Using shared-folders in Virtual-Box (if your host operating system is Mac OS X and you have installed Ubuntu as the guest operating system.)

VirtualBox_SharedFolders.md

This will install the guest additions and is more or less equivalent to installing via the ISO,

sudo apt-get install virtualbox-guest-utils

Then,

sudo modprobe -a vboxguest vboxsf vboxvideo

After that,

sudo mount -t vboxsf VB-Shared /mnt/

Then you can access the shared files in the /mnt folder