and you're just doing use flake in your .envrc?

what does your flake look like?

Yes

Right now like so

{
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
  };
  outputs = {nixpkgs, ...}: let
    system = "x86_64-linux";
    pkgs = import nixpkgs {
      inherit system;
      crossSystem = {
        config = "armv7l-linux-gnueabihf";
      };
    };
  in {
    devShells.${system}.default = import ./nix/shell.nix {inherit pkgs;};
  };
  nixConfig = {
    extraOptions = ''
      keep-outputs = true
      keep-derivations = true
    '';
  };
}

The shell.nix looks like so

{pkgs, ...}:
pkgs.mkShell {
  buildInputs = [
    pkgs.glibc
    pkgs.glibc.static
  ];

  makeFlags = [
    "CC=${pkgs.stdenv.cc.targetPrefix}cc"
    "CXX=${pkgs.stdenv.cc.targetPrefix}g++"
  ];
}

To be clear I only added the nixConfig bit today.

The rebuild happens once in a while I guess. E.g. yesterday evening I was using the dev shell (nix develop) but today in the morning gcc had to be rebuilt.

I haven't done any changes to my system or the flake in between those times

GC has this setup

    gc = {
      automatic = true;
      dates = "daily";
      options = "--delete-older-than 7d";
    };

Does this answer your questions?

Hey guys I have a question.
I was used to instantiate nixpkgs like this

pkgs = import inputs.nixpkgs {
    overlays = [
      inputs.nur.overlays.default
    ];
    system = "x86_64-linux"; # system arch (checkout hardware-configuration.nix -> nixpkgs.hostPlatform);
    config.allowUnfree = true;
  };

And then pass this configured instance as specialArgs to nixpkgs.lib.nixosSystem like this:

  nixosConfigurations.${systemSettings.hostname} = inputs.nixpkgs.lib.nixosSystem {
    modules = [ ./configuration.nix ];
    specialArgs = {
      inherit pkgs;
      inherit inputs;
      inherit systemSettings;
    };
  };

I thought that this ensures that the correctly defined nixpkgs is used throughout my configuration.nix. But now I'm getting this warning:

evaluation warning: You have set specialArgs.pkgs, which means that options like nixpkgs.config
                    and nixpkgs.overlays will be ignored. If you wish to reuse an already created
                    pkgs, which you know is configured correctly for this NixOS configuration,
                    please import the `nixosModules.readOnlyPkgs` module from the nixpkgs flake or
                    `(modulesPath + "/misc/nixpkgs/read-only.nix"), and set `{ nixpkgs.pkgs = <your pkgs>; }`.
                    This properly disables the ignored options to prevent future surprises.

Removing the inherit pkgs; line gets rid of the warning and everything stills works but now I don't understand how my modules know about the nixpkgs instance that they should be using.

I tried googling but found it really difficult to find information regarding this. Any help would be highly appreciated!
In general help for understanding how this nixpkgs.lib.nixosSystem actually works would be nice :slight_smile:

In reply to @leons_pferd:matrix.org

Hey guys I have a question.
I was used to instantiate nixpkgs like this

pkgs = import inputs.nixpkgs {
    overlays = [
      inputs.nur.overlays.default
    ];
    system = "x86_64-linux"; # system arch (checkout hardware-configuration.nix -> nixpkgs.hostPlatform);
    config.allowUnfree = true;
  };

And then pass this configured instance as specialArgs to nixpkgs.lib.nixosSystem like this:

  nixosConfigurations.${systemSettings.hostname} = inputs.nixpkgs.lib.nixosSystem {
    modules = [ ./configuration.nix ];
    specialArgs = {
      inherit pkgs;
      inherit inputs;
      inherit systemSettings;
    };
  };

I thought that this ensures that the correctly defined nixpkgs is used throughout my configuration.nix. But now I'm getting this warning:

evaluation warning: You have set specialArgs.pkgs, which means that options like nixpkgs.config
                    and nixpkgs.overlays will be ignored. If you wish to reuse an already created
                    pkgs, which you know is configured correctly for this NixOS configuration,
                    please import the `nixosModules.readOnlyPkgs` module from the nixpkgs flake or
                    `(modulesPath + "/misc/nixpkgs/read-only.nix"), and set `{ nixpkgs.pkgs = <your pkgs>; }`.
                    This properly disables the ignored options to prevent future surprises.

Removing the inherit pkgs; line gets rid of the warning and everything stills works but now I don't understand how my modules know about the nixpkgs instance that they should be using.

I tried googling but found it really difficult to find information regarding this. Any help would be highly appreciated!
In general help for understanding how this nixpkgs.lib.nixosSystem actually works would be nice :slight_smile: