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NixOS

Base Image

NixOS does not publish a cloud-init enabled disk image, so you build one from the NixOS configuration in the Sherpa repository, images/nixos. It is a flake: flake.nix picks the NixOS release, flake.lock pins the exact packages, and configuration.nix sets the system up for Sherpa:

  • cloud-init, which applies Sherpa's accounts, SSH keys, hostname and management address on first boot;
  • interfaces named eth0, eth1, ..., as in the manifest;
  • passwordless sudo for the wheel group, which Sherpa's accounts join;
  • SSH password logins allowed, as on Sherpa's other Linux nodes;
  • the serial console, for sherpa console.

You can add your own packages and services to configuration.nix before building, the NixOS way of customising an image.

Build Image

With Nix installed, from a checkout of the Sherpa repository:

cd images/nixos
nix --extra-experimental-features "nix-command flakes" build \
  .#nixosConfigurations.sherpa-node.config.system.build.images.qemu
cp -L result/*.qcow2 /some/path/nixos.qcow2

Without Nix installed, build it in the official nixos/nix container. The build runs a small VM, so the container needs /dev/kvm:

cd images/nixos
docker run --rm --device /dev/kvm -v "$PWD:/src" -w /src nixos/nix sh -c '
  git config --global --add safe.directory /src
  nix --extra-experimental-features "nix-command flakes" --option sandbox false \
    --option system-features "kvm nixos-test benchmark big-parallel" \
    build .#nixosConfigurations.sherpa-node.config.system.build.images.qemu
  mkdir -p out && cp -L result/*.qcow2 out/nixos.qcow2'

The image is written to out/nixos.qcow2, owned by root. A build takes about 5 minutes. To reuse downloaded packages between builds, add -v sherpa-nix-store:/nix to keep the Nix store in a Docker volume.

To move to newer packages within the release, run nix flake update in images/nixos before building.

Import Image

sherpa server image import \
  --src /some/path/nixos.qcow2 \
  --model nixos_linux \
  --version 26.05 \
  --default

Default Node Parameters

Property Value
Tested Version 26.05
Kind Virtual Machine
CPU 2
RAM 2GB
BIOS SeaBIOS
CDROM Driver SATA
DISK virtioa.qcow2
DISK Driver virtio
ZTP Method cloud-init
Management Interface eth0
Interface Driver virtio

More memory than the other distros, because rebuilding the system with nixos-rebuild runs Nix on the node.

Example Manifest

name = "nixos-lab"
provision_current_user = true

[[nodes]]
name = "nix01"
model = "nixos_linux"

Node Access

sherpa ssh <node-name>

sherpa console <node-name>

Notes

  • Approximate time for the system to be ready: 30 seconds
  • Accounts use Bash from the system profile, /run/current-system/sw/bin/bash: NixOS has no /bin/bash. Scripts with a #!/bin/bash shebang need #!/usr/bin/env bash instead.
  • Admin rights come from the wheel group. See Personal Accounts.
  • Changes made with nixos-rebuild switch on the node keep Sherpa's accounts, because the image keeps users.mutableUsers on.