Here is how to set up Nix in single-user mode on macOS.

I have been playing with the Nix package manager lately (I will write more about it some other time). On macOS, Nix mandatorily installs itself in “multi-user mode” in macOS, which means that the build/install process is actually run under central control by a set of special build accounts. This allows concurrent users to build packages without breaking things, but for a single-user system like mine, it doesn’t add much value. Furthermore, it was inconvenient because my command-line proxy settings (i.e. the http_proxy and related environment variables) did not get properly picked up by the daemon when it changed dynamically, as it does often through the day as I move between home, office and other networks.

So, with the help of several nice people on the ##nix-darwin IRC channel, I figured out how to revert my installation to single-user Nix mode. Here it is:

Install and configure Nix as documented, or like I did, with brew cask install nix (I know—the irony of using Homebrew to install Nix!)

Next, we need to unload and stop the nix daemon:

sudo launchctl unload /Library/LaunchDaemons/org.nixos.nix-daemon.plist
sudo launchctl stop org.nixos.nix-daemon

Change the ownership of the entire /nix directory to your personal user:

chown -R yourusername /nix

Change your configuration to unset the NIX_REMOTE environment variable. This is set automatically if you use bash because the Nix installation adds it to /etc/profile, so you will have to unset it manually in your own configuration, or modify the system files (I leave that part up to you according to your setup). I use the Elvish shell, so you can use my nix.elv library, which I load from my rc.elv file like this:

# Set up Nix environment
use nix
nix:multi-user-setup
# Work without the daemon
E:NIX_REMOTE = ""

Remove the following line from /etc/nix/nix.conf:

build-users-group = nixbld

That’s it! You should now be able to run nix-env and all other Nix commands and they will operate directly, without going through the daemon.

Once you are convinced that things are working fine, and to fully cleanup the multi-user install, you can remove the Nix build group and users with these commands:

sudo dscl . -delete /Users/nixbld1
sudo dscl . -delete /Users/nixbld2
sudo dscl . -delete /Users/nixbld3
sudo dscl . -delete /Users/nixbld4
sudo dscl . -delete /Users/nixbld5
sudo dscl . -delete /Users/nixbld6
sudo dscl . -delete /Users/nixbld7
sudo dscl . -delete /Users/nixbld8
sudo dscl . -delete /Users/nixbld9
sudo dscl . -delete /Groups/nixbld

I’ll write more about my experiences with Nix in the future. Stay tuned.