Este site ajudou , então eu digitei:
xrandr -q
q significa consulta, o que dá:
Screen 0: minimum 320 x 200, current 1680 x 1050, maximum 2960 x 1050
VGA connected 1680x1050+0+0 (normal left inverted right x axis y axis) 474mm x 296mm
1680x1050 60.0*+ 59.9
1280x1024 75.0 59.9
1280x960 59.9
1152x864 75.0 74.8
1024x768 75.1 70.1 60.0
832x624 74.6
800x600 72.2 75.0 60.3 56.2
640x480 75.0 72.8 66.7 60.0
720x400 70.1
LVDS connected 1280x800+0+0 (normal left inverted right x axis y axis) 331mm x 207mm
1280x800 60.2*+ 60.0 50.0
1280x768 60.0
1024x768 60.0
800x600 60.3
640x480 59.9
TV disconnected (normal left inverted right x axis y axis)
Agora posso:
xrandr --output LVDS --left-of VGA
E: