How to start the Gnome screen saver immediately
The command to start the Gnome screensaver is:
I tried to make this happen using keyboard shortcuts first, but couldn’t find a way. So I went with the next best thing: a launcher in the Gnome panel.
Right click the Gnome panel and click “Add to panel...”. Pick “Custom Application Launcher”. Another window appears. Fill it like this:
Type: Application Name: Screensaver Command: gnome-screensaver-command -a Icon: <pick any icon...>
Hit OK and now you can start the screensaver by clicking the new icon.