mirror of
https://github.com/ryan4yin/nixos-and-flakes-book
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91 lines
3.7 KiB
Markdown
91 lines
3.7 KiB
Markdown
# Downgrading or Upgrading Packages
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After using Flakes, most people are currently using the `nixos-unstable` branch of nixpkgs. However, sometimes you may encounter bugs, such as the [chrome/vscode crash problem](https://github.com/swaywm/sway/issues/7562).
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To resolve these issues, you may need to downgrade or upgrade some packages. In Flakes, all package versions and hash values correspond one-to-one to the git commit of their flake input. Therefore, to downgrade or upgrade a package, you need to lock the git commit of its flake input.
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For example, you can add multiple nixpkgs, each using a different git commit or branch:
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```nix
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{
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description = "NixOS configuration of Ryan Yin"
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inputs = {
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# default to nixos-unstable branch
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nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
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# the latest stable branch of nixpkgs, used to rollback the version of some packages
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# the current latest version is 22.11
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nixpkgs-stable.url = "github:nixos/nixpkgs/nixos-22.11";
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# we can also use git commit hash to lock the version
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nixpkgs-fd40cef8d.url = "github:nixos/nixpkgs/fd40cef8d797670e203a27a91e4b8e6decf0b90c";
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outputs = inputs@{
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self,
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nixpkgs,
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nixpkgs-stable,
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nixpkgs-fd40cef8d,
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...
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}: {
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nixosConfigurations = {
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nixos-test = nixpkgs.lib.nixosSystem rec {
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system = "x86_64-linux";
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# The core parameter, which passes the non-default nixpkgs instances to other nix modules
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specialArgs = {
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# To use packages from nixpkgs-stable, we need to configure some parameters for it first
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pkgs-stable = import nixpkgs-stable {
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system = system; # refer the `system` parameter form outer scope recursively
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# To use chrome, we need to allow the installation of non-free software
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config.allowUnfree = true;
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};
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pkgs-fd40cef8d = import nixpkgs-fd40cef8d {
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system = system;
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config.allowUnfree = true;
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};
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};
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modules = [
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./hosts/nixos-test
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# omit other configuration...
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];
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};
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};
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};
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}
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```
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And then refer to the packages from `pkgs-stable` or `pkgs-fd40cef8d` in your sub module, a home manager's sub module as an example:
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```nix
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{
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pkgs,
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config,
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# nix will search and jnject this parameter from specialArgs in flake.nix
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pkgs-stable,
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# pkgs-fd40cef8d,
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...
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}:
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{
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# refer packages from pkgs-stable instead of pkgs
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home.packages = with pkgs-stable; [
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firefox-wayland
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# chrome wayland support was broken on nixos-unstable branch, so fallback to stable branch for now
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# https://github.com/swaywm/sway/issues/7562
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google-chrome
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];
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programs.vscode = {
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enable = true;
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package = pkgs-stable.vscode; # refer vscode from pkgs-stable instead of pkgs
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};
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}
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```
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After adjusting the configuration, deploy it with `sudo nixos-rebuild switch`. This will downgrade your Firefox/Chrome/VSCode to the version corresponding to `nixpkgs-stable` or `nixpkgs-fd40cef8d`.
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According to [1000 instances of nixpkgs](https://discourse.nixos.org/t/1000-instances-of-nixpkgs/17347), it's not a good practice to use `import` in submodules to customize `nixpkgs`. Each `import` creates a new instance of nixpkgs, which increases build time and memory usage as the configuration grows. To avoid this problem, we create all nixpkgs instances in `flake.nix`.
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> according to [1000 instances of nixpkgs](https://discourse.nixos.org/t/1000-instances-of-nixpkgs/17347), it's not a good practice to use `import` in sub modules to customize `nixpkgs`, because each `import` will create a new instance of nixpkgs, which will increase the build time and memory usage as the configuration grows. So here we create all nixpkgs instances in `flake.nix` to avoid this problem.
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