If upgrading, you must be on OS X 10.6.8 (Snow Leopard) or later. How to Get a Working ISO Image
To summarize the working formula:
: Automatically positions two apps side-by-side to fill the screen. macosxelcapitan10111imageiso work
hdiutil create -o /tmp/ElCapitan -size 8000m -volname ElCapitan -layout SPUD -fs HFS+J If upgrading, you must be on OS X 10
While Apple primarily distributes its operating systems through the Mac App Store, finding older versions like 10.11.1 can be tricky if they aren't in your "Purchased" history. macosxelcapitan10111imageiso work