Extract ISO Image from a macOS installer

Step 1

Download macOS Installer (InstallAssistant.pkg). Here is the link to Sonoma beta installer:

Step 2

Run InstallAssistant.pkg by double-clicking on it. This will move Install macOS Sonoma beta.app to /Applications folder.

Step 3

Create a new DMG file, open Terminal and run:

hdiutil create -o /tmp/Somona -size 16000m -volname Somona -layout SPUD -fs HFS+J

The above command will create a 16GB DMG file called Somona in /tmp folder

Step 4

Mount the DMG file we just created:

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

Step 5

Use createinstallmedia to create the macOS installer on the mounted volume:

sudo /Applications/Install\ macOS\ Sonoma\ beta.app/Contents/Resources/createinstallmedia --volume /Volumes/Somona

Step 6

Unmount the volume we've just created:

sudo hdiutil detach /Volumes/Install\ macOS\ Sonoma\ beta

Step 8

Convert the DMG disk image file to an ISO disk image file (technically a CDR file):

sudo hdiutil convert /tmp/Somona.dmg -format UDTO -o ~/tmp/Somona.cdr

Step 9

Finally rename the CDR file to ISO:

sudo mv ~/tmp/Somona.cdr ~/tmp/Somona.iso

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