A number of Mac users that use multiple operating systems on their Mac, such as Asahi Linux users, are reporting a bug in the initial beta release of macOS 27 Golden Gate that prevents them from selecting alternate drive partitions of drives to boot from.
While this won’t affect most Mac users, those that usually boot from multiple operating systems report they are unable to do so after installing the beta, according to an AppleInsider report.
In a post to Mastodon, Asahi Linux has warned that Apple has changed how the boot picker and Startup Disk applications detect if there are valid OS boot volumes available.
PSA for #AsahiLinux users: Do NOT upgrade to macOS 27 Golden Gate!
Apple has changed how the boot picker and Startup Disk applications detect valid OS boot volumes. When using either from macOS 27, your Asahi partition will not be visible! We believe this to be a bug, and have filed a report (FB22994760).
If you have already upgraded to the beta and noticed that your Asahi partition has disappeared, do not stress. Your Asahi partition is still there, and you have not lost any data.
If you have already upgraded to macOS 27 and have a secondary installation of macOS 26 or below, set this as your default Startup Disk to restore access to Asahi. The Apple Silicon boot picker is a full-fat macOS app running in the default boot volume’s recovery environment, so its behaviour is dependent on the default boot volume’s macOS version.
If you insist on trying out macOS 27 as soon as possible, please ensure you install a secondary copy of macOS 26 first, or install macOS 27 itself on a secondary volume. We will not support users who have installed the macOS 27 beta without making contingency or rollback plans (such as ensuring at least one stable macOS version is installed).
We have patched the Asahi Installer to prevent it from running on macOS 27 until we have some idea of what’s going on. It will print a version of this message and then exit if you try to run it from the macOS 27 beta.
Asahi Linux explains that the partition still exists on Macs, and that no data has been lost. It is just a case of the partition not being detected properly.
Users who have updated to macOS 27 and have a secondary installation of macOS 26 on an external disk should set macOS 26 to be the default Startup Disk. This should restore access to the Asahi Linux partition.
AppleInsider notes that this issue also has the potential to be an issue for users with multiple partitions or disks with other versions of macOS. The publication’s testing shows that users of older macOS versions on separate partitions will encounter similar issues.
Asahi developers believe that this is caused by a bug in macOS 27, and have filed a report with Apple, number FB22994760. The developers have patched Asahi Installer to prevent it from running on macOS until a workaround can be created, or until Apple fixes a bug.
Since there are several more betas to go before the final release to the public this fall, Apple has a chance to fix things before the public release of macOS 27 Golden Gate.
Issues like this are why both Mactrast and Apple warn users not to install beta versions of macOS on their daily driver Mac. Installations of beta software should only be done on machines set aside for testing.