How to Convert a MacOS Installer to ISO

Jul 20, 2020 - 25 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” or “Install MacOS” 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\ --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.


Related articles:

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


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  1. Bjorn says:

    Hi Paul – thanks for your article – works for Ventura as well, allthough, as mentioned by others, you need 6gb more in your dmg, so I used 15500m to be on the safe side.

    As for the claim that you can do this with Disk Utility, I strongly doubt you can – Apple make GUIs for the average user, not for this kind of thing. Mr “…” probably saw that “you can mount and unmount stuff in the GUI”, and forgot that there are quite a few operations besides that.

    Anyways – really good stuff – keep up the good work!

  2. Chris says:

    For Ventura (OS 13):

    Note: changed the working path to /Users/Shared

    mkdir /Users/Shared/custom_iso

    hdiutil create -o /Users/Shared/custom_iso/ventura -size 15000m -volname ventura -layout SPUD -fs HFS+J

    hdiutil attach /Users/Shared/custom_iso/ventura.dmg -noverify -mountpoint /Volumes/ventura

    /Applications/Install\ macOS\ –volume /Volumes/ventura –nointeraction

    hdiutil detach /Volumes/Install\ macOS\ Ventura

    hdiutil convert /Users/Shared/custom_iso/ventura.dmg -format UDTO -o /Users/Shared/custom_iso/ventura.cdr

    mv /Users/Shared/custom_iso/ventura.cdr /Users/Shared/custom_iso/ventura.iso

  3. Poetnerd says:

    Alas, following this procedure gave me a DVD that spun for half an hour but never booted. I was working with El Capitan for a 2009 13 inch MacBook Pro I was preparing to donate. I wanted to ship a bootable install DVD with it, but no joy.
    I used WinData DVD+R DL, and the burn said it was good and verified. But it simply would not boot.

  4. L33t haxor says:

    For Monterey, got an error in step 6 that the volume wasn’t big enough.
    Got it to work by deleting the temp file and repeating steps 4 & 5 with “14500m” instead of “8500m”.

  5. Stu says:

    This is exactly what I have been looking for! However when I tried to create a Catalina disc, it says the ISO is too big to fit on my DVD (I’m using dual layer)… any way of shrinking it down?

  6. JM says:

    I have tried this several times: 2x using as stated method, 1x using the Selby method. Either way, when, at Step 6, createinstallmedia tries to erase the disk it fails: “Error erasing disk error number (22, 0)”

    Any suggestions?


    • miatch says:

      I will get this same error or an error like “hdiutil: couldn’t unmount “disk2″ – Resource busy” every so often and haven’t quite yet figured out why. My work around is just to open disk utility or find it on the desktop and manually detach it.

    • Mark J says:

      I had this same very opaque error. I fixed it by increasing the size in step 4. After a few tries, I found 10000m worked for me. I’m not sure why my Mojave (downloaded 2021-09-29) required so much more space than the author’s.

  7. Carlos says:

    Created a High Sierra ISO file. It seems it worked with Sebby tip and your instructions.Thanks!!

  8. mark m says:

    Interesting article and worked great for me with Mojave!

    I’m guessing I am much less tech savvy than the average reader on your site. But the articles really help me understand the MacOS and fix issues or make changes!

    One question on this walkthough. In step #4 you Create a disk image DMG file that you later mount to create the installer app on and then you unmount the disk image.

    My question is when you finish is that original disk image file created in step 4 removed (/tmp/Mojave) or does it stay around somewhere in some temp folder? Don’t want to leave files or folders around to clutter up things and confuse me later when I run across them.

    Sorry if this is an obvious one to most folks here.


    • Paul says:

      Great question. Temp files (/tmp/) are quite literally temporary and will vanish automatically upon the next system reboot, you generally don’t want to interfere with /tmp files on your own as it can cause unexpected behavior and problems with system functionality, and in newer versions of Mac OS it’s locked down anyway.

      If interested you can read more about temporary user files and system files here:

      Glad you were able to make a macOS Mojave ISO file and that you find the articles useful!

  9. Toby Martin says:

    Thanks for the instructions – I had to make a few adjustments to get the latest 10.15.7 Catalina to shove itself into an .iso – Remove OS X everywhere and replace it with macOS, and then make the second .cdr bigger. The 10800 is a guess, but it works.

    hdiutil attach /Applications/Install\ macOS\ -noverify -mountpoint /Volumes/Catalina
    hdiutil create -o /tmp/CatalinaBase.cdr -size 9000m -layout SPUD -fs HFS+J
    hdiutil attach /tmp/CatalinaBase.cdr.dmg -noverify -mountpoint /Volumes/install_build
    asr restore -source /Applications/Install\ macOS\ -target /Volumes/install_build -noprompt -noverify -erase
    rm /Volumes/macOS\ Base\ System/System/Installation/Packages
    cp -R /Volumes/Catalina/Packages /Volumes/macOS\ Base\ System/System/Installation
    hdiutil detach /Volumes/macOS\ Base\ System
    hdiutil detach /Volumes/Catalina
    mv /tmp/CatalinaBase.cdr.dmg /tmp/BaseSystem.dmg

    hdiutil create -o /tmp/Catalina.cdr -size 10800m -layout SPUD -fs HFS+J
    hdiutil attach /tmp/Catalina.cdr.dmg -noverify -mountpoint /Volumes/install_build
    asr restore -source /Applications/Install\ macOS\ -target /Volumes/install_build -noprompt -noverify -erase
    cp /tmp/BaseSystem.dmg /Volumes/macOS\ Base\ System
    hdiutil detach /Volumes/macOS\ Base\ System
    rm /tmp/BaseSystem.dmg
    hdiutil convert /tmp/Catalina.cdr.dmg -format UDTO -o /tmp/Catalina.iso
    mv /tmp/Catalina.iso.cdr ~/Desktop/Catalina.iso
    rm /tmp/Catalina.cdr.dmg

  10. 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.

  11. 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.

  12. 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’!

  13. 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

  14. 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.


  15. ... 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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