After the screen saver activates, or after I manually lock the screen via Ctrl+Alt+L, I see a blank black screen with just the date / time in the upper right corner. A few seconds after that, my HP flat screen monitor(s) lose the video signal and display ugly hopping "No Input Signal" boxes.
I'd like to keep the blank black screen (It's less distracting, consumes about as much power, and allows me to unlock faster, as the monitors don't have to re-sync), so Ubuntu should keep driving the video output while the screen is locked.
How can I configure this? I'm using Ubuntu 14.04.3 LTS with the Gnome Classic Fall-back. Graphics card is NVIDIA with the open source Nouveau driver, but I also see this with an external HP NL571AA USB graphics adapter.