nix.dev/source/reference/pinning-nixpkgs.md

(ref-pinning-nixpkgs)=

Pinning Nixpkgs

Different ways:

• As environment variable: $NIX_PATH=URL
• -I command line parameter to most of commands like nix-build, nix-shell, etc
• Using builtins.fetchTarball function that fetches the channel at evaluation time

Possible URL values

• Local file path. Using just . means that nixpkgs is located in current folder.
• Pinned to a specific commit: https://github.com/NixOS/nixpkgs/archive/addcb0dddf2b7db505dae5c38fceb691c7ed85f9.tar.gz
• Using latest channel, meaning all tests have passed: http://nixos.org/channels/nixos-21.05/nixexprs.tar.xz
• Using latest channel, but hosted by github: https://github.com/NixOS/nixpkgs/archive/nixos-21.05.tar.gz
• Using latest commit for release branch, but not tested yet: https://github.com/NixOS/nixpkgs/archive/release-21.05.tar.gz

Examples

• nix-build -I ~/dev

• nix-build -I nixpkgs=http://nixos.org/channels/nixos-21.05/nixexprs.tar.xz

• NIX_PATH=nixpkgs=http://nixos.org/channels/nixos-21.05/nixexprs.tar.xz nix-build ...

• Using just Nix:

  let
    pkgs = import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/nixos-21.05.tar.gz") {};
  in pkgs.stdenv.mkDerivation { … }
  

• To make ad-hoc environment available on NixOS: nix.nixPath = [ ("nixpkgs=" + toString pkgs.path) ];