nixos-anywhere

Install NixOS everywhere via ssh

README

Setting up a new machine is time-consuming, and becomes complicated when it needs to be done remotely. If you're installing NixOS, the nixos-anywhere (formerly known as nixos-remote) tool allows you to pre-configure the whole process including:

Disk partitioning and formatting
Configuring and installing NixOS
Installing additional files and software

You can then initiate an unattended installation with a single CLI command. Since nixos-anywhere can access the new machine using SSH, it's ideal for remote installations.

Once you have initiated the command, there is no need to 'babysit' the installation. It all happens automatically.

You can use the stored configuration to repeat the same installation if you need to.

Overview

If you have machines on a mix of platforms, you'll need a common installation solution that works anywhere. nixos-anywhere is ideal in this situation.

nixos-anywhere can be used equally well for cloud servers, bare metal servers such as Hetzner, and local servers accessible via a LAN. You can create standard configurations, and use the same configuration to create identical servers anywhere.

You first create Nix configurations to specify partitioning, formatting and NixOS configurations. Further options can be controlled by a flake and by run-time switches.

Once the configuration has been created, a single command will:

Connect to the remote server via SSH
Detect whether a NixOS installer is present; if not, it will use the Linux kexec tool to boot into a Nixos installer.
Use the disko tool to partition and format the hard drive
Install NixOS
Optionally install any Nix packages and other software required.
Optionally copy additional files to the new machine

It's also possible to use nixos-anywhere to simplify the installation on a machine that has no current operating system, first booting from a NixOS installer image. This feature is described in the how-to guide. It's useful because you can pre-configure your required software and preferences, and build the new machine with a single command.

Important Note: Never use a production server as the target. It will be completely overwritten and all data lost. This tool should only be used for commissioning a new computer or repurposing an old machine once all important data has been migrated.

Prerequisites

Source Machine:
- Can be any machine with Nix installed, e.g. a NixOS machine.
- Should be able to build nix derivations for the target platform. Otherwise --build-on-remote can be used.
Target Machine:
- Unless you're using the option to boot from a NixOS installer image, or providing your own kexec image, it must be running x86-64 Linux with kexec support. Most x86_64 Linux systems do have kexec support. By providing your own image you can also perform kexec for other architectures eg aarch64
- Must have at least 1.5 GB of RAM, excluding swap.

How to use nixos-anywhere

Here’s a quick summary of how to use nixos-anywhere. You can find more information in the documentation.

The tool doesn't need to be installed, since it can be run directly from this repository.

First create a repo that includes the disk configuration and a flake to configure your options. This example assumes that flakes have been enabled on your source machine.

Here’s an example of a simple disk configuration:

{ disks ? [ "/dev/vda" ], ... }:
{
  disk = {
    main = {
      type = "disk";
      device = builtins.elemAt disks 0;
      content = {
        type = "table";
        format = "gpt";
        partitions = [
          {
            name = "boot";
            start = "0";
            end = "1M";
            flags = [ "bios_grub" ];
          }
          {
            name = "ESP";
            start = "1M";
            end = "512M";
            bootable = true;
            content = {
              type = "filesystem";
              format = "vfat";
              mountpoint = "/boot";
            };
          }
          {
            name = "root";
            start = "512M";
            end = "100%";
            content = {
              type = "filesystem";
              format = "ext4";
              mountpoint = "/";
            };
          }
        ];
      };
    };
  };
}

The disko repository has several examples of disk configurations. You can adapt them to our own needs.

A simple flake may look like this:

{
  inputs.nixpkgs.url = github:NixOS/nixpkgs;
  inputs.disko.url = github:nix-community/disko;
  inputs.disko.inputs.nixpkgs.follows = "nixpkgs";
  outputs = { self, nixpkgs, disko, ... }@attrs: {
    #-----------------------------------------------------------
    # The following line names the configuration as hetzner-cloud
    # This name will be referenced when nixos-remote is run
    #-----------------------------------------------------------
    nixosConfigurations.hetzner-cloud = nixpkgs.lib.nixosSystem {
      system = "x86_64-linux";
      specialArgs = attrs;
      modules = [
        ({modulesPath, ... }: {
          imports = [
            (modulesPath + "/installer/scan/not-detected.nix")
            (modulesPath + "/profiles/qemu-guest.nix")
            disko.nixosModules.disko
          ];
          disko.devices = import ./disk-config.nix {
            lib = nixpkgs.lib;
          };
          boot.loader.grub = {
            devices = [ "/dev/sda" ];
            efiSupport = true;
            efiInstallAsRemovable = true;
          };
          services.openssh.enable = true;
          #-------------------------------------------------------
          # Change the line below replacing <insert your key here>
          # with your own ssh public key
          #-------------------------------------------------------
          users.users.root.openssh.authorizedKeys.keys = [ "<insert your key here>" ];
        })
      ];
    };
  };
}

Once you’ve created the disk configuration and the flake, you can run the tool with a single nix command, which may look like this:

nix run github:numtide/nixos-anywhere -- --flake .#hetzner-cloud [email protected]

Note that this command references the URL of your flake, in this case .#, together with the name of the system hetzner-cloud, as highlighted by the comment in the sample flake.

This will configure and build the new NixOS server. Since the configurations are defined in the flake, it will not create /etc/nixos/configuration.nix. If you need to make changes to the configuration in future, you should make the changes in the flake, and rebuild using the --flake option as shown below:

nixos-rebuild --flake <flake URL> switch

The Quickstart Guide gives more information on how to run nixos-anywhere in its simplest form. For more specific instructions to suit individual requirements, see the How To Guide.

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