Failing to upgrade Nix on macOS

[noghartt]

Trying to upgrade my Nix binary to the new release (v2.25.4), but having this error:

> sudo -i nix upgrade-nix -vvv
found Nix in '/run/current-system/sw/bin'
error: Nix on NixOS must be upgraded via 'nixos-rebuild'

I'm running Nix on a macOS with nix-darwin. My current version is:

> nix --version
nix (Nix) 2.24.10

[cole-h]

This is likely because you're using nix-darwin (which mimicked NixOS's setup of using /run/current-system).

You should probably prefer to upgrade in whatever way they prefer (maybe their docs has a hint / instructions on this), but (not recommended and not tested) you may also be able to get around it if you specify a profile with nix upgrade-nix --profile ....