Nix Notes

Since I started using Darwin based machines in 2003 I've used Fink, MacPorts, Stow and Homebrew.

For the last few years my go-to developer tools have been Homebrew, ASDF and Docker.

I wanted to something different to manage my development environment but with a couple of constraints:

• No need to compile packages
• Fast and reproducible

Nix had been under my radar for some time but as it had, and still has, an "incredibly steep learning curve" I was postponing the adoption.

Here are my notes about how I use it.

Install Nix

Install Nix using Determinate Nix Installer which has some good defaults

curl --proto '=https' --tlsv1.2 -sSf -L https://install.determinate.systems/nix | sh -s -- install --no-confirm

Open a new terminal and run the following command to see things are working as expected

nix-shell -p hello --run "hello"

Setting Up a Development Environment

Home Manager with Nix Flakes

I use home-manager to install packages that I need on my day to day work which are not project specific. I recommend installing it with Nix Flakes.

I don't use any advanced features like dotfiles management. I just use it to define and install packages.

Flakes

I've been migrating my shell.nix to flake.nix because it simplifies a lot version pinning. You can read more about Flakes here.

As an example this is the flake.nix I use on my Rails projects:

{
  description = "ruby 3.3 environment";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
  };

  outputs = { self, nixpkgs }:
    let
      inherit (nixpkgs.lib) genAttrs;
      supportedSystems = [ "aarch64-linux" "aarch64-darwin" ];
      forAllSystems = f: genAttrs supportedSystems (system: f system);
    in
    {
      devShells = forAllSystems (system:
        let pkgs = import nixpkgs { inherit system; };
        in {
          default = pkgs.mkShell {
            packages = with pkgs; [
              cmake
              gh
              git
              git-crypt
              gitleaks
              gnupg
              lefthook
              libyaml
              nodejs_20
              openssl
              overmind
              pkg-config
              postgresql_15
              ruby_3_3
              yarn
            ];

            shellHook = ''
              export PATH=./bin:$PATH
            '';
          };
        });
    };
}

To enable the flake you can run

nix develop

Or you can use nix-direnv to enable the console when you enter the folder.

nix-shell (deprecated)

I use a combination of nix-shell and direnv to install packages required on a particular project.

First of all install direnv

nix-channel --add https://nixos.org/channels/nixpkgs-unstable
nix-channel --update
nix-env --install --attr nixpkgs.direnv

Enable direnv on your ~/.zshrc configuration

if type direnv &>/dev/null; then
  export DIRENV_LOG_FORMAT=""
  eval "$(direnv hook zsh)"
fi

On your project add a shell.nix with your package list

with (import <nixpkgs> {});
mkShell {
  buildInputs = [
    hello
  ];
}

Create an .envrc file and allow its execution

echo "use nix" > .envrc
direnv allow

Now you can run an smoke test to execute the installed command

hello

That's it, you have hello command available on that project. Now you can install terraform, ruby ... or whatever tool you need which is specific to that project.

How do I run services?

To run services I'm using a combination of

• shell.nix to define the packages and pin versions
• direnv to start a nix-shell
• hivemind to start the processes

As an example services/redis.nix installs Hivemind and Redis and creates a Procfile which is used by Hivemind to start the processes.

nix-shell services/redis.nix

Once nix-shell is enabled, run hivemind to start the services.

Notes

nix-shell commands

Let's say you have a Rails application with a shell.nix file which defines some of its dependencies. You can run nix-shell to start a new shell with all the dependencies installed or you can run a nix-shell command to execute a command inside the new shell.

nix-shell --run "bin/rails server"

nix-shell

#!/usr/bin/env nix-shell
#!nix-shell -i bash -p restic

if [ ! -n "$RESTIC_REPOSITORY" ]; then
  echo "error: \$RESTIC_REPOSITORY not set."
  exit 1
fi

WORK_DIR=$(mktemp -d -t restic-restore-XXXXXX)

restic restore latest \
  --target $WORK_DIR \
  --include $HOME/Documents

nix develop

nix develop --command bash -c "bin/rails server"

Custom Profiles

# Create a new profile
nix-env --switch-profile /nix/var/nix/profiles/per-user/fesplugas/foo
# List installed packages
nix-env --query
# Install a new package
nix-env -iA nixpkgs.hello
# Go back to your default profile
nix-env --switch-profile $HOME/.local/state/nix/profiles/profile

Uninstall Nix?

Want to uninstall?