How to Create a macOS Big Sur ISO Disk Image

This post is more or less a reminder for myself how to create a macOS disk image. The created ISO image can be used with VM ware Fusion, VM ware Workstations, or used to make a bootable USB installer.

Download macOS Big Sur

macOS Big Sur elevates the most advanced desktop operating system in the world to a new level of power and beauty. Experience Mac to the fullest with a refined new design. Enjoy the biggest Safari update ever. Discover new features for Maps and Messages. And get even more transparency around your privacy.

First download macOS Big Sur from the Mac App Store. This is the only legal method to obtain a copy of the software. It’s a free download if you own a Mac, otherwise just barrow a friend or family-members Mac for a couple hours.

Create an Empty Disk Image

sudo hdiutil create \
  -o /tmp/macOS-Big-Sur \
  -size 16384 m \
  -volname macOS-Big-Sur \
  -layout SPUD \
  -fs HFS+J

Mount the Empty Disk Image

sudo hdiutil attach /tmp/macOS-Big-Sur.dmg \
  -moutpoint /Volumes/macOS-Big-Sur \
  -noverify

Copy Install Media to Mounted Disk Image

sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia \
  --volume /Volumes/macOS-Big-Sur \
  --nointeraction

Covert DMG to ISO and Rename Disk Image

hdiutil eject -force /Volumes/Install\ macOS\ Big\ Sur

hdiutil convert /tmp/macOS-Big-Sur.dmg \
  -o ~/Downloads/macOS-Big-Sur
  -format Unto

mv -v ~/Downloads/macOS-Big-Sur.cdr ~/Downloads/macOS-Big-Sur.iso

Remove Temporary Files

sudo rm -fv /tmp/macOS-Big-Sur.dmg