Ubuntu guest resolution issues on virtualbox with Mac host

If you get blank screen with just a cursor on Ubuntu, probably it’s due to lightdm issues with systems running on SSD.

come out of the blank screen by: CTRL + ALT + F1

use gdm instead of lightdm: sudo apt-get install gdm

if gdm already installed: sudo dpkg-reconfigure gdm

I got full resolution on mac after installing Virtualbox drivers that popped up in Additional Drivers. After that I had to mount the VBOX Guest additions ISO from devices menu and restart for the changes to take effect.

Ref: http://www.webupd8.org/2013/01/ubuntu-lightdm-black-screen-when-using.html