How do I install macOS on external drive

How do I install macOS on external drive? I want o install Big Sur on an external drive, but downloading Big Sur from Mac App Store only wants to install the OS on the internal drive. How do I get hold of a "ordinary" dmg-file?

Mac mini, macOS 12.0

Posted on Oct 4, 2021 2:40 AM

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Oct 4, 2021 3:08 AM in response to svanteh

Just pick the drive you want to install it on when it asks.

If it doesn’t offer that drive, make sure it is formatted with APFS and a GUID Partition map.

It may also need to update the firmware on the Mac. Which could be driving it to only use the internal drive—not really sure about that.


There isn’t any other installer, but perhaps it is a “stub” installer issue. You could try moving the current installer to an external drive, then run this in Terminal:

softwareupdate —-fetch-full-installer —-full-installer-version 11.6

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How do I install macOS on external drive

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