Apple is not providing an OS X El Capitan iso image – not even for sale, as far as I can tell. Although they do allow download of the full installer app from the App Store.
I’m using these 2 resources to understand the makeup of the downloaded installer app and to create an ISO or bootable USB from it.
-
[How to make a bootable OS X 10.11 El Capitan installer drive Macworld](http://www.macworld.com/article/2981585/operating-systems/how-to-make-a-bootable-os-x-10-11-el-capitan-installer-drive.html) - HOW TO: Create a bootable El Capitan ISO fo VMware - OSx86 10.11 (El Capitan) - InsanelyMac Forum
This worked:
``` #!/bin/bash
# Mount the installer image hdiutil attach /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/SharedSupport/InstallESD.dmg -noverify -nobrowse -mountpoint /Volumes/install_app
# Create the ElCapitan Blank ISO Image of 7316mb with a Single Partition - Apple Partition Map hdiutil create -o /tmp/ElCapitan.cdr -size 7316m -layout SPUD -fs HFS+J
# Mount the ElCapitan Blank ISO Image hdiutil attach /tmp/ElCapitan.cdr.dmg -noverify -nobrowse -mountpoint /Volumes/install_build
# Restore the Base System into the ElCapitan Blank ISO Image asr restore -source /Volumes/install_app/BaseSystem.dmg -target /Volumes/install_build -noprompt -noverify -erase
# Remove Package link and replace with actual files rm /Volumes/OS\ X\ Base\ System/System/Installation/Packages cp -rp /Volumes/install_app/Packages /Volumes/OS\ X\ Base\ System/System/Installation/
# Copy El Capitan installer dependencies cp -rp /Volumes/install_app/BaseSystem.chunklist /Volumes/OS\ X\ Base\ System/BaseSystem.chunklist cp -rp /Volumes/install_app/BaseSystem.dmg /Volumes/OS\ X\ Base\ System/BaseSystem.dmg
# Unmount the installer image hdiutil detach /Volumes/install_app
# Unmount the ElCapitan ISO Image hdiutil detach /Volumes/OS\ X\ Base\ System/
# Convert the ElCapitan ISO Image to ISO/CD master (Optional) hdiutil convert /tmp/ElCapitan.cdr.dmg -format UDTO -o /tmp/ElCapitan.iso
# Rename the ElCapitan ISO Image and move it to the desktop mv /tmp/ElCapitan.iso.cdr ~/Desktop/ElCapitan.iso ```