owner@Ubuntu-desktop:~$ xrandr -q
Screen 0: minimum 640 x 480, current 800 x 600, maximum 1024 x 768
default connected 800x600+0+0 0mm x 0mm
   800x600        61.0*
   640x480        60.0
   1024x768_60.00   59.4
owner@Ubuntu-desktop:~$ xrandr --output default --mode 1024x768
xrandr: cannot find mode 1024x768
owner@Ubuntu-desktop:~$