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/eabc38219184cc3e04a974fe31857d8e0eac098d.tar.gz
Using latest channel, meaning all tests have passed: http://nixos.org/channels/nixos-22.11/nixexprs.tar.xz
Using latest channel, but hosted by GitHub: https://github.com/NixOS/nixpkgs/archive/nixos-22.11.tar.gz
Using latest commit for release branch, but not tested yet: https://github.com/NixOS/nixpkgs/archive/release-21.11.tar.gz

$ nix-build -I nixpkgs=http://nixos.org/channels/nixos-22.11/nixexprs.tar.xz`

$ NIX_PATH=nixpkgs=http://nixos.org/channels/nixos-22.11/nixexprs.tar.xz nix-build ...`

Using just Nix:

let
  pkgs = import (fetchTarball "https://github.com/NixOS/nixpkgs/archive/nixos-22.11.tar.gz") {};
in pkgs.stdenv.mkDerivation { ... }

To make ad-hoc environment available on NixOS:

{
  nix.nixPath = [ ("nixpkgs=" + toString pkgs.path) ];
}