How to pin nix registry nixpkgs to release channel

cdepillabout · September 6, 2021, 5:08am

I had trouble working out how to pin the nixpkgs registry entry to a release channel. I’m posting it here in case anyone else finds it helpful.

On my system, I want the nixpkgs flake to refer to the nixos-21.05 channel (flake url: github:NixOS/nixpkgs/nixos-21.05). But I want this channel to be pinned to a known commit. I want to be able to update this manually.

In order to achieve this, I use the following steps:

Starting off, I don’t have any user registry entries:
```
$ nix registry list
....
global flake:nixpkgs github:NixOS/nixpkgs
...
```
At this point, the nixpkgs flake will refer to the master branch in github:NixOS/nixpkgs (which is currently immediately before the 21.11 release):
```
$ nix eval nixpkgs#lib.version
"21.11pre-git"
```

First, you need to add an override to make nixpkgs refer to the nixos-21.05 branch:

$ nix registry add nixpkgs github:NixOS/nixpkgs/nixos-21.05
$ nix registry list
user   flake:nixpkgs github:NixOS/nixpkgs/nixos-21.05
...    
global flake:nixpkgs github:NixOS/nixpkgs
...

You then need to pin github:NixOS/nixpkgs/nixos-21.05:

$ nix registry pin github:NixOS/nixpkgs/nixos-21.05
$ nix registry list
user   flake:nixpkgs github:NixOS/nixpkgs/nixos-21.05
user   github:NixOS/nixpkgs/nixos-21.05 github:NixOS/nixpkgs/1e5c35dfbc8e0ad8c35aa1a6446f442ca1ec5234
...
global flake:nixpkgs github:NixOS/nixpkgs
...

Now, the nixpkgs flake will refer to this known-good commit on the nixos-21.05 branch:

$ nix eval nixpkgs#lib.version
""21.05pre-git""

When you want to bump the pin to the latest version of nixos-21.05, you can use the following command:

$ nix registry pin github:NixOS/nixpkgs/nixos-21.05

Note that you must not accidentally pin the nixpkgs flake. DO NOT DO THIS:

$ nix registry pin nixpkgs
$ nix registry list
user   github:NixOS/nixpkgs/nixos-21.05 github:NixOS/nixpkgs/1e5c35dfbc8e0ad8c35aa1a6446f442ca1ec5234
user   flake:nixpkgs github:NixOS/nixpkgs/9fcf2a8a2cb0f5b78edc8ec7ca877240e7fe3009
...
global flake:nixpkgs github:NixOS/nixpkgs
...
$ nix eval nixpkgs#lib.version
"21.11pre-git"

You can see that here the nixpkgs flake is now pointing back at the master branch. It is unfortunate that Nix doesn’t just “do the right thing” here.

When you want to make the nixpkgs flake point a more recent release of NixOS (the next version will probably be 21.11), you can use the following command:

$ nix registry add nixpkgs github:NixOS/nixpkgs/nixos-21.11
$ nix registry pin github:NixOS/nixpkgs/nixos-21.11
$ nix registry list
user   github:NixOS/nixpkgs/nixos-21.05 github:NixOS/nixpkgs/1e5c35dfbc8e0ad8c35aa1a6446f442ca1ec5234
user   flake:nixpkgs github:NixOS/nixpkgs/nixos-21.11
user   github:NixOS/nixpkgs/nixos-21.11 github:NixOS/nixpkgs/068984c00e0d4e54b6684d98f6ac47c92dcb642e
...
global flake:nixpkgs github:NixOS/nixpkgs
...
$ nix eval nixpkgs#lib.version
"21.11pre-git"

(Note that this won’t actually work until the nixos-21.11 branch has been created.)

cdepillabout · October 13, 2021, 5:03am

You can also do a similar thing for other release channels / branches.

For instance, here is how to pin a flake pointing to the nixos-unstable channel:

$ nix registry add nixos-unstable github:NixOS/nixpkgs/nixos-unstable
$ nix registry list
user   flake:nixos-unstable github:NixOS/nixpkgs/nixos-unstable
...
$ nix registry pin github:NixOS/nixpkgs/nixos-unstable
$ nix registry list
user   flake:nixos-unstable github:NixOS/nixpkgs/nixos-unstable
user   github:NixOS/nixpkgs/nixos-unstable github:NixOS/nixpkgs/9bf75dd50b7b6d3ce6aaf6563db95f41438b9bdb
...

Now a command like nix shell nixos-unstable#xterm will pull xterm from nixos-unstable at commit 9bf75dd50b7b6d3ce6aaf6563db95f41438b9bdb.

bew · October 23, 2021, 7:50am

I personally don’t like the global registry, with its imperative way of management.
Instead I remove the global registry and declaratively setup the user registry.

To remove the global registry, set the flake-registry option in nix.conf to an empty registry:

github.com

bew/dotfiles/blob/99d174e92d2f6d0d50f326e875198d37b84fff28/nix/nix.conf#L6


      
          # vim:ft=conf:
          
          
# Path or URI for the global flake registry
          # => Setting it to empty needs https://github.com/NixOS/nix/issues/4874
          # => Setting it to a relative path needs https://github.com/NixOS/nix/issues/4875
          flake-registry = /home/lesell_b/.config/nix/empty-global-flake-registry.json
          # NOTE: User registry entries are stored in ~/.config/nix/registry.json, this
          #       file is managed by my home Flake.
          #       (read more in ./../nix-home/modules/nix-registry.nix)
          
          
# Enable cool stuff!
          # (NOTE: on multi-user install, the user needs to be trusted)
          experimental-features = nix-command flakes
          # NOTE: if you want to enable 'ca-references' to be able to use `nix profile install` command,
          # know that `nix-env` command will stop working, and that home-manager is ONLY compatible with
          # `nix-env` (at time ot writing).

(an empty registry looks like: { "version": 2, "flakes": [] })

To configure the user registry, it is stored in ~/.config/nix/registry.json and I configure it with a home manager module of my own:

github.com

bew/dotfiles/blob/99d174e92d2f6d0d50f326e875198d37b84fff28/nix-home/modules/nix-registry.nix

{ config, lib, pkgs, ... }:

with lib;

let
  cfg = config.nixRegistry;
in {
  options = {
    nixRegistry.indirectFlakes = mkOption {
      # NOTE: types.uniq ensures that multiple definitions of the same flake will not try to merge
      # them, it will raise an error instead.
      type = types.attrsOf (types.uniq types.attrs);
      default = {};
      description = ''
        Attrset associating a flake name to flake reference (as an attrset not as a string).
      '';
      example = {
        thepkgs = { type = "path"; path = nixpkgs.outPath; };
      };
    };

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And I use it like this:

github.com

bew/dotfiles/blob/99d174e92d2f6d0d50f326e875198d37b84fff28/flake.nix#L50-L61


      
          # Restrict user nix/registry.json to the following indirect flakes:
          nixRegistry.indirectFlakes = {
            # -> flake ref: "path:${nixpkgs.outPath}"
            pkgs = { type = "path"; path = inputs.nixpkgsStable.outPath; };
            # -> flake ref: "github:nixos/nixpkgs/nixpkgs-unstable"
            unstable = {
              type = "github";
              owner = "nixos";
              repo = "nixpkgs";
              ref = "nixpkgs-unstable";
            };
          };

To declare a pkgs flake (pinned to the nixpkgs of my home flake) and an unstable user flake (on the github’s nixpkgs-unstable branch)

Hope it helps someone

gytis-ivaskevicius · October 24, 2021, 7:35am

I autogenerate registry from flake inputs using this little module:

github.com

gytis-ivaskevicius/flake-utils-plus/blob/b4848f55c7017dadc2ff4f82296a3ca0b533e1fa/lib/options.nix

{ lib, config, inputs, ... }:

let
  inherit (lib) mkIf filterAttrs mapAttrsToList mapAttrs' mkOption types;
  mkFalseOption = description: mkOption {
    inherit description;
    default = false;
    example = true;
    type = types.bool;
  };

  flakes = filterAttrs (name: value: value ? outputs) inputs;
  flakesWithPkgs = filterAttrs (name: value: value.outputs ? legacyPackages || value.outputs ? packages) flakes;

  nixRegistry = builtins.mapAttrs
    (name: v: { flake = v; })
    flakes;
in
{
  options = {

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wmertens · February 20, 2022, 2:53pm

I think home-manager now has this as part of the nix module, see home-manager/modules/misc/nix.nix at 0232fe1b75e6d7864fd82b5c72f6646f87838fc3 · nix-community/home-manager · GitHub

delan · January 30, 2023, 4:40pm

@kouakitaki’s post makes the nixpkgs flake point to the same commit used to build the system, but it requires inputs, which in turn requires

specialArgs = { inherit inputs; } in your nixpkgs.lib.nixosSystem call
outputs = { self, nixpkgs, ... }@inputs: in your flake.nix

If your /etc/nixos only has configuration.nix and no flake.nix (like mine), you can make the nixpkgs flake point to the same commit used to build the system with

# /etc/nixos/configuration.nix
# { config, pkgs, ... }: {
  nix.registry.nixpkgs.to = { type = "path"; path = pkgs.path; };
# }

or if you’re still on NixOS 22.05 (like me)

  nix.registry.nixpkgs.to = { type = "path"; path = "${pkgs.path}"; };

This will add a system override for flake:nixpkgs pointing to your nixos channel:

$ nix registry list | grep flake:nixpkgs
system flake:nixpkgs path:/nix/store/wz4m5rihmc3wszckma7zd743bm4jaywx-nixos
global flake:nixpkgs github:NixOS/nixpkgs/nixpkgs-unstable

Now you can use nix shell nixpkgs\#foo -c (like nix run nixpkgs.foo -c before flakes) instead of nix-shell -p foo --run and get the same versions as the rest of your system!

guibou · September 6, 2023, 9:28am

I’ve done as you suggested and each call to nix run nixpkgs#xxx leads to a few second where nix copies / hash the path pkgs.path to the nix store.

Otherwise, using @koukitaki method, this does not happen.

adrian-gierakowski · April 11, 2024, 5:30pm

same issue here, any idea how to avoid this when not using a flake to build the system?