Reflection
Foundations · 15 minutes

Install Nix and enable flakes

Prerequisite: What Nix is and why it matters.

Outcome: nix run nixpkgs#hello prints “Hello, world!” from your shell, on any Linux, macOS, or WSL2 workstation.

Which installer

There are two installers in active use in 2026:

  • Determinate Nix Installer (recommended for this tutorial). Reliable uninstall path, enables flakes by default, works identically on Linux, macOS, and WSL2. Maintained by Determinate Systems. Source: github.com/DeterminateSystems/nix-installer.
  • Official NixOS installer. The upstream one. Works fine, but the uninstall on macOS is fragile and flakes are opt-in behind an extra config file. Source: nixos.org/download.

Both give you the same nix binary once installed. If you already run NixOS on your workstation, Nix is already there and you can skip to the “enable flakes” section below.

Install (Determinate)

$ curl --proto '=https' --tlsv1.2 -sSf -L \
    https://install.determinate.systems/nix | sh -s -- install

The installer will:

  1. ask before touching anything;
  2. create a /nix directory on the root filesystem;
  3. create a nixbld group and a set of nixbld1..nixbldN users used as build sandboxes;
  4. install a nix-daemon systemd (or launchd on macOS) service;
  5. drop a ~/.bash_profile / ~/.zshenv snippet so nix is on your PATH in future shells.

Open a new shell, then check:

$ nix --version
nix (Determinate Nix) 2.24.10

Any version >= 2.18 works for this tutorial.

Uninstall (if you ever need to): /nix/nix-installer uninstall.

Install (official upstream)

If you cannot or will not use the Determinate installer:

$ sh <(curl -L https://nixos.org/nix/install) --daemon

Then, because upstream does not enable flakes by default, create ~/.config/nix/nix.conf with:

experimental-features = nix-command flakes

The Determinate installer sets this for you.

Reference: nix.dev – installation.

Single-user vs. multi-user

You will read older docs mentioning “single-user” (Nix installed into a user’s home, no daemon) and “multi-user” (system-wide /nix, daemon-owned). Use multi-user. Both installers above give you a multi-user install by default. Single-user only exists for constrained environments; you will not hit them.

Enable flakes if not already

Flakes are still labelled “experimental” upstream but are used by every serious NixOS project today, including this one. Check:

$ cat ~/.config/nix/nix.conf 2>/dev/null | grep experimental
experimental-features = nix-command flakes

If the line is missing, add it. On multi-user installs you can also set it system-wide in /etc/nix/nix.conf; the Determinate installer puts it there.

Sanity check: run a package

$ nix run nixpkgs#hello
Hello, world!

What just happened:

  • nix run is the modern subcommand for “fetch, build if needed, and execute” a flake output.
  • nixpkgs#hello is a flake reference: the flake registered under the short name nixpkgs (there is a default registry mapping it to github:NixOS/nixpkgs), and inside it, the hello output.
  • Nix fetched Nixpkgs’ hello package into /nix/store/..., wired its PATH up, and ran hello.

Second time you run it, it is instant – the store already has it.

Try a dev shell

$ nix shell nixpkgs#jq nixpkgs#curl

You are now in a shell where jq and curl are on PATH, without touching your system installation. Exit with exit. Nothing was persisted on disk beyond the store copies.

Try running this repo’s wizard (dry run)

You do not have to actually make a fleet yet – we do that in Your first fleet. But you can prove the moving parts are wired:

$ nix run github:reflection-dev/nixops -- --help

The first invocation will download a lot (nixpkgs alone is a few hundred MB of cached artefacts). Subsequent runs are fast because they hit the store.

Common gotchas

  • error: experimental Nix feature 'nix-command' is disabled – the experimental-features line in nix.conf is missing or the file is in the wrong place. Fix and re-run.
  • error: git tree ... is dirty – you tried to build from a local path that has uncommitted changes. Flakes covers this.
  • /nix on a mounted volume is slow – that is a filesystem problem, not a Nix problem. Move /nix to a fast local disk.
  • macOS + Apple silicon + Rosetta confusion – if you see “unsupported system”, check nix config show | grep system; it should be aarch64-darwin, not x86_64-darwin. If it is wrong, reinstall on an arm64 shell.

Cachix: skip the compile

Nix can pull pre-built store paths from a binary cache, saving hours of local compilation. The public cache cache.nixos.org is enabled by default. Community caches like nix-community.cachix.org (which this repo uses for deploy-rs) speed things further; the repo’s flake.nix declares them and Nix will offer to trust them the first time.

More: nix.dev – binary caches.

What you have now

  • A working nix command on your workstation.
  • Flakes enabled.
  • A binary cache configured.
  • The vocabulary to say “I want to run flake output X” without hand- waving.

Next: the language itself. You cannot read flake.nix or hosts.nix without knowing what an attribute set is, so we do that before touching flakes.

Next: The Nix language

References for this chapter

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