1) Create a blank disk image: hdiutil create -o /tmp/HighSierra.cdr -size 7316m -layout SPUD -fs HFS+J 2) Mount your image: hdiutil attach /tmp/HighSierra.cdr.dmg -noverify -nobrowse -mountpoint /Volumes/install_build 3) Restore BaseSystem.dmg from the installer: asr restore -source /Applications/Install\ macOS\ High\ Sierra.app/Contents/SharedSupport/BaseSystem.dmg -target /Volumes/install_build -noprompt -noverify -erase 4) Unmount the image: hdiutil detach /Volumes/OS\ X\ Base\ System 5) Convert the image you created into an ISO file: hdiutil convert /tmp/HighSierra.cdr.dmg -format UDTO -o /tmp/HighSierra.iso 6) Move the ISO to the desktop: mv /tmp/HighSierra.iso.cdr ~/Desktop/HighSierra.iso
