# Create a blank temporary disk image container hdiutil create -o /tmp/ElCapitan.cdr -size 7316m -layout SPUD -fs HFS+J # Mount the temporary disk container hdiutil attach /tmp/ElCapitan.cdr.dmg -noverify -nobrowse -mountpoint /Volumes/install_build # Mount the official Apple Core Installation Disk Image hdiutil attach /Applications/Install\ OS\ X\ El\ Capitan.app/Contents/SharedSupport/InstallESD.dmg -noverify -nobrowse -mountpoint /Volumes/install_app # Restore the base system structure onto your temporary container asr restore -source /Volumes/install_app/BaseSystem.dmg -target /Volumes/install_build -noprompt -noverify -erase # Unlink the generic packages placeholder and swap in the actual installation files rm /Volumes/OS\ X\ Base\ System/System/Installation/Packages cp -rp /Volumes/install_app/Packages /Volumes/OS\ X\ Base\ System/System/Installation/ # Unmount both active disk volumes hdiutil detach /Volumes/OS\ X\ Base\ System hdiutil detach /Volumes/install_app # Convert the finalized .cdr format into a globally compatible .iso image hdiutil convert /tmp/ElCapitan.cdr.dmg -format UDTO -o ~/Desktop/ElCapitan.iso Use code with caution. Option B: Downloading Verified Pre-Built Images
(Replace /dev/sdX with your USB drive’s device identifier.) macosxelcapitan10111imageiso work
Alternatively, you can convert the downloaded .dmg file to an ISO with a simpler two-step process: # Create a blank temporary disk image container
Allocate at least 4GB of RAM and 2 CPUs for better performance. macosxelcapitan10111imageiso work