We’ve finally bikeshedded final values for the new macOS UID/GID values to handle the Sequoia issues; an Apple devrel suggested the range above 350 and we have refined that to 351+ (i.e. _nixbld1 having UID 351, etc.) to avoid an off‐by‐one compared to the previous UIDs and the Linux UIDs, and to maintain the correspondence between the last digit of the build user names and the last digit of their UIDs.

We are also switching new installs to use GID 350, to align with the new UIDs (without overlapping them, as before and on Linux), because using a GID in the system range avoids the Nix build users group cluttering up System Settings.

Hopefully you can align with upstream Nix on this so that we can all be on the same page and finally put this issue behind us! (Except, uh, every installation is still going to break on upgrade. I don’t suppose you’re in a better position than upstream to make an automatic migration happen? We have a script, but informing people they need to run it is another thing…)

See also: NixOS/nix#10919 (comment), NixOS/nix#11372, abathur/nix#15.