Попробуйте, после ключа -o указать подключенное устройство.
username@host: ~ xrandr
Screen 0: minimum 320 x 200, current 1440 x 900, maximum 8192 x 8192
LVDS1 connected 1440x900+0+0 (normal left inverted right x axis y axis) 304mm x 190mm
1440x900 60.26*+ 59.89 50.06
1360x768 59.80 59.96
1152x864 60.00
1024x768 60.00
800x600 60.32 56.25
640x480 59.94
VGA1 disconnected primary (normal left inverted right x axis y axis)
HDMI1 disconnected (normal left inverted right x axis y axis)
username@host: ~ xrandr -o LVDS1 left