vijayp@ike:~$ xrandr --output HDMI1 --primary
In case you don't know what your display is called, just run "xrandr" on its own. This is what my laptop says:
vijayp@ike:~$ xrandr Screen 0: minimum 320 x 200, current 2880 x 1200, maximum 8192 x 8192 VGA1 disconnected (normal left inverted right x axis y axis) LVDS1 connected 1280x800+0+0 (normal left inverted right x axis y axis) 261mm x 163mm 1280x800 60.0*+ 1024x768 60.0 800x600 60.3 56.2 640x480 59.9 HDMI1 connected 1600x1200+1280+0 (normal left inverted right x axis y axis) 367mm x 275mm 1600x1200 60.0*+ 1280x1024 75.0 60.0 1152x864 75.0 1024x768 75.1 60.0 800x600 75.0 60.3 640x480 75.0 60.0 720x400 70.1 DP1 disconnected (normal left inverted right x axis y axis)
