xrandr
Without external VGA:
> xrandr
Screen 0: minimum 320 x 200, current 1280 x 800, maximum 3840 x 1200
VGA disconnected (normal left inverted right x axis y axis)
LVDS connected 1280x800+0+0 (normal left inverted right x axis y axis) 331mm x 207mm
1280x800 60.0*+ 60.0 58.9
1024x768 60.0
800x600 60.3 56.2
640x480 59.9
TV disconnected (normal left inverted right x axis y axis)
With VGA in mirror mode:
> xrandr
Screen 0: minimum 320 x 200, current 1280 x 800, maximum 3840 x 1200
VGA connected 1280x800+0+0 (normal left inverted right x axis y axis) 376mm x 301mm
1280x800 60.0*+ 58.9
1280x960 60.0 60.0
1024x768 60.0
800x600 60.3 56.2
640x480 60.0 59.9
LVDS connected 1280x800+0+0 (normal left inverted right x axis y axis) 331mm x 207mm
1280x800 60.0*+ 60.0 58.9
1024x768 60.0
800x600 60.3 56.2
640x480 59.9
TV disconnected (normal left inverted right x axis y axis)