Comment 31 for bug 761830

@Eliah Kagan

The netboot image can be obtained through these URLs

http://cdimage.ubuntu.com/netboot/
http://archive.ubuntu.com/ubuntu/dists/natty/main/installer-amd64/current/images/netboot/mini.iso

Essentially it's a super stripped down installer (In this case around 22MB) that ensures an extremely fresh install.

http://psung.blogspot.com/2009/01/ubuntu-netboot-installers.html