To begin, visit the site osboxes.org to download a virtual disk image for the Ubuntu version of Linux. While using Ubuntu is not required for the class, it will be easiest for those don't already have access to a Linux installation. When you visit the site, click on "VM Images" and select "VirtualBox Images":



This will take you to the main page for Virtual Box Images:




Scroll down on this page until you find the entry for "Ubuntu" and then click on it:




This will open up some additional text under the Ubuntu entry:





Click on "VirtualBox (VDI) image" to see a listing of all of the Ubuntu images available:



Scroll down until you find the Ubuntu 18.0.4 release area:




As shown in the image above, make sure that the "VirtualBox" tab is selected and then click on the "Download" button. You should get an archive file downloaded to your machine. On my Mac, it appears in the "Downloads" folder and will look something like this:

Then open the archive to unpack the disk image. Expanded, it can take up over 10GB of space so make sure you have enough room before proceeding. When unpacked on my Mac, I end up with the .vdi image in a folder named "64bit":



Remember where you unpacked the .vdi file! You will need it when creating your virtual machine.

Now that you have the .vdi file you can proceed with instructions on how to get VirtualBox for MacOS X, Windows or Linux!

And remember to configure Ubuntu once you have VirtualBox up and running on your machine!