M1 Macs have another hidden boot mode

However sparse Apple’s documentation might have become, when it does explain things properly, it’s amazing what’s revealed in the detail. One document every serious Mac user should read and refer to repeatedly is the Platform Security Guide, which Apple has just revised to give all the gory details of how M1 Macs start up. In the course of doing that, it reveals that these new models have a boot mode which doesn’t appear to be documented anywhere else, but which could prove a Mac-saver: Fallback Recovery OS.

If you need your M1 Mac to enter 1 True Recovery (1TR), Recovery Mode, but that fails, there’s a second copy of the software required for 1TR “for resiliency”. To boot into that, instead of just holding the Power button until 1TR starts loading, you should “double-press and hold the power button”, according to the guide.

In practice, I’ve found this requires you to press the Power button twice in rapid succession, and on the second press, instead of releasing the button, hold it pressed until recovery options are reported as loading. This works reliably on an M1 MacBook Pro, but I’ve so far been unable to get it to work at all on my M1 Mac mini, but maybe I’m just not doing it right.

What you then get is every bit as good as regular 1TR, with one significant exception: you can’t set the system security state using the Startup Security Utility. Apple explains that this is because “LLB [Low-Level Bootloader] doesn’t lock an indication into the Boot Progress Register saying it is going into recoveryOS”. But for all other purposes, this is just as good as 1TR, and is identical.

I have updated my page on M1 boot modes to include this valuable addition, which makes me even more impressed with 1TR, although maybe this fallback would be better named 2TR.