The last time I’ve tried to run Ubuntu 14.04.02 in VirtualBox, I got a very low screen resolution of 640×480, and xrandr was reporting it’s the only resolution available; not good because I could only use half of each window. This was the first time I came across this issue and don’t really care what caused it, but, searching around the web, I found various possible quick fixes, not of them actually working.
All you need to do is to install Guest Additions. That’s all! ;-)
How to fix VirtualBox and Ubuntu 14.04.2 low resolution (640×480) issue
1. First of all, boot Ubuntu in the VirtualBox, enter username/password in login window.
2. Go to (VirtualBox) Devices – Insert Guest Additions CD image..
3. Confirm what you want to do
4. Enter your password
5. Wait for installation
6. Reboot Ubuntu and enjoy!