Cannot change built in display resolution (Ubuntu 16.04)

 I have been frustated since I was not able to setup built in resolution in my Ubuntu 16.04,

it was stuck to 800x600 pixel.

I have tried to change the resolution by following this tutorial, but it did not work.

https://askubuntu.com/questions/1075157/unable-to-set-my-screen-resolution-higher

and finally  I found the solution by following below tutorial :

https://askubuntu.com/questions/441040/failed-to-get-size-of-gamma-for-output-default-when-trying-to-add-new-screen-res

 in short the solution is to change the following line in the grub file :

#GRUB_GFXMODE=640x480

I change it to 1920 x 1080 for the resolution and remove the # :

GRUB_GFXMODE=1920x1080

And after that update the grub and reboot the server.

sudo update-grub

sudo reboot