Working with a macOS El Capitan (10.11.1) ISO image is primarily done for setting up virtual machines (like VirtualBox or VMware) or reviving older Macs that cannot use modern recovery methods Obtaining the Image Apple typically provides the installer as a file, which is the standard format for real Mac hardware . To get a working ISO: Official Source : You can download the El Capitan installer directly from Apple Support Apple Support Conversion
hdiutil create -o /tmp/ElCapitan -size 8g -layout SPUD -fs JHFS+
If you need it for a VM – You can create a legitimate ISO yourself if you still have the Install OS X El Capitan.app file, using commands in Terminal or tools like createinstallmedia plus hdiutil.
