This is what I use daily, which goes through usual X11 driver rather than VGA BIOS, no root access needed:
xrandr --output LVDS1 --off
- If your display is not a built-in LCD screen, substitute
LVDS1 with relevant port from you see from plain
xrandr command without parameter. It is usually something along the line of
This doesn't "standby" the screen in a sense of DPMS-style power save however; it actually disable the specified video output, and detach it from your display server.
The side effect of this headless state is your "desktop" would shrink to the minuscule size; around 320x200 pixel; you can press PrintScreen key to see what it looks like. This probably won't work for your usability tests, so...
To prevent the shrinkage; add
--fb option to set the virtual "desktop" size after your video output is off:
xrandr --output LVDS1 --off --fb 1024x768
LVDS1 with the relevant output port, and
1024x768 with your current resolution.
Once your video output is disabled and virtual "desktop" size is all set, you can commence your tests.
At the time you would like to come back, re-enable your output:
xrandr --output LVDS1 --auto
LVDS1 with the relevant output port.
- This will set the output to default monitor-native resolution. If you would like to restore it to a specific resolution, substitute
--auto with something like
--mode 1024x768 (replace
1024x768 with your desired resolution).
P.S. My answer is tested on Debian 7.0 32-bit GNU/Linux system, Xorg 1.12.4 display server, Intel i915 graphics.