There’s more than one reason why you might want to create a macOS Big Sur ISO file. You may want to install macOS in virtual machines like VMWare and Parallels Desktop for extensive testing. Maybe you are ready to create alternate installation media on an external hard drive. Whatever your reason for creating a macOS Big Sur ISO file, you’d be happy to know that it’s possible to fine-tune a fully functional ISO file without having to use any third-party tool. If you are ready, let me guide you!

Create a macOS Big Sur ISO file using the Terminal app

So, how to get an ISO file on Mac? Thanks to the built-in application called Terminal, you can create an ISO file that can be used via the command line. For people wondering why the whole process requires the need for a terminal or third-party app, it’s because the macOS installer app is actually an .app file (and not a disk image).

It’s worth pointing out that you can also use the same process to create an ISO file for previous generations of macOS like macOS Catalina and Mojave. So even if you want the file for older generations of macOS, the following steps can guide you. That said, let’s go!

  1. To get started, go to Mac App Store and download the installer app for macOS Big Sur. Once the macOS installer app (named macOS Big has been downloaded, you can find it in the Apps case.

2. Now open the Terminal application. You can launch it from the Apps > Utilities case. Alternatively, you can press Command+Space and search for it terminal app to find it quickly.

3. Next, it’s time to create a temporary disk image. Launch the terminal and run the following command.

hdiutil create -o /tmp/MacBigSur -size 12500m -volname MacBigSur -layout SPUD -fs HFS+J

4. Next you need to mount disk image:

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

5. Next, copy installation files to the disk image we just created using the createinstallmedia utility that is part of the macOS Installer app.

sudo /Applications/Install macOS Big Sur/Contents/Resources/createinstallmedia –volume /Volumes/MacBigSur –nointeraction

6. Now, press return then type the administrator password to authenticate. Now you have to wait for some time until the installer is created. Once the process is complete, you will need to unmount disk image volume.

hdiutil detach /Volumes/MacBigSur/

7. Next, convert the newly created macOS Installer disk image file in an ISO/CDR file. Now it will appear on the desktop.

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

8. Next, change file extension from .cdr to .iso.

mv ~/Desktop/MacBigSur.cdr ~/Desktop/BigSur.iso

That’s all we can say about it! You have successfully created a macOS Big Sur ISO file (named BigSur.iso) on your Mac.

Create macOS Big Sur ISO File with Terminal

This is how you can create a working ISO file using the Terminal app on your Mac. It is good that the proprietary application works reliably to create an ISO file because you don’t need to search for third-party software or even shell out any money. As someone who relies heavily on Terminal to do this, I have to say that you can count on the app to be up to the task more often than not.

While it’s also possible to convert dmg and CDR files to ISO using Disk Utility, the whole process doesn’t seem straightforward. Therefore, I do not recommend it. By the way, do you have any questions or comments? Be sure to share your thoughts on this topic. Also, be sure to read our coverage of other macOS Big Sur articles, including our collection of the best Big Sur widgets, how to fix battery drain on Big Sur, and more.