Install NixOS on Online.Net

I've tested this with the Dedibox SC2 and the Dedibox XC, but see no reason for it not to work with all of their configurations.

Start by installing a flavor of Linux (don't care which, since we'll be blowing it away) using the standard Online.net control panel. Make sure the partition layout is as you'd like it, because I'm not including instructions below for changing that.

You don't even need to wait for it to finish booting; click the rescue button on the right and tell it to boot into the ubuntu rescue console. It'll give you a temporary password for the rescue ssh session. Ssh into the rescue image and let's get started!

Preparation

Be root

No reason not to be:

sudo su
cd

Create builders

groupadd nixbld
useradd nixbld1
useradd nixbld2
useradd nixbld3
useradd nixbld4
gpasswd -a nixbld1 nixbld
gpasswd -a nixbld2 nixbld
gpasswd -a nixbld3 nixbld
gpasswd -a nixbld4 nixbld

Add missing packages

apt install bzip2 btrfs-tools

Change the UI language

All the Online.net images are set to French by default, which I don't want:

export LANG=POSIX
export LC_ALL=POSIX

Check your partitions

Now, make sure your partitions are where you expect them, on /dev/sda.

fdisk -l /dev/sda

Here's what mine look like on a Dedibox XC:

/dev/sda1 *          2048     391167    194560  83 Linux
/dev/sda2          391168 1949523967 974566400  83 Linux
/dev/sda3      1949523968 1953523711   1999872  82 Linux swap / Solaris

Format your partitions

This will blast away any existing data on your main disk, so make sure you're okay with that.

mkfs.ext2 /dev/sda1
mkfs.ext4 /dev/sda2 -L nixos

swapoff -a
mkswap /dev/sda3

Mount your freshly minted filesystems

and mount the new ones we made:

mount /dev/sda2 /mnt
mkdir /mnt/boot
mount /dev/sda1 /mnt/boot
swapon /dev/sda3

Nix-flavored stuff

Get nix onto the rescue system

We'll need some nix packages to install nix on the target:

bash <(curl https://nixos.org/nix/install)
. /root/.nix-profile/etc/profile.d/nix.sh
nix-channel --remove nixpkgs
nix-channel --add http://nixos.org/channels/nixos-17.09 nixos
nix-channel --update

cat <<EOF > configuration.nix
{ fileSystems."/" = {};
  boot.loader.grub.enable = false;
} 
EOF

export NIX_PATH=nixpkgs=/root/.nix-defexpr/channels/nixos:nixos=/root/.nix-defexpr/channels/nixos/nixos
export NIXOS_CONFIG=/root/configuration.nix
nix-env -i -A config.system.build.nixos-install -A config.system.build.nixos-option -A config.system.build.nixos-generate-config -f "<nixos>"

Make configuration for your target system

Generate a default configuration:

nixos-generate-config --root /mnt

This will generate /mnt/etc/nixos/configuration.nix and /mnt/etc/nixos/hardware-configuration.nix. Eyeball the latter (nano is preinstalled) to make sure the filesystem config looks reasonable and that it's detected your cores correctly. Then customize the former to your liking. By default it'll use DHCP, which didn't seem to work for me on online.net (please tinker and tell me if you got it working with DHCP though), so make sure to customize the network settings if you don't change anything else.

If you need to figure out your current network settings to fill in the gaps in my settings file, try cat /etc/resolv.conf and cat /etc/network/interfaces.

Here's a sample config from my box:

{ config, pkgs, ... }:

{
  imports =
    [ # Include the results of the hardware scan.
      ./hardware-configuration.nix
    ];
  
  boot.loader.grub = {
    enable  = true;
    version = 2;
    device  = "/dev/sda";
  };
  
  # Not strictly required, but useful to be able to use the serial console
  boot.kernelParams = [ "console=ttyS1" ];

  networking.hostName        = "yourhostname";
  networking.interfaces.eth0 = { ipAddress = "your ip address"; prefixLength = 24; };
  networking.defaultGateway  = "your gateway";
  networking.nameservers     = [ "62.210.16.6" "62.210.16.7" ];
 
  # By default, systemd "predictable interface names" are used for network interfaces.
  # Since the Dedibox SC only has one network interface, it is safe to disable this,
  # and simply use eth0 as above. 
  # If you remove this line, you need to replace "eth0" above by the correct interface name.
  networking.usePredictableInterfaceNames = false;

  i18n.defaultLocale = "en_US.UTF-8";

  # environment.systemPackages = with pkgs; [
  #   wget
  # ];

  time.timeZone = "America/New_York";

  services.openssh.enable = true;

  security.sudo.wheelNeedsPassword = false;

  users.extraUsers.youruser = 
    { createHome      = true;
      home            = "/home/youruser";
      description     = "your name";
      extraGroups     = [ "wheel" ];
      useDefaultShell = true;
      openssh.authorizedKeys.keys = [
        "<your pubkey here>"
      ];
    };
}

Actually install the system

unset NIXOS_CONFIG
nixos-install

That should spend some time downloading and copying stuff around, and then should fail without error. After that, tell the web console to reboot back into normal mode and your machine will be beautifully nixified. Except for the logo stuck on the Online.net console page. Let me know if you figure out how to get rid of that!

Troubleshooting

If nixos-install fails to download files from the internet, check that your rescue image's /etc/resolv.confis not a symlink. The issue should be fixed now, but at some point the nixos-install chroot process would not copy symlinks appropriately, so things would not resolve in the jail.

See this commit for the fix.