How to Convert a MacOS Installer to 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:

hdiutil create -o /tmp/Mojave -size 8500m -volname Mojave -layout SPUD -fs HFS+J

5. Mount the created DMG disk image as follows:

hdiutil attach /tmp/Mojave.dmg -noverify -mountpoint /Volumes/Mojave

6. Next we will use createinstallmedia to create the macOS installer application on the mounted volume:

sudo /Applications/Install macOS Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/Mojave --nointeraction

7. When createinstallmedia has finished, next you can unmount the volume you just created:

hdiutil detach /volumes/Install macOS Mojave

8. 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)

hdiutil convert /tmp/Mojave.dmg -format UDTO -o ~/Desktop/Mojave.cdr

9. Finally, we rename the CDR file extension to ISO to convert the CDR to ISO:

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.