macOS 27's boot picker stopped listing Asahi Linux partitions because Apple's boot tools started enforcing an APFS metadata flag they'd ignored for fifteen years. The Asahi installer had relied on that flag being optional since M1 landed. Suddenly, the option to boot Linux just vanished from Startup Disk and the boot picker.
How a Missing Flag Broke Boot
Asahi doesn't run inside an APFS container — it uses a small 2.5 GB APFS container holding a minimal macOS install with m1n1 as the kernel, purely to satisfy Apple's bootloader requirements. That trick worked from macOS 12 through 26. Apple even fixed bugs that only appeared when booting raw binaries instead of a real XNU kernel. Then macOS 27’s boot tooling started checking a volume metadata flag that the macOS Installer has always set, but which the boot picker previously ignored. chaos_princess dug through old macOS Installer streams and found the flag. Set it manually on an Asahi APFS container, and the boot picker respects it again.
All new Asahi installs now set that flag automatically. Existing installs can be fixed by running the Asahi installer again and selecting "Fix macOS 27 boot picker compatibility." There's also a Linux-side tool being tested — chaos_princess wrote a program to set the flag from within Linux before upgrading to macOS 27. If you're willing to risk it, clone the repo, build, run, and report back to the project's OFTC or Matrix channels.
One Byte Triggered Emergency Shutdowns
macOS 27 also pushes firmware updates to all peripherals with global firmware, including the SMC. The SMC handles battery management. Our Linux power supply driver talks to the SMC for charge state, voltage, time remaining, and health. It also uses the SMC's firmware interface to set charge thresholds. The new SMC firmware changed one battery management interface from returning a 32-bit integer to returning a single byte. Our driver saw that one-byte response and, under certain conditions, interpreted it as a battery failure — then initiated an emergency shutdown to protect the system.
Asahi patched this in the downstream kernel starting with version 7.0.12. The power supply driver now handles both firmware ABIs. No more surprise shutdowns.
Developer Betas Are Not Free
These two bugs are relatively minor. But they're a reminder that developer betas can permanently alter firmware — global firmware updates are effectively irreversible without a DFU restore. Don't install macOS 27 beta on your daily driver. The Asahi team has sacrificial machines for this. Let them burn their own hardware.
If you've already upgraded, run the installer fix before your next Linux boot. The boot picker will work again, and your battery won't kill the machine. That's a good day for a porting project that keeps chasing Apple's moving targets.
Source: Asahi Linux 7.1 Progress Report
Domain: asahilinux.org
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