Note: I keep this first comment up-to-date. It includes fixes. You do not have to read the thread unless you are having trouble with its suggestions!

The macOS 15 Sequoia update takes 4 UIDs in the range we've been using, clobbering any _nixbldN users in the way (typically _nixbld1-4).

This manifests as:

• On existing installs, build errors like: error: the user '_nixbld1' in the group 'nixbld' does not exist

  To fix this, run our migration script (which relocates/replaces _nixbld users) before or after taking the macOS 15 Sequoia update:

  curl --proto '=https' --tlsv1.2 -sSf -L https://github.com/NixOS/nix/raw/master/scripts/sequoia-nixbld-user-migration.sh | bash -
  

  Caution: If you installed Nix with a third-party installer, you should check with them for additional/different instructions.

• On fresh installs (with unpatched installer versions), the following error creating user _nixbld1:

  <main> attribute status: eDSRecordAlreadyExists
  <dscl_cmd> DS Error: -14135 (eDSRecordAlreadyExists)
  

  While the 2.24.6+ installers are fixed, older installers don't all work at the moment. (The installer fixes for this have been backported for every release back to the 2.18 series.)

  If you're trying to install versions from 2.20.0 and 2.24.5, you can explicitly override the starting UID:

  NIX_FIRST_BUILD_UID="351" sh <(curl -L <whatever release-specific installer URL you need>)
  

  If you run into this error with versions older than 2.18, you'll need to download the installer tarball for your platform, unpack it, and update the first UID in install-darwin-multi-user.sh to 351.