Convert the macOS Beta Installer to an ISO Image


As a cautious explorer, you may want to try out the newly released Developer Preview of macOS Monterey while keeping your production installation safe; it is a preferable choice to run the beta in a VM.

However, since most hypervisors recognize only an ISO image, and not the “Install macOS” bundle provided by Apple, as the installation source, it is necessary to convert the app bundle to a disk image.

The process can be done within the following steps, which essentially (a) create an empty disk image, (b) prepare it as an installation media (as you’d do with a physical drive), and (c) convert it to the ISO format.

  1. Create an empty DMG image:
    hdiutil create -o /tmp/macOS12 -size 12000m -volname macOS12 -layout SPUD -fs HFS+J
  2. Mount the DMG:
    hdiutil attach /tmp/macos12.dmg -noverify -mountpoint /Volumes/macos12
  3. Write to the DMG with createinstallmedia
    sudo /Applications/Install\ macOS\ 12\ --volume /Volumes/macos12 --nointeraction
  4. [Easy to forget but necessary for proceeding] Unmount the DMG:
    hdiutil detach /Volumes/macos12
  5. Convert DMG to CDR:
    hdiutil convert /tmp/macos12.dmg -format UDTO -o ~/Downloads/macos12.cdr
  6. Convert (essentially rename) CDR to ISO:
    mv ~/Downloads/macos12.cdr ~/Downloads/macos12.iso

You may want to free disk space by removing the temporary disk image created during the creation process: rm /tmp/macos12.dmg or moving it to another location for archiving.



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