Isso funcionou para mim
kj@n36l:~$ xrandr -q
Screen 0: minimum 320 x 200, current 1024 x 768, maximum 4096 x 4096
DVI-0 connected 1024x768+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
1024x768 60.00*
800x600 60.32 56.25
848x480 60.00
640x480 59.94
DVI-1 connected 1024x768+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
1024x768 60.00*
800x600 60.32 56.25
848x480 60.00
640x480 59.94
kj@n36l:~$ xrandr --output DVI-0 --primary --left-of DVI-1