os/x yosemity / el capitan  -  Anmeldebildschirm Screen Saver

To set which Screen Saver is used at the login screen you can use the following command which in this example choses the Computer Name aka. 'Message' Screen Saver.

/usr/bin/defaults write /Library/Preferences/com.apple.screensaver loginWindowModulePath "/System/Library/Frameworks/ScreenSaver.framework/Resources/Computer Name.saver"

For more details see these two Apple articles.


Managed Client: How to customize the Computer Name screen saver message for the login window - Apple Support
OS X: Configuring a screen saver to display at the login window - Apple Support


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