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Download OS from AppStore (eg macOS Sonoma) -- do not install
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Open terminal to get shell prompt. Go to desktop:
% cd ~/Desktop
- Create DMG container (note 1 hyphen in "-volume" and other args)
% hdiutil create -o Sonoma -size 20000m -volume Sonoma -layout SPUD -fs HFS+J
created: /Users/howes/Desktop/Sonoma.dmg
-
Mount the DMG by double-clicking it (or right-clicking and selecting DiskImageMounter)
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Copy over the installer to the DMG (note 2 hyphens in "--volume")
% sudo "/Applications/Install macOS Sonoma.app/Contents/Resources/createinstallmedia --volume /Volumes/Sonoma
Password:
Ready to start.
To continue we need to erase the volume at /Volumes/Sonoma.
If you wish to continue type (Y) then press return: y
Erasing disk: 0%... 10%... 20%... 30%... 100%
Copying essential files...
Copying the macOS RecoveryOS...
Making disk bootable...
Copying to disk: 0%... 10%... 20%... 30%... 40%... 100%
Install media now available at "/Volumes/Install macOS Sonoma"
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Eject the IMG disk (right-click and select Eject)
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Create ISO from DMG (note "UDTO" is all letters, no zero)
% hdutil convert Sonoma.dmg -format UDTO -o Sonoma
Reading Driver Descriptor Map (DDM : 0)…
Reading Apple (Apple_partition_map : 1)…
Reading (Apple_Free : 2)…
Reading disk image (Apple_HFS : 3)…
..................................................................................................................................
Elapsed Time: 19.526s
Speed: 1.0GB/s
Savings: 0.0%
created: /Users/howes/Desktop/Sonoma.cdr
- Change extension
% mv Sonoma.cdr Sonoma.iso
- Use in a VM