Downloading older OS installers on incompatible hardware using VMs

A lot of Mac admins need to test software in their environment against both the shipping version of macOS and older versions of OS X. However, getting older OS installers from the Mac App Store (MAS) can be problematic if the Mac you’re using isn’t able to run the older OS as its own operating system. If the Mac you’re using isn’t itself able to run the older OS, a request to download the OS installer from the MAS will result in an error message like the one shown below.

If you’re in this situation, but also have VMware Fusion or a similar virtualization solution available, there is a way to download the desired older OS installer using a VM running the shipping version of macOS. For more details, see below the jump.