Apple silicon Macs were designed to boot almost as securely from external disks as from their internal SSD. That makes macOS installation a little more complicated. Here’s how to do that.
LocalPolicy
Working with external bootable disks: how to create and add them, ownership and LocalPolicy, how that can be changed, and what happens with errors and failure.
It took over 6 months before creating bootable external disks was fairly reliable, and even then there were unexplained failures. Did someone fail to tell us something?
Two important catches that can cause a macOS installation to fail in Apple silicon: using the DFU port, and not setting up ownership correctly. Both are explained here.
Ownership can mean two very different things on Macs: it might be about Unix permissions, or Apple silicon boot policy. How to tell them apart so you use the right solution for ownership problems.
Sometimes Apple silicon Macs refuse to boot from a bootable system. How to use bputil to check LocalPolicy and work out what’s gone wrong.
How Apple silicon Macs create LocalPolicy to allow another boot volume group to be used, the problems that can occur, and how to investigate them.
To understand what might go wrong when trying to boot an Apple silicon Mac from an external disk, start with LocalPolicy: what it is, and how it works.
What are a new kernel extension and a private framework doing in macOS 11.4? Here are some details, and suggestions for further research.
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