To disable remote login
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Open the KDM configuration file for editing.
Typically, this file is located at /etc/X11/xdm/xdm-config or /usr/share/config/kdm/kdmrc on Redhat.
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Look for the [XDMCP] section and verify that the Enable property is either not present, commented out, or is set to false, like this:
[XDMCP] Enable=false.