If you installed or upgraded Ubuntu 14.04/14.10 in VirtualBox recently, you might have seen that the resolution of the display is very low, 640×80. To get pass this problem, you just need to do a simple tweak in the settings.
if you ran ‘xrandr’ command in the terminal, you would only see one resolution listed there. To change the resolution, first search Xdiagnose in dash or sudo Xdiagnose in terminal and start it. You might need to enter the admin password. Check all the 3 check-boxes under debug and click Apply.
Next search for Additional Drivers in the dash and start it. Choose Using x86 virutalization option and click apply. Enter your password and confirm it.
Now reboot Ubuntu and you will have a big resoltion. That’s it 😉 If you run xrandr command now in the terminal, you will see all the resolutions listed.
Ubuntu Low Screen Resolution