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How to Install macOS 11 "Big Sur" in VMware Fusion 11

/ 2 minutes / macOS, BigSur, virtualization

If you find yourself needing to install an instance of macOS as a VM within VMware Fusion (which itself runs on a Mac), then you sometimes run into this issue of needing a bootable image with which to work.

There is a long history to this, but in short, macOS has had the ability to create install media buried within it for a very long time. Here are the steps to take in order to build a bootable ISO image of macOS 11.x "Big Sur".

Download macOS "Big Sur" installer to your Mac

This varies depending on which version of macOS your Mac is booting.

If you are on an older version of macOS:

  1. Check if you already have the installer in /Applications. If an older version exists there, delete it.
  2. Click Apple | System Preferences... | Software Update. You should now be able to click on [Upgrade Now] . This should download the installer /Applications/Install macOS Big Sur.app and then start it.
  3. Quit the Installer. (You don't want to run it. You just want to have it.)

If you are on macOS 11.x "Big Sur":

  1. Check if you already have the installer in /Applications. If an older version exists there, delete it.
  2. Open the App Store.
  3. Search for "Big Sur" and select "macOS Big Sur" from the list (should be first item).
  4. Click [Get] to download.

Create an ISO image

Now that you have the installer, you need to create an ISO image of the Big Sur installer. You do this using the following commands. I strongly recommend you first eject/unmount any external drives/etc. before starting. This reduces the risk of issues such as volume name collisions.

NOTE: If you have any issues, notably around the step to create the media, odds are it is due to something with regard to the volumes that the system sees. Sometimes simply quitting/restarting Terminal is enough to clear things up. Other times you may need to reboot the Mac before trying these steps again.

# Create a Big Sur Virtual Disk Image (currently at 13GB in size, and stored as /tmp/bigsur.dmg)
hdiutil create -o /tmp/bigsur -size 13G -volname bigsur -layout SPUD -fs HFS+J

# Mount this Image to macOS
hdiutil attach /tmp/bigsur.dmg -noverify -mountpoint /Volumes/bigsur

# Use macOS Big Sur Createinstallmedia Tool to create a Installer Image
sudo /Applications/Install\ macOS\ Big\ Sur.app/Contents/Resources/createinstallmedia --volume /Volumes/bigsur --nointeraction

# Unmount Volume Big Sur (note the name of the volume has changed)
sudo hdiutil eject -force /Volumes/Install\ macOS\ Big\ Sur

# Convert the bigsur.dmg to a bigsur.iso for Virtual Machine
hdiutil convert /tmp/bigsur.dmg -format UDTO -o ~/Desktop/bigsur.cdr

# Move and Rename bigsur Image to Desktop
mv ~/Desktop/bigsur.cdr ~/Desktop/bigsur.iso

Create a VM

At this point, you can build a VM:

  1. Run VMware Fusion.
  2. Create a new VM.
  3. Drag/drop the created bigsur.iso into Fusion and select macOS 10.15 (or whatever version is closest to the one you are installing).
  4. Customize the settings.
    • First set the VM name to save the file.
    • Next, specify whatever # of vCPUs and RAM you can spare for this (e.g., for starters, I typically use 4 cores and 8192 MB RAM on a Core i7 MBP I use that has 32GB RAM).
    • Verify that the CD/DVD-ROM is configured to use the .ISO image
  5. Boot the VM.
  6. Once the Installer loads, run Disk Utility.
  7. Format the VMware drive (pay careful attention to which one) using APFS and (if given the choice) GUID partitioning.
  8. Quit Disk Utility.
  9. Run macOS "Big Sur" installer as per usual.

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