Reinstall NixOS -- with flakes and home manager

1

I want to reinstall and recreate my system. I have /home files backed up.
The system uses flakes and home manager, and the config files are stored in /home.
Unstable branch.

If I just run the automated installer, boot into the new system, copy over my config file, and rebuild, I will get errors about home manager not being installed etc.
(I know because I tried…)
So what’s the best (or most painless) strategy to get going?

2

Not the most experienced NixOS user here but I’ve installed NixOS on my machine several times and also have helped move my friends over to NixOS.

TL;DR: I install NixOS with the bare minimum config I need and once I’ve booted into the persistent system, I apply the config I want. It’s safer this way for me since I can always just rollback.

Here’s the approach I follow now:

PS: I don’t use the graphical installer; so my steps may get a little technical.

  • Once on the bootable media, I launch gparted and partition the way my friends want. A simple scheme I go for is a 1024 MiB fat32 boot partition and the remaining to be the actual usable space.
  • Second, I mount the “remaining” partition to /mnt and then the boot partition to /mnt/boot.
  • Third, I run sudo nixos-generate-config --root /mnt which creates two files (config and hardware config)
  • Now, I edit these files to configure some basic things like:
    • Creating a user
    • Setting a hostname
    • Making sure I install a browser and a text editor
  • Once done and saved, I run sudo nixos-install --root /mnt and then wait.
  • Reboot into your new system.

Doing it this way means I have to apply my personal config later but it gives me that 1st persistent generation to fallback on since otherwise I’d have to redo the entire thing all over.

2 Likes
3

This is where my troubles begin. When applying my config, it complains that home manager is missing, and other errors.

4

In that case, please share a link to your config, if public, otherwise the relevant bits of it; and of course, the error(s) you get.

5

Are you using the home-manager nixos module in your flake’s systemConfiguration? When you change your home-manager configuration do you use nixos-rebuild or home-manager switch?

https://nix-community.github.io/home-manager/index.xhtml#sec-flakes-nixos-module

6

Yes, home-manager is in the flake, as below.
I do nixos-rebuild switch --flake ~/nixos#nixos

{
    inputs = {
    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
    home-manager.url = "github:nix-community/home-manager";
    home-manager.inputs.nixpkgs.follows = "nixpkgs";
    nix-snapd.url = "github:io12/nix-snapd";
    nix-snapd.inputs.nixpkgs.follows = "nixpkgs";
  };

  outputs = { self, nixpkgs, home-manager, nix-snapd }: {

    nixosConfigurations.nixos = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      modules = [
      ./configuration.nix
      home-manager.nixosModules.home-manager
      nix-snapd.nixosModules.default

      {
    home-manager.useGlobalPkgs = true;
    home-manager.useUserPackages = true;
    home-manager.users.shmuel = import ./home.nix;
    services.snap.enable = true;
  }
      ];

    };
  };
}
7

Unsure what nix-snapd is, but shouldn’t that home manager config be within home-manager.nixosModules.home-manager instead of nix-snapd.nixosModules.default?

8

Maybe the problem would be solved by running this before rebuild?

sudo nix-channel --add https://github.com/nix-community/home-manager/archive/master.tar.gz home-manager

sudo nix-channel --update
9

That looks correct to me.

When I install on a new computer I haven’t used yet I usually start with the base configuration from the live image and integrate the hardware modifications into my flake.

If I’m reinstalling I partition the disk, mount the necessary partitions in /mnt and run nix-shell -p git sudo nixos-install --flake "https://url-to-my-flake#system-name directly from the live CD. The nix-shell -p git part is because IIRC git is not installed by default on the live image and I cannot install some flake deps without it. I documented this in my flake’s readme: steinuil/flakes - flakes - mani mani

If you have a spare system with Nix installed, you can try cding into your flake directory, run nix repl, then :lf . and then :b nixosConfigurations.your-system.build.toplevel to see if your system configuration builds correctly outside of the live CD.

Nope, those config options go into the nixos configuration, so they’re fine there!

2 Likes