lukego/hetzner-ex43-nixos.sh

## hetzner-ex43-nixos.sh
#!/usr/bin/env bash

# Installs NixOS on a Hetzner server, wiping the server.
#
# This is for a specific server configuration; adjust where needed.
#
# When the script is done, make sure to boot the server from HD, not rescue mode again.

# Explanations:
#
# * Adapted from https://gist.github.com/nh2/78d1c65e33806e7728622dbe748c2b6a
# * Following largely https://nixos.org/nixos/manual/index.html#sec-installing-from-other-distro.
# * We set a custom `configuration.nix` so that we can connect to the machine afterwards,
#   inspired by https://nixos.wiki/wiki/Install_NixOS_on_Hetzner_Online
# * This server has 2 HDDs.
#   We put everything on RAID1.
#   Storage scheme: `partitions -> RAID -> LVM -> ext4`.
# * A root user with empty password is created, so that you can just login
#   as root and press enter when using the Hetzner spider KVM.
#   Of course that empty-password login isn't exposed to the Internet.
#   Change the password afterwards to avoid anyone with physical access
#   being able to login without any authentication.


# Default options
RAIDLEVEL=1
HOSTNAME='hydra'
NETWORK_BRIDGE=0

# Default SSH key
SSH_PUBKEY="$(xargs < <(find "$HOME/.ssh" -name '*.pub' -exec cat {} \; -quit))"

# Strict mode
set -euo pipefail

echo "$@"
set -x

# Parameter parsing
while true; do
    case "$1" in
        # Construct RAID in striped mode rather than mirror
        --raid0)
            RAIDLEVEL=0
            shift
            ;;

        # Configure a network bridge and enslave the primary NIC
        --bridge)
            NETWORK_BRIDGE=1
            shift
            ;;

        # Configure a known hostname
        --hostname)
            HOSTNAME="$2"
            shift 2
            ;;

        # Provide the path to an SSH public key file to use for the root user
        --pubkey)
            SSH_PUBKEY="$(xargs < "$2")"
            shift 2
            ;;

        # Print shell statements
        --verbose|-v)
            VERBOSE=1
            shift
            ;;

        *)
            break
    esac
done

[[ -n $VERBOSE ]] && set -x

# Install dependencies
apt-get install -y sudo

# Inspect existing disks
declare -a DISKS
readarray -t DISKS < <(lsblk -Jl | jq -r '.blockdevices[] | select(.type == "disk") | .name')

# Helper function to get the correct partition name given a disk name and partition number
# partname sda 2 => /dev/sda2
# partname nvme0n1 2 => /dev/nvme0n1p2
partname() {
    if [[ $1 == nvme* ]]; then
        echo "/dev/${1}p${2}"
    else
        echo "/dev/${1}${2}"
    fi
}

# Undo existing setups to allow running the script multiple times to iterate on it.
# We allow these operations to fail for the case the script runs the first time.
set +e
umount /mnt/boot
umount /mnt
vgchange -an
set -e

# Stop all mdadm arrays that the boot may have activated.
mdadm --stop --scan

# Prevent mdadm from auto-assembling arrays.
# Otherwise, as soon as we create the partition tables below, it will try to
# re-assemple a previous RAID if any remaining RAID signatures are present,
# before we even get the chance to wipe them.
# From:
#     https://unix.stackexchange.com/questions/166688/prevent-debian-from-auto-assembling-raid-at-boot/504035#504035
# We use `>` because the file may already contain some detected RAID arrays,
# which would take precedence over our `<ignore>`.
echo 'AUTO -all
ARRAY <ignore> UUID=00000000:00000000:00000000:00000000' > /etc/mdadm/mdadm.conf

# Create partition tables (--script to not ask)
for disk in "${DISKS[@]}"; do
    parted --script "/dev/$disk" mklabel gpt
done

# Create partitions (--script to not ask)
#
# We create the 1MB BIOS boot partition at the front.
#
# Note we use "MB" instead of "MiB" because otherwise `--align optimal` has no effect;
# as per documentation https://www.gnu.org/software/parted/manual/html_node/unit.html#unit:
# > Note that as of parted-2.4, when you specify start and/or end values using IEC
# > binary units like "MiB", "GiB", "TiB", etc., parted treats those values as exact
#
# Note: When using `mkpart` on GPT, as per
#   https://www.gnu.org/software/parted/manual/html_node/mkpart.html#mkpart
# the first argument to `mkpart` is not a `part-type`, but the GPT partition name:
#   ... part-type is one of 'primary', 'extended' or 'logical', and may be specified only with 'msdos' or 'dvh' partition tables.
#   A name must be specified for a 'gpt' partition table.
# GPT partition names are limited to 36 UTF-16 chars, see https://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_entries_(LBA_2-33).
for disk in "${DISKS[@]}"; do
    parted --script --align optimal "/dev/$disk" -- \
           mklabel gpt \
           mkpart 'ESP' 1MB 2GB \
           set 1 esp on \
           mkpart 'data-partition' 3GB '100%'
done

# Relaod partitions
partprobe

for disk in "${DISKS[@]}"; do
    # Wait for all devices to exist
    udevadm settle --timeout=5 --exit-if-exists="$(partname "$disk" 1)"
    udevadm settle --timeout=5 --exit-if-exists="$(partname "$disk" 2)"

    # Wipe any previous RAID signatures
    mdadm --zero-superblock --force "$(partname "$disk" 2)"
done


# Create RAIDs
# Note that during creating and boot-time assembly, mdadm cares about the
# host name, and the existence and contents of `mdadm.conf`!
# This also affects the names appearing in /dev/md/ being different
# before and after reboot in general (but we take extra care here
# to pass explicit names, and set HOMEHOST for the rebooting system further
# down, so that the names appear the same).
# Almost all details of this are explained in
#   https://bugzilla.redhat.com/show_bug.cgi?id=606481#c14
# and the followup comments by Doug Ledford.

# An array of all partitions in the RAID
declare -a RAIDPARTS
for disk in "${DISKS[@]}"; do
    RAIDPARTS+=( "$(partname "$disk" 2)" )
done

# shellcheck disable=SC2046
mdadm --create --run --verbose /dev/md0 --level="$RAIDLEVEL" --raid-devices="${#DISKS[@]}" \
      --homehost="$HOSTNAME" --name=root0 "${RAIDPARTS[@]}"

# Assembling the RAID can result in auto-activation of previously-existing LVM
# groups, preventing the RAID block device wiping below with
# `Device or resource busy`. So disable all VGs first.
vgchange -an

# Wipe filesystem signatures that might be on the RAID from some
# possibly existing older use of the disks (RAID creation does not do that).
# See https://serverfault.com/questions/911370/why-does-mdadm-zero-superblock-preserve-file-system-information
wipefs -a /dev/md0

# Disable RAID recovery. We don't want this to slow down machine provisioning
# in the rescue mode. It can run in normal operation after reboot.
echo 0 > /proc/sys/dev/raid/speed_limit_max

# LVM
# PVs
pvcreate /dev/md0
# VGs
vgcreate vg0 /dev/md0
# LVs (--yes to automatically wipe detected file system signatures)
lvcreate --yes --extents 95%FREE -n root0 vg0  # 5% slack space

# Filesystems (-F to not ask on preexisting FS)
mkfs.ext4 -F -L root /dev/mapper/vg0-root0

for disk in "${DISKS[@]}"; do
    mkfs.fat -F 32 -n boot /dev/${disk}p1
    mkfs.fat -F 32 -n boot /dev/${disk}p1
done


# Creating file systems changes their UUIDs.
# Trigger udev so that the entries in /dev/disk/by-uuid get refreshed.
# `nixos-generate-config` depends on those being up-to-date.
# See https://github.com/NixOS/nixpkgs/issues/62444
udevadm trigger

# Wait for FS labels to appear
udevadm settle --timeout=5 --exit-if-exists=/dev/disk/by-label/root

# NixOS pre-installation mounts

# Mount target root partition
mount /dev/disk/by-label/root /mnt
modprobe vfat
modprobe nls_cp437
modprobe nls_iso8859-1
depmod
mkdir /mnt/boot
mount /dev/disk/by-label/boot /mnt/boot
mkdir /mnt/tmp

# Installing nix

# Allow installing nix as root, see
#   https://github.com/NixOS/nix/issues/936#issuecomment-475795730
mkdir -p /etc/nix
echo "build-users-group =" > /etc/nix/nix.conf

curl -L https://nixos.org/nix/install | sh
set +u +x # sourcing this may refer to unset variables that we have no control over
# shellcheck disable=SC1090
. "$HOME"/.nix-profile/etc/profile.d/nix.sh
set -u -x

# Keep in sync with `system.stateVersion` set below!
# nix-channel --add https://nixos.org/channels/nixos-20.03 nixpkgs
nix-channel --add https://nixos.org/channels/nixos-20.03 nixpkgs
nix-channel --update

# Getting NixOS installation tools
nix-env -iE "_: with import <nixpkgs/nixos> { configuration = {}; }; with config.system.build; [ nixos-generate-config nixos-install nixos-enter manual.manpages ]"

nixos-generate-config --root /mnt

# Find the name of the network interface that connects us to the Internet.
# Inspired by https://unix.stackexchange.com/questions/14961/how-to-find-out-which-interface-am-i-using-for-connecting-to-the-internet/302613#302613
RESCUE_INTERFACE=$(ip route get 8.8.8.8 | grep -Po '(?<=dev )(\S+)')

# Find what its name will be under NixOS, which uses stable interface names.
# See https://major.io/2015/08/21/understanding-systemds-predictable-network-device-names/#comment-545626
# NICs for most Hetzner servers are not onboard, which is why we use
# `ID_NET_NAME_PATH`otherwise it would be `ID_NET_NAME_ONBOARD`.
INTERFACE_DEVICE_PATH=$(udevadm info -e | grep -Po "(?<=^P: )(.*${RESCUE_INTERFACE})")
UDEVADM_PROPERTIES_FOR_INTERFACE=$(udevadm info --query=property "--path=$INTERFACE_DEVICE_PATH")

# Note: hard-code interface name because it won't match Hetzner rescue system.
NIXOS_INTERFACE=eno1

IP_V4=$(ip route get 8.8.8.8 | grep -Po '(?<=src )(\S+)')
echo "Determined IP_V4 as $IP_V4"

# Determine Internet IPv6 by checking route, and using ::1
# (because Hetzner rescue mode uses ::2 by default).
# The `ip -6 route get` output on Hetzner looks like:
#   # ip -6 route get 2001:4860:4860:0:0:0:0:8888
#   2001:4860:4860::8888 via fe80::1 dev eth0 src 2a01:4f8:151:62aa::2 metric 1024  pref medium
IP_V6="$(ip route get 2001:4860:4860:0:0:0:0:8888 | head -1 | cut -d' ' -f7 | cut -d: -f1-4)::1"
echo "Determined IP_V6 as $IP_V6"

# Determine the MAC of our primary interface so we can assign it to the bridge
read -r MAC <"/sys/class/net/$RESCUE_INTERFACE/address"
echo "Determined MAC as $MAC"

# From https://stackoverflow.com/questions/1204629/how-do-i-get-the-default-gateway-in-linux-given-the-destination/15973156#15973156
read -r _ _ DEFAULT_GATEWAY _ < <(ip route list match 0/0); echo "$DEFAULT_GATEWAY"
echo "Determined DEFAULT_GATEWAY as $DEFAULT_GATEWAY"

NET_IFACE="$NIXOS_INTERFACE"
if [[ $NETWORK_BRIDGE == "1" ]]; then
    NET_IFACE="br0"
    NET_SLAVE="bridges.br0.interfaces = [ \"$NET_IFACE\" ];"
    NET_SYSCTL='boot.kernel.sysctl = {
    "net.ipv6.conf.all.forwarding" = "1";
    "net.ipv4.ip_forward" = "1";

    # Disable netfilter for bridges, for performance and security
    # Note that this means bridge-routed frames do not go through iptables
    # https://bugzilla.redhat.com/show_bug.cgi?id=512206#c0
    "net.bridge.bridge-nf-call-ip6tables" = "0";
    "net.bridge.bridge-nf-call-iptables" = "0";
    "net.bridge.bridge-nf-call-arptables" = "0";
  };'
fi

# Generate `configuration.nix`. Note that we splice in shell variables.
cat >| /mnt/etc/nixos/configuration.nix <<EOF
{ config, pkgs, ... }:

{
  imports =
    [ # Include the results of the hardware scan.
      ./hardware-configuration.nix
    ];

  # Use GRUB2 as the boot loader.
  # We don't use systemd-boot because Hetzner uses BIOS legacy boot.
  boot.loader = {
    systemd-boot.enable = true;
    efi.canTouchEfiVariables = true;
#    devices = [ $(printf '"/dev/%s"' "${DISKS[@]}") ];
  };

  # The madm RAID was created with a certain hostname, which madm will consider
  # the "home hostname". Changing the system hostname will result in the array
  # being considered "foregin" as opposed to "local", and showing it as
  # '/dev/md/<hostname>:root0' instead of '/dev/md/root0'.

  # This is mdadm's protection against accidentally putting a RAID disk
  # into the wrong machine and corrupting data by accidental sync, see
  # https://bugzilla.redhat.com/show_bug.cgi?id=606481#c14 and onward.
  # We set the HOMEHOST manually go get the short '/dev/md' names,
  # and so that things look and are configured the same on all such
  # machines irrespective of host names.
  # We do not worry about plugging disks into the wrong machine because
  # we will never exchange disks between machines.
  environment.etc."mdadm.conf".text = ''
    HOMEHOST $HOSTNAME
  '';

  # The RAIDs are assembled in stage1, so we need to make the config
  # available there.
  boot.initrd.mdadmConf = config.environment.etc."mdadm.conf".text;

  # Network (Hetzner uses static IP assignments, and we don't use DHCP here)
  networking.useDHCP = false;

  networking.interfaces."$NET_IFACE" = {
    ipv4 = {
      addresses = [{
        # Server main IPv4 address
        address = "$IP_V4";
        prefixLength = 26;
      }];

      routes = [
        # Default IPv4 gateway route
        {
          address = "0.0.0.0";
          prefixLength = 0;
          via = "$DEFAULT_GATEWAY";
        }
      ];
    };

    ipv6 = {
      addresses = [{
        address = "$IP_V6";
        prefixLength = 64;
      }];

      # Default IPv6 route
      routes = [{
        address = "::";
        prefixLength = 0;
        via = "fe80::1";
      }];
    };
  };

  networking = {
    nameservers = [ "8.8.8.8" "8.8.4.4" ];
    hostName = "$HOSTNAME";
    ${NET_SLAVE:-}
  };

  ${NET_SYSCTL:-}

  # Initial empty root password for easy login:
  users.users.root.initialHashedPassword = "";
  services.openssh.permitRootLogin = "prohibit-password";
  services.openssh.enable = true;

  users.users.root.openssh.authorizedKeys.keys = [
    "$(echo "$SSH_PUBKEY" | xargs)"
  ];

  # This value determines the NixOS release with which your system is to be
  # compatible, in order to avoid breaking some software such as database
  # servers. You should change this only after NixOS release notes say you
  # should.
  system.stateVersion = "20.03"; # Did you read the comment?
}
EOF

# Install NixOS
NIX_PATH=nixpkgs=channel:nixpkgs-unstable
[ -d ~/.config/nix ] || mkdir -p ~/.config/nix
echo "experimental-features = nix-command" > ~/.config/nix/nix.conf
PATH="$PATH" NIX_PATH="$NIX_PATH" NIXOS_INSTALL_BOOTLOADER=1 "$(command -v nixos-install)" --no-root-passwd --root /mnt --max-jobs "$(nproc)"

umount /mnt/boot
umount /mnt

#reboot
	#!/usr/bin/env bash

	# Installs NixOS on a Hetzner server, wiping the server.
	#
	# This is for a specific server configuration; adjust where needed.
	#
	# When the script is done, make sure to boot the server from HD, not rescue mode again.

	# Explanations:
	#
	# * Adapted from https://gist.github.com/nh2/78d1c65e33806e7728622dbe748c2b6a
	# * Following largely https://nixos.org/nixos/manual/index.html#sec-installing-from-other-distro.
	# * We set a custom `configuration.nix` so that we can connect to the machine afterwards,
	# inspired by https://nixos.wiki/wiki/Install_NixOS_on_Hetzner_Online
	# * This server has 2 HDDs.
	# We put everything on RAID1.
	# Storage scheme: `partitions -> RAID -> LVM -> ext4`.
	# * A root user with empty password is created, so that you can just login
	# as root and press enter when using the Hetzner spider KVM.
	# Of course that empty-password login isn't exposed to the Internet.
	# Change the password afterwards to avoid anyone with physical access
	# being able to login without any authentication.


	# Default options
	RAIDLEVEL=1
	HOSTNAME='hydra'
	NETWORK_BRIDGE=0

	# Default SSH key
	SSH_PUBKEY="$(xargs < <(find "$HOME/.ssh" -name '*.pub' -exec cat {} \; -quit))"

	# Strict mode
	set -euo pipefail

	echo "$@"
	set -x

	# Parameter parsing
	while true; do
	case "$1" in
	# Construct RAID in striped mode rather than mirror
	--raid0)
	RAIDLEVEL=0
	shift
	;;

	# Configure a network bridge and enslave the primary NIC
	--bridge)
	NETWORK_BRIDGE=1
	shift
	;;

	# Configure a known hostname
	--hostname)
	HOSTNAME="$2"
	shift 2
	;;

	# Provide the path to an SSH public key file to use for the root user
	--pubkey)
	SSH_PUBKEY="$(xargs < "$2")"
	shift 2
	;;

	# Print shell statements
	--verbose\|-v)
	VERBOSE=1
	shift
	;;

	*)
	break
	esac
	done

	[[ -n $VERBOSE ]] && set -x

	# Install dependencies
	apt-get install -y sudo

	# Inspect existing disks
	declare -a DISKS
	readarray -t DISKS < <(lsblk -Jl \| jq -r '.blockdevices[] \| select(.type == "disk") \| .name')

	# Helper function to get the correct partition name given a disk name and partition number
	# partname sda 2 => /dev/sda2
	# partname nvme0n1 2 => /dev/nvme0n1p2
	partname() {
	if [[ $1 == nvme* ]]; then
	echo "/dev/${1}p${2}"
	else
	echo "/dev/${1}${2}"
	fi
	}

	# Undo existing setups to allow running the script multiple times to iterate on it.
	# We allow these operations to fail for the case the script runs the first time.
	set +e
	umount /mnt/boot
	umount /mnt
	vgchange -an
	set -e

	# Stop all mdadm arrays that the boot may have activated.
	mdadm --stop --scan

	# Prevent mdadm from auto-assembling arrays.
	# Otherwise, as soon as we create the partition tables below, it will try to
	# re-assemple a previous RAID if any remaining RAID signatures are present,
	# before we even get the chance to wipe them.
	# From:
	# https://unix.stackexchange.com/questions/166688/prevent-debian-from-auto-assembling-raid-at-boot/504035#504035
	# We use `>` because the file may already contain some detected RAID arrays,
	# which would take precedence over our `<ignore>`.
	echo 'AUTO -all
	ARRAY <ignore> UUID=00000000:00000000:00000000:00000000' > /etc/mdadm/mdadm.conf

	# Create partition tables (--script to not ask)
	for disk in "${DISKS[@]}"; do
	parted --script "/dev/$disk" mklabel gpt
	done

	# Create partitions (--script to not ask)
	#
	# We create the 1MB BIOS boot partition at the front.
	#
	# Note we use "MB" instead of "MiB" because otherwise `--align optimal` has no effect;
	# as per documentation https://www.gnu.org/software/parted/manual/html_node/unit.html#unit:
	# > Note that as of parted-2.4, when you specify start and/or end values using IEC
	# > binary units like "MiB", "GiB", "TiB", etc., parted treats those values as exact
	#
	# Note: When using `mkpart` on GPT, as per
	# https://www.gnu.org/software/parted/manual/html_node/mkpart.html#mkpart
	# the first argument to `mkpart` is not a `part-type`, but the GPT partition name:
	# ... part-type is one of 'primary', 'extended' or 'logical', and may be specified only with 'msdos' or 'dvh' partition tables.
	# A name must be specified for a 'gpt' partition table.
	# GPT partition names are limited to 36 UTF-16 chars, see https://en.wikipedia.org/wiki/GUID_Partition_Table#Partition_entries_(LBA_2-33).
	for disk in "${DISKS[@]}"; do
	parted --script --align optimal "/dev/$disk" -- \
	mklabel gpt \
	mkpart 'ESP' 1MB 2GB \
	set 1 esp on \
	mkpart 'data-partition' 3GB '100%'
	done

	# Relaod partitions
	partprobe

	for disk in "${DISKS[@]}"; do
	# Wait for all devices to exist
	udevadm settle --timeout=5 --exit-if-exists="$(partname "$disk" 1)"
	udevadm settle --timeout=5 --exit-if-exists="$(partname "$disk" 2)"

	# Wipe any previous RAID signatures
	mdadm --zero-superblock --force "$(partname "$disk" 2)"
	done


	# Create RAIDs
	# Note that during creating and boot-time assembly, mdadm cares about the
	# host name, and the existence and contents of `mdadm.conf`!
	# This also affects the names appearing in /dev/md/ being different
	# before and after reboot in general (but we take extra care here
	# to pass explicit names, and set HOMEHOST for the rebooting system further
	# down, so that the names appear the same).
	# Almost all details of this are explained in
	# https://bugzilla.redhat.com/show_bug.cgi?id=606481#c14
	# and the followup comments by Doug Ledford.

	# An array of all partitions in the RAID
	declare -a RAIDPARTS
	for disk in "${DISKS[@]}"; do
	RAIDPARTS+=( "$(partname "$disk" 2)" )
	done

	# shellcheck disable=SC2046
	mdadm --create --run --verbose /dev/md0 --level="$RAIDLEVEL" --raid-devices="${#DISKS[@]}" \
	--homehost="$HOSTNAME" --name=root0 "${RAIDPARTS[@]}"

	# Assembling the RAID can result in auto-activation of previously-existing LVM
	# groups, preventing the RAID block device wiping below with
	# `Device or resource busy`. So disable all VGs first.
	vgchange -an

	# Wipe filesystem signatures that might be on the RAID from some
	# possibly existing older use of the disks (RAID creation does not do that).
	# See https://serverfault.com/questions/911370/why-does-mdadm-zero-superblock-preserve-file-system-information
	wipefs -a /dev/md0

	# Disable RAID recovery. We don't want this to slow down machine provisioning
	# in the rescue mode. It can run in normal operation after reboot.
	echo 0 > /proc/sys/dev/raid/speed_limit_max

	# LVM
	# PVs
	pvcreate /dev/md0
	# VGs
	vgcreate vg0 /dev/md0
	# LVs (--yes to automatically wipe detected file system signatures)
	lvcreate --yes --extents 95%FREE -n root0 vg0 # 5% slack space

	# Filesystems (-F to not ask on preexisting FS)
	mkfs.ext4 -F -L root /dev/mapper/vg0-root0

	for disk in "${DISKS[@]}"; do
	mkfs.fat -F 32 -n boot /dev/${disk}p1
	mkfs.fat -F 32 -n boot /dev/${disk}p1
	done


	# Creating file systems changes their UUIDs.
	# Trigger udev so that the entries in /dev/disk/by-uuid get refreshed.
	# `nixos-generate-config` depends on those being up-to-date.
	# See https://github.com/NixOS/nixpkgs/issues/62444
	udevadm trigger

	# Wait for FS labels to appear
	udevadm settle --timeout=5 --exit-if-exists=/dev/disk/by-label/root

	# NixOS pre-installation mounts

	# Mount target root partition
	mount /dev/disk/by-label/root /mnt
	modprobe vfat
	modprobe nls_cp437
	modprobe nls_iso8859-1
	depmod
	mkdir /mnt/boot
	mount /dev/disk/by-label/boot /mnt/boot
	mkdir /mnt/tmp

	# Installing nix

	# Allow installing nix as root, see
	# https://github.com/NixOS/nix/issues/936#issuecomment-475795730
	mkdir -p /etc/nix
	echo "build-users-group =" > /etc/nix/nix.conf

	curl -L https://nixos.org/nix/install \| sh
	set +u +x # sourcing this may refer to unset variables that we have no control over
	# shellcheck disable=SC1090
	. "$HOME"/.nix-profile/etc/profile.d/nix.sh
	set -u -x

	# Keep in sync with `system.stateVersion` set below!
	# nix-channel --add https://nixos.org/channels/nixos-20.03 nixpkgs
	nix-channel --add https://nixos.org/channels/nixos-20.03 nixpkgs
	nix-channel --update

	# Getting NixOS installation tools
	nix-env -iE "_: with import <nixpkgs/nixos> { configuration = {}; }; with config.system.build; [ nixos-generate-config nixos-install nixos-enter manual.manpages ]"

	nixos-generate-config --root /mnt

	# Find the name of the network interface that connects us to the Internet.
	# Inspired by https://unix.stackexchange.com/questions/14961/how-to-find-out-which-interface-am-i-using-for-connecting-to-the-internet/302613#302613
	RESCUE_INTERFACE=$(ip route get 8.8.8.8 \| grep -Po '(?<=dev )(\S+)')

	# Find what its name will be under NixOS, which uses stable interface names.
	# See https://major.io/2015/08/21/understanding-systemds-predictable-network-device-names/#comment-545626
	# NICs for most Hetzner servers are not onboard, which is why we use
	# `ID_NET_NAME_PATH`otherwise it would be `ID_NET_NAME_ONBOARD`.
	INTERFACE_DEVICE_PATH=$(udevadm info -e \| grep -Po "(?<=^P: )(.*${RESCUE_INTERFACE})")
	UDEVADM_PROPERTIES_FOR_INTERFACE=$(udevadm info --query=property "--path=$INTERFACE_DEVICE_PATH")

	# Note: hard-code interface name because it won't match Hetzner rescue system.
	NIXOS_INTERFACE=eno1

	IP_V4=$(ip route get 8.8.8.8 \| grep -Po '(?<=src )(\S+)')
	echo "Determined IP_V4 as $IP_V4"

	# Determine Internet IPv6 by checking route, and using ::1
	# (because Hetzner rescue mode uses ::2 by default).
	# The `ip -6 route get` output on Hetzner looks like:
	# # ip -6 route get 2001:4860:4860:0:0:0:0:8888
	# 2001:4860:4860::8888 via fe80::1 dev eth0 src 2a01:4f8:151:62aa::2 metric 1024 pref medium
	IP_V6="$(ip route get 2001:4860:4860:0:0:0:0:8888 \| head -1 \| cut -d' ' -f7 \| cut -d: -f1-4)::1"
	echo "Determined IP_V6 as $IP_V6"

	# Determine the MAC of our primary interface so we can assign it to the bridge
	read -r MAC <"/sys/class/net/$RESCUE_INTERFACE/address"
	echo "Determined MAC as $MAC"

	# From https://stackoverflow.com/questions/1204629/how-do-i-get-the-default-gateway-in-linux-given-the-destination/15973156#15973156
	read -r _ _ DEFAULT_GATEWAY _ < <(ip route list match 0/0); echo "$DEFAULT_GATEWAY"
	echo "Determined DEFAULT_GATEWAY as $DEFAULT_GATEWAY"

	NET_IFACE="$NIXOS_INTERFACE"
	if [[ $NETWORK_BRIDGE == "1" ]]; then
	NET_IFACE="br0"
	NET_SLAVE="bridges.br0.interfaces = [ \"$NET_IFACE\" ];"
	NET_SYSCTL='boot.kernel.sysctl = {
	"net.ipv6.conf.all.forwarding" = "1";
	"net.ipv4.ip_forward" = "1";

	# Disable netfilter for bridges, for performance and security
	# Note that this means bridge-routed frames do not go through iptables
	# https://bugzilla.redhat.com/show_bug.cgi?id=512206#c0
	"net.bridge.bridge-nf-call-ip6tables" = "0";
	"net.bridge.bridge-nf-call-iptables" = "0";
	"net.bridge.bridge-nf-call-arptables" = "0";
	};'
	fi

	# Generate `configuration.nix`. Note that we splice in shell variables.
	cat >\| /mnt/etc/nixos/configuration.nix <<EOF
	{ config, pkgs, ... }:

	{
	imports =
	[ # Include the results of the hardware scan.
	./hardware-configuration.nix
	];

	# Use GRUB2 as the boot loader.
	# We don't use systemd-boot because Hetzner uses BIOS legacy boot.
	boot.loader = {
	systemd-boot.enable = true;
	efi.canTouchEfiVariables = true;
	# devices = [ $(printf '"/dev/%s"' "${DISKS[@]}") ];
	};

	# The madm RAID was created with a certain hostname, which madm will consider
	# the "home hostname". Changing the system hostname will result in the array
	# being considered "foregin" as opposed to "local", and showing it as
	# '/dev/md/<hostname>:root0' instead of '/dev/md/root0'.

	# This is mdadm's protection against accidentally putting a RAID disk
	# into the wrong machine and corrupting data by accidental sync, see
	# https://bugzilla.redhat.com/show_bug.cgi?id=606481#c14 and onward.
	# We set the HOMEHOST manually go get the short '/dev/md' names,
	# and so that things look and are configured the same on all such
	# machines irrespective of host names.
	# We do not worry about plugging disks into the wrong machine because
	# we will never exchange disks between machines.
	environment.etc."mdadm.conf".text = ''
	HOMEHOST $HOSTNAME
	'';

	# The RAIDs are assembled in stage1, so we need to make the config
	# available there.
	boot.initrd.mdadmConf = config.environment.etc."mdadm.conf".text;

	# Network (Hetzner uses static IP assignments, and we don't use DHCP here)
	networking.useDHCP = false;

	networking.interfaces."$NET_IFACE" = {
	ipv4 = {
	addresses = [{
	# Server main IPv4 address
	address = "$IP_V4";
	prefixLength = 26;
	}];

	routes = [
	# Default IPv4 gateway route
	{
	address = "0.0.0.0";
	prefixLength = 0;
	via = "$DEFAULT_GATEWAY";
	}
	];
	};

	ipv6 = {
	addresses = [{
	address = "$IP_V6";
	prefixLength = 64;
	}];

	# Default IPv6 route
	routes = [{
	address = "::";
	prefixLength = 0;
	via = "fe80::1";
	}];
	};
	};

	networking = {
	nameservers = [ "8.8.8.8" "8.8.4.4" ];
	hostName = "$HOSTNAME";
	${NET_SLAVE:-}
	};

	${NET_SYSCTL:-}

	# Initial empty root password for easy login:
	users.users.root.initialHashedPassword = "";
	services.openssh.permitRootLogin = "prohibit-password";
	services.openssh.enable = true;

	users.users.root.openssh.authorizedKeys.keys = [
	"$(echo "$SSH_PUBKEY" \| xargs)"
	];

	# This value determines the NixOS release with which your system is to be
	# compatible, in order to avoid breaking some software such as database
	# servers. You should change this only after NixOS release notes say you
	# should.
	system.stateVersion = "20.03"; # Did you read the comment?
	}
	EOF

	# Install NixOS
	NIX_PATH=nixpkgs=channel:nixpkgs-unstable
	[ -d ~/.config/nix ] \|\| mkdir -p ~/.config/nix
	echo "experimental-features = nix-command" > ~/.config/nix/nix.conf
	PATH="$PATH" NIX_PATH="$NIX_PATH" NIXOS_INSTALL_BOOTLOADER=1 "$(command -v nixos-install)" --no-root-passwd --root /mnt --max-jobs "$(nproc)"

	umount /mnt/boot
	umount /mnt

	#reboot