Determine who will be able to shutdown or reboot the system in kdm. Valid
# values are: "root" (only root can shutdown), "all" (everybody can shutdown),
# "none" (nobody can shutdown from displaymanager), "auto" (follow
# System/Security/Permissions/PERMISSION_SECURITY to decide: "easy local" is
# equal to "all", everything else is equal to "root"). gdm respects the
# PolicyKit settings for ConsoleKit. Shutdown configuration can be done via
# the polkit-default-privs mechanism.
#
DISPLAYMANAGER_SHUTDOWN="auto"
## Type: string
## Default: ""
#
# Mode to configure on output devices by default
# (RANDR 1.2 compatible drivers only).
#
# If set to "auto", DISPLAYMANAGER_RANDR_MODE_auto is used on laptops, and
# the empty string on workstations.
#
# The output is not explicitly enabled (read: disabled) if set to an empty
# string.
# If the variable contains a fully configured modeline (see default of
# DISPLAYMANAGER_RANDR_MODE_auto), the mode is defined and set.
# If the variable contains a mode name only, the mode has to be defined
# already.
#
# If a monitor is attached during Xstartup, or when invoking "xrandr --auto"
# during runtime, the output is correctly configured and a mode is
# automatically selected if none has been used so far.
#
# Variables are checked according to their extension for
# VGA DVI_I DVI_D DVI_A Composite S_Video Component LFP Proprietary
#
DISPLAYMANAGER_RANDR_MODE_VGA=""
#DISPLAYMANAGER_RANDR_MODE_DVI_I=""
#DISPLAYMANAGER_RANDR_MODE_DVI_D=""
#DISPLAYMANAGER_RANDR_MODE_DVI_A=""
#DISPLAYMANAGER_RANDR_MODE_Compsite=""
#DISPLAYMANAGER_RANDR_MODE_S_Video=""
#DISPLAYMANAGER_RANDR_MODE_Component=""
#DISPLAYMANAGER_RANDR_MODE_LFP=""
#DISPLAYMANAGER_RANDR_MODE_Proprietary=""
## Type: string
## Default: "1024x768_60 64.11 1024 1080 1184 1344 768 769 772 795 -HSync +Vsync"
#
# Mode to use for laptops for DISPLAYMANAGER_RANDR_MODE_* on laptops only,
# when the according variable is set to "auto".
# (RANDR 1.2 compatible drivers only).
#
DISPLAYMANAGER_RANDR_MODE_auto="1024x768_60 64.11 1024 1080 1184 1344 768 769 772 795 -HSync +Vsync"
## Type: string(Xorg)
## Path: Desktop/Display manager
## Default: "Xorg"
#
DISPLAYMANAGER_XSERVER="Xorg"
## Path: Desktop/Display manager
## Description: settings to generate a proper displaymanager config
## Config: kdm3
## Type: string
## Default:
#
# space separated list of users for which icons should be shown in KDM
# if empty, then take system defaults
#
KDM_USERS=""
## Type: string
## Default:
#
# Special greeting words in kdm
#
KDM_GREETSTRING=""
## Type: string
## Default:
#
# Defines extra Server Arguments given to the kdm display manager when
# starting a local display. Useful to override e.g. the -dpi setting.
#
DISPLAYMANAGER_KDM_LOCALARGS=""
## Type: string
## Default: SUSE
#
# Define the theme to be used by kdm. If empty, the traditional login
# window is used (which lacks some features)
#
DISPLAYMANAGER_KDM_THEME="SUSE"
Make sure you save the original !!!
Cheers