There is an annoying bug in VirtualBox 4.2.12 that makes the virtual Ubuntu machine cannot display properly. After finishing the installation and reboot, it keeps telling me that Ubuntu have to run in low graphic mode and prevents me from loggin in Ubuntu desktop.

To fix this, there are two solutions. The first one is that you simply switch back to VirtualBox 4.2.10 and the problem will be gone. However, if you still want to experience the new version, you need to do some shell commands. After the error message appears, select Exit to console login or Run in low-graphics mode for just one session. In my case, both options take me to the shell login interface. Enter you username and password to login and execute these two commands for installing the patch.

$ sudo apt-get install fglrx
$ sudo reboot

The virtual machine will now reboot and the problem’s gone.