Linux GUI resolution on Hyper-V VM.

Recently I decided to give the Windows virtualization tool Hyper-V a try.
Debian became my OS of choice for the test.

All went well, until I booted into the GUI.  The gues OS window was 1/3rd of the whole screen.

So, here is one way to fix it :

Open the file /etc/default/grub with your favorite text editor (vi for example).

Find the line :

GRUB CMDLINE LINUX_DEFAULT="quiet"

and change it to :

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash video=hyperv_fb:1920x1200"

 Just make sure that instead of 1920x1080 you type the desired resolution.

 Then run :

sudo update-grub 

The change will take effect after you reboot the guest OS.