To Setup screen saver in Ubuntu type in Terminal:
sudo apt-get remove gnome-screensaver
sudo apt-get install xscreensaver xscreensaver-data-extra xscreensaver-gl-extra
To configure your screensaver
After installation, perform a search in the Dash for Screensaver. Launch the Screensaver utility and use it to configure XScreenSaver and select your screensaver settings.
sudo apt-get remove gnome-screensaver
sudo apt-get install xscreensaver xscreensaver-data-extra xscreensaver-gl-extra
To configure your screensaver
After installation, perform a search in the Dash for Screensaver. Launch the Screensaver utility and use it to configure XScreenSaver and select your screensaver settings.