Fix for tiny GDM login screen with hdpi monitor

Fix_for_tiny_GDM_login_screen_with_hdpi_monitor.txt

Upgraded my XPS 15 from F27 to F28.  The new GDM signon screen was very tiny.  If I logged out, the login screen would be normal size.

Here is the solution I found from my friend Google.

REF: https://askubuntu.com/questions/906797/scaling-gnome-login-screen-on-hidpi-display

Make a backup of this xml file:

  sudo cp /usr/share/glib-2.0/schemas/org.gnome.desktop.interface.gschema.xml /usr/share/glib-2.0/schemas/org.gnome.desktop.interface.gschema.xml.bak0

  Edit the xml file:
  
    vi /usr/share/glib-2.0/schemas/org.gnome.desktop.interface.gschema.xml'

  Change the default value to 2 (or your desired scale factor):

    <key name="scaling-factor" type="u">
    <default>2</default>
    
  Be sure to run the next command and ignore all the messages.

   sudo glib-compile-schemas /usr/share/glib-2.0/schemas
   
 Rebooted XPS 15 and the GDM login screen was now readable and what I expected.