How to Convert a MacOS Installer to ISO

Jul 20, 2020 - 9 Comments

macOS installer ISO

Advanced Mac users may wish to convert a MacOS Installer application into an ISO file. Typically the resulting installer ISO files are used for installing macOS into virtual machines like VMWare or VirtualBox, but they can also be used to burn the ISO to media to create a boot disk. This offers an alternative to creating a bootable USB flash drive for MacOS installers as well.

This tutorial will walk through the steps to create an ISO file of a MacOS installer.


In this particular walkthrough, we’ll be converting a MacOS Mojave installer application into an ISO file. You can use the same steps to create an ISO file from practically any other MacOS Installer with createinstallmedia present however, including building a MacOS Catalina ISO, or for Big Sur, High Sierra, and Sierra, simply by replacing the file names where appropriate.

How to Create a MacOS Mojave ISO or Catalina ISO File from an Installer

This process will take an installer for macOS and create an ISO file from it which can be booted or used as a typical disk image file.

  1. First, download MacOS Mojave installer, or the MacOS Catalina installer (or the installer you wish to turn into an ISO) from the Mac App Store
  2. When the “Install MacOS Mojave.app” or “Install MacOS Catalina.app” application is fully downloaded and within the /Applications folder, proceed
  3. Next, open the Terminal application
  4. Create a disk image DMG file buy issuing the following command:
  5. hdiutil create -o /tmp/Mojave -size 8500m -volname Mojave -layout SPUD -fs HFS+J

  6. Mount the created DMG disk image as follows:
  7. hdiutil attach /tmp/Mojave.dmg -noverify -mountpoint /Volumes/Mojave

  8. Next we will use createinstallmedia to create the macOS installer application on the mounted volume:
  9. sudo /Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/Mojave --nointeraction

  10. When createinstallmedia has finished, next you can unmount the volume you just created:
  11. hdiutil detach /volumes/Install\ macOS\ Mojave

  12. Now we convert the DMG disk image file to an ISO disk image file (technically a CDR file but it’s the same as an iso)
  13. hdiutil convert /tmp/Mojave.dmg -format UDTO -o ~/Desktop/Mojave.cdr

  14. Finally, we rename the CDR file extension to ISO to convert the CDR to ISO:
  15. mv ~/Desktop/Mojave.cdr ~/Desktop/Mojave.iso

That’s it, now you should have an “Mojave.iso” disk image file on the Mac desktop which is the macOS installer ISO image.

If you intend on using the ISO file for a virtual machine, you simply need to select the Mojave.iso disk image in the virtual machine app as a boot disk, or mount it within the VM as any other disk image would be. You can also convert ISO files to VDI VirtualBox images if needed.

ISO files are flexible and widely used, they can also be burned to create boot disks and to other media, and you can also copy the ISO to a USB drive with dd or perform any other multitude of actions.

Whether or not creating a macOS installer ISO file and using that ISO is easier than simply using a bootable USB flash drive is entirely a matter of use cases, and in some situations an ISO is the only usable format (ie for certain virtualization scenarios).

Were you successful in creating an ISO file from a macOS installer? Do you have another approach to make an ISO file for macOS installers? Let us know in the comments below.

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Posted by: Paul Horowitz in Command Line, Mac OS X, Tips & Tricks

9 Comments

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  1. Kurt Moedritzer says:

    I am one of your average Mac user and enjoy reading the OSCDaylies. However, this one (How to Convert a MacOS Installer to ISO) is beyond me. What is ISOfile, VMWare, MDM, Virtual Box?

    For the millions of Mac users please define these terms when they are first used in this article. This is common practice in technical and scientific articles to help the readers. A potential approach would be to add footnotes.

  2. Sebby says:

    Too much work, I fancy. You can create an image, partition it and put a filesystem in it, in the right image format, all in one step:

    hdiutil create -size 10g -type UDTO -layout SPUD -fs JHFS+ ~/Desktop/something.cdr && open ~/Desktop/something.cdr

    … and then prepare the “media” using createinstallmedia, as you described it. That’s it–unmount the new installer, rename the cdr to an iso, and you’ve finished.

  3. Richard B says:

    In step #7 the ‘v’ in /volumes must be in upper-case for the detach command to work i.e., /Volumes
    Just sayin’!

  4. Mike Sanders says:

    I want to do this for Snow Leopard but when I download the dmg from the web I cannot open it in 10.15.6. I need this file to open a blocked older Mac

  5. Gregory F O'Hara says:

    Paul. I know its small but search your article for the word “buy”. You probably meant to use the word “by”. You might want to check your mask, it may be too tight!
    :)
    Thanks for the article.

    Greg

  6. ... says:

    Ummm guys, You can do the exact same thing with Disk Utility and then change the extension manually from CDR to ISO.

    • Paul says:

      Interesting, can you elaborate on how you would convert a macOS installer application into an ISO with Disk Utility? I haven’t seen that before.

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