GDM includes a graphical application that you can use to configure GDM. The following steps document how to disable remote login with this application:
To disable remote login
- 
Run /usr/bin/gdmsetup.
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Click the XDMCP tab.
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Verify that the Enabled XDMCP is not selected.
 
Note: Whether modifying the GDM configuration manually or by using /usr/bin/gdmsetup, you must restart GDM.