As with the default installer, the alternate installer is downloaded in the form of an ISO image that we can use to create a bootable CD/DVD or flash drive. To download the alternate installer, visit the following website: http://cdimage.ubuntu.com/releases/18.04/release/

The file you're looking for should be named ubuntu-18.04-server-amd64.iso or similar (if there's a point release for example, it may be named ubuntu-18.04.x-server-amd64.iso where x is the point release number). The ISO image you download can be used in a virtual machine right away, or you can create a bootable media with which to install it on a physical machine. The process of creating a bootable flash drive was covered in Chapter 1, Deploying Ubuntu Server, so refer back to that if you need a refresher on using Etcher to create bootable install media.

Once you have the bootable media created, you're ready to begin. You'll boot your server with this media just as you would with the normal installer; the only difference in set up is which ISO image you're using.