There may be times when you don’t want the OS X login screen saver to kick in. This might apply when, for example, the screensaver engine (ScreenSaverEngin) is acting up, and you don’t want it to activate, ever.
![Cosmos screen saver NGC 3190](http://www.macobserver.com/wp-content/uploads/2016/07/Galaxy-NGC-3190b.jpg)
First. The activation of the normal screen saver in OS X, after you’ve logged in, is managed with System Preferences > Desktop & Screen Saver > Screen Saver. There, you can set it to the desired time on the bottom left where it says Start after: Or set to Never.
Login Screen
However, the screen saver that kicks in after a period of time at the login screen is not controlled by that user setting. Instead use this terminal command:
sudo defaults write /Library/Preferences/com.apple.screensaver loginWindowIdleTime NNNN
Where NNNN is the delay in seconds before it kicks in. (You’ll need to enter an Administrator password.) To stop the screen saver permanently, set NNNN = 0. That is,
sudo defaults write /Library/Preferences/com.apple.screensaver loginWindowIdleTime 0
I’m testing this myself because I’ve occasionally seen problems with my graphics card and the process called ScreenSaverEngin. In my case, it can cause a lock up when the login screen sits idle too long. Your need may be driven by a different reason.