2021-09-14 19:56:35 +02:00

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Tutorial: Install and configure NixOS for nix-bitcoin on a dedicated machine

This tutorial describes how to manage your Bitcoin node comfortably from your personal computer with the deployment tool krops. However, nix-bitcoin is agnostic to the deployment method and can be used with different or without such tools (see examples).

0. Preparation

Find a machine to deploy nix-bitcoin on (see hardware.md).
Optional: Make sure you have the latest firmware for your system (BIOS, microcode updates).
Optional: Disable Simultaneous Multi-Threading (SMT) in the BIOS

Researchers recommend disabling (SMT), also known as Hyper-Threading Technology in the Intel® world to significantly reduce the impact of speculative execution-based attacks (https://mdsattacks.com/).

1. NixOS installation

This is borrowed from the NixOS manual. Look there for more information.

Obtain latest NixOS. For example:

wget https://releases.nixos.org/nixos/20.09/nixos-20.09.2405.e065200fc90/nixos-minimal-20.09.2405.e065200fc90-i686-linux.iso
sha256sum nixos-minimal-20.09.2405.e065200fc90-x86_64-linux.iso
# output: 5fc182e27a71a297b041b5c287558b21bdabde7068d4fc049752dad3025df867

Alternatively you can build NixOS from source by following the instructions at https://nixos.org/nixos/manual/index.html#sec-building-cd.

Write NixOS iso to install media (USB/CD). For example:
```
cp nixos-minimal-20.09.2405.e065200fc90-x86_64-linux.iso /dev/sdX
```
Replace /dev/sdX with the correct device name. You can find this using sudo fdisk -l
Boot the system and become root
```
sudo -i
```
You will have to find out if your hardware uses UEFI or Legacy Boot for the next step. You can do that, for example, by executing
```
ls /sys/firmware/efi
```
If the file exists exists, you should continue the installation for UEFI otherwise for Legacy Boot.

Option 1: Partition and format for UEFI

parted /dev/sda -- mklabel gpt
parted /dev/sda -- mkpart primary 512MiB -8GiB
parted /dev/sda -- mkpart primary linux-swap -8GiB 100%
parted /dev/sda -- mkpart ESP fat32 1MiB 512MiB
parted /dev/sda -- set 3 boot on
mkfs.ext4 -L nixos /dev/sda1
mkswap -L swap /dev/sda2
mkfs.fat -F 32 -n boot /dev/sda3
mount /dev/disk/by-label/nixos /mnt
mkdir -p /mnt/boot
mount /dev/disk/by-label/boot /mnt/boot
swapon /dev/sda2

Option 2: Partition and format for Legacy Boot (MBR)

parted /dev/sda -- mklabel msdos
parted /dev/sda -- mkpart primary 1MiB -8GiB
parted /dev/sda -- mkpart primary linux-swap -8GiB 100%
mkfs.ext4 -L nixos /dev/sda1
mkswap -L swap /dev/sda2
mount /dev/disk/by-label/nixos /mnt
swapon /dev/sda2

Option 3: Set up encrypted partitions:

Follow the guide at https://gist.github.com/martijnvermaat/76f2e24d0239470dd71050358b4d5134.

Generate NixOS config

nixos-generate-config --root /mnt
nano /mnt/etc/nixos/configuration.nix

We now need to adjust the configuration to make sure that we can ssh into the system and that it boots correctly. We add some lines to set services.openssh such that the configuration looks as follows:

{ config, pkgs, ... }:

{
  imports = [
    ...
  ];

  # Enable the OpenSSH server.
  services.openssh = {
    enable = true;
    permitRootLogin = "yes";
  };

  # The rest of the file are default options and hints.
}

Now we open hardware-configuration.nix

nano /mnt/etc/nixos/hardware-configuration.nix

which will look similar to

{ config, pkgs, ... }:

{
  imports = [ ];

  # Add line here as explained below

  # The rest of the file are generated options.
}

Now add one of the following lines to the location mentioned in above example hardware config.

Option 1: UEFI

  boot.loader.systemd-boot.enable = true;

Option 2: Legacy Boot (MBR)

  boot.loader.grub.device = "/dev/sda";

Lastly, in rare circumstances the hardware configuration does not have a fileSystems option. In that case you need to add it with the folllowing line:

  fileSystems."/".device = "/dev/disk/by-label/nixos";

Do the installation

nixos-install

Set root password

setting root password...
Enter new UNIX password:
Retype new UNIX password:

If everything went well
```
reboot
```

2. Nix installation

The following steps are meant to be run on the machine you deploy from, not the machine you deploy to. You can also build Nix from source by following the instructions at https://nixos.org/nix/manual/#ch-installing-source.

Install Dependencies (Debian 10 Buster)

sudo apt-get install curl git gnupg2 dirmngr

Install latest Nix in "multi-user mode" with GPG Verification according to https://nixos.org/nix/download.html

curl -o install-nix-2.3.10 https://releases.nixos.org/nix/nix-2.3.10/install
curl -o install-nix-2.3.10.asc https://releases.nixos.org/nix/nix-2.3.10/install.asc
gpg2 --recv-keys B541D55301270E0BCF15CA5D8170B4726D7198DE
gpg2 --verify ./install-nix-2.3.10.asc
sh ./install-nix-2.3.10 --daemon

Then follow the instructions. Open a new terminal window when you're done.

If you get an error similar to

error: cloning builder process: Operation not permitted
error: unable to start build process
/tmp/nix-binary-tarball-unpack.hqawN4uSPr/unpack/nix-2.2.1-x86_64-linux/install: unable to install Nix into your default profile

you're likely not installing as multi-user because you forgot to pass the --daemon flag to the install script.

Optional: Disallow substitutes

You can put substitute = false to your nix.conf usually found in /etc/nix/ to build the packages from source. This eliminates an attack vector where nix's build server or binary cache is compromised.

3. Setup deployment directory

Clone this project

cd
git clone https://github.com/fort-nix/nix-bitcoin

Obtain the hash of the latest nix-bitcoin release
```
cd nix-bitcoin/examples
nix-shell
```
This will download the nix-bitcoin dependencies and might take a while without giving an output. Now in the nix-shell run
```
fetch-release > nix-bitcoin-release.nix
```

Create a new directory for your nix-bitcoin deployment and copy initial files from nix-bitcoin

cd ../../
mkdir nix-bitcoin-node
cd nix-bitcoin-node
cp -r ../nix-bitcoin/examples/{nix-bitcoin-release.nix,configuration.nix,shell.nix,krops,.gitignore} .

4. Deploy with krops

Edit your ssh config

nano ~/.ssh/config

and add the node with an entry similar to the following (make sure to fix Hostname and IdentityFile):

Host bitcoin-node
    # FIXME
    Hostname NODE_IP_ADDRESS_OR_HOST_NAME_HERE
    User root
    PubkeyAuthentication yes
    # FIXME
    IdentityFile ~/.ssh/id_...
    AddKeysToAgent yes

Make sure you are in the deployment directory and edit krops/deploy.nix
```
nano krops/deploy.nix
```
Locate the FIXME and set the target to the name of the ssh config entry created earlier, i.e. bitcoin-node.

Note that any file imported by your configuration.nix must be copied to the target machine by krops. For example, if there is an import of networking.nix you must add it to extraSources in krops/deploy.nix like this:
```
extraSources = {
    "hardware-configuration.nix".file = toString ../hardware-configuration.nix;
    "networking.nix".file = toString ../networking.nix;
};
```
Optional: Disallow substitutes

If you prefer to build the system from source instead of copying binaries from the Nix cache, add the following line to configuration.nix:
```
nix.extraOptions = "substitute = false";
```
If the build process fails for some reason when deploying with krops-deploy (see later step), it may be difficult to find the cause due to the missing output. To see the build output, SSH into the target machine and run
```
nixos-rebuild -I /var/src switch
```
Copy hardware-configuration.nix from your node to the deployment directory.
```
scp root@bitcoin-node:/etc/nixos/hardware-configuration.nix .
```
Adjust configuration by opening the configuration.nix file and enable/disable the modules you want by editing this file.
```
nano configuration.nix
```
Pay attention to lines that are preceded by FIXME comments. In particular:
1. Make sure to set your SSH pubkey. Otherwise, you loose remote access because the config does not enable permitRootLogin (unless you add that manually).
2. Uncomment the line ./hardware-configuration.nix by removing #.
Enter the deployment environment
```
nix-shell
```
Deploy with krops in nix-shell
```
deploy
```
This will now create a nix-bitcoin node on the target machine.
You can now access bitcoin-node via ssh
```
ssh operator@bitcoin-node
```
Note that you're able to log in as the unprivileged operator user because nix-bitcoin automatically authorizes the ssh key added to root.

For security reasons, all normal system management tasks can and should be performed with the operator user. Logging in as root should be done as rarely as possible.

See usage.md for usage instructions, such as how to update.

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