How to change default display output on ubuntu
We use VGA output for default display on ubuntu,If you want to change it to HDMI you must to modify /etc/X11/xorg.conf, and modify device section as shown below.
Section "Device" Identifier "i.MX Accelerated Framebuffer Device" Driver "vivante" Option "fbdev" "/dev/fb2" Option "vivante_fbdev" "/dev/fb2" Option "HWcursor" "false" EndSection
Then restart lightdm to make this configure work.
sudo /etc/init.d/lightdm restart
PS,i.mx6's ubuntu is not yet support dual display ,you can see discus on freescale's community https://community.freescale.com/thread/311751