rsi@evey ~ $ xrandr -q
Screen 0: minimum 320 x 200, current 3840 x 1200, maximum 8192 x 8192
VGA1 connected 1920x1200+0+0 (normal left inverted right x axis y axis) 518mm x 324mm
   1920x1200      60.0*+
   1920x1080      60.0  
   1600x1200      60.0  
   1680x1050      60.0  
   1280x1024      60.0  
   1440x900       59.9  
   1280x960       60.0  
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        60.0  
HDMI1 connected 1920x1200+1920+0 (normal left inverted right x axis y axis) 518mm x 324mm
   1920x1200      60.0*+
   1600x1200      60.0  
   1680x1050      60.0  
   1280x1024      60.0  
   1440x900       59.9  
   1280x960       60.0  
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        60.0  
DP1 disconnected (normal left inverted right x axis y axis)
HDMI2 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)

rsi@evey ~ $ xrandr --output HDMI1 --primary

Um beim Systemstart den Anschluss als primär zu setzen kann ein Startup Program eingerichtet werden ( Startup Applications → Add)