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Creating Opt-In BTRFS Installation with Snapshots

Inspired from this excellent blog post.

Variables

DISK_BOOT_SIZE_MB=512
DISK_SWAP_SIZE_GB=4
DISK=/dev/vda
HOSTNAME=beef

Wipe and Partition Disk

wipefs "${DISK}" -a -f
sgdisk --zap-all "${DISK}"
sgdisk --clear \
                --new=1:0:+"${DISK_BOOT_SIZE_MB}"MiB --typecode=1:ef00 --change-name=1:EFI \
                --new=2:0:+"${DISK_SWAP_SIZE_GB}"GiB --typecode=2:8200 --change-name=2:swap \
                --new=3:0:0 --typecode=3:8300 --change-name=3:pool0_0 \
                "${DISK}"

Create Encrypted Disk

cryptsetup --verify-passphrase -v luksFormat "${DISK}"3
cryptsetup open "${DISK}"3 pool0_0
mkswap "${DISK}"2
swapon "${DISK}"2
mkfs.btrfs -f /dev/mapper/pool0_0
mkfs.vfat "${DISK}"1

Create BTRFS Subvolumes

mount -t btrfs /dev/mapper/pool0_0 /mnt
btrfs subvolume create /mnt/root
mkdir -p /mnt/home
btrfs subvolume create /mnt/home/active
btrfs subvolume create /mnt/home/snapshots
btrfs subvolume create /mnt/nix
btrfs subvolume create /mnt/persist
mkdir -p /mnt/var_local
btrfs subvolume create /mnt/var_local/active
btrfs subvolume create /mnt/var_local/snapshots
btrfs subvolume create /mnt/var_log

Take a readonly snapshot of the root subvolume, which gets rolled back to on every boot.

btrfs subvolume snapshot -r /mnt/root /mnt/root-blank

Mount Subvolumes and Partitions

umount /mnt
mount -o subvol=root,compress=zstd,noatime /dev/mapper/pool0_0 /mnt

mkdir -p /mnt/home
mount -o subvol=home/active,compress=zstd,noatime /dev/mapper/pool0_0 /mnt/home

mkdir -p /mnt/nix
mount -o subvol=nix,compress=zstd,noatime /dev/mapper/pool0_0 /mnt/nix

mkdir -p /mnt/persist
mount -o subvol=persist,compress=zstd,noatime /dev/mapper/pool0_0 /mnt/persist

mkdir -p /mnt/var/local
mount -o subvol=var_local/active,compress=zstd,noatime /dev/mapper/pool0_0 /mnt/var/local

mkdir -p /mnt/var/log
mount -o subvol=var_log,compress=zstd,noatime /dev/mapper/pool0_0 /mnt/var/log

mkdir -p /mnt/boot
mount -o defaults,nosuid,nodev,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro /dev/disk/by-partlabel/EFI /mnt/boot

Generate NixOS Hardware Configuration

nixos-generate-config --root /mnt

Force var_log subvolume to be available for boot

sed -i "/subvol=var_log/a\      neededForBoot = true;" /mnt/etc/nixos/hardware-configuration.nix

Force BTRFS mount options

Doesn'Nixos-generate config isn't seemsmart enough to beadd takingoptions theas compressionper and noaccesstime options, this is a safety net and need to review if this is just standard defaults and is not needed at a later date.here.

sed -i "s|options = \[ \(.*\) \];|options = \[ \1 \"compress=zstd\" \"noatime\"  \];|g" /mnt/etc/nixos/hardware-configuration.nix

Create Base Configuration

/etc/nixos/configuration.nix

{ config, pkgs, ... }:

{
  imports =
    [ 
      ./hardware-configuration.nix
    ];

  boot = {
    loader = {
      efi = {
        canTouchEfiVariables = false;
      };
      grub = {
        enable = true;
        device = "nodev";  # No device for EFI
        efiSupport = true;
        useOSProber = false;
        #efiInstallAsRemovableefiInstallAsRemovable = true; # in case canTouchEfiVariables doesn't work for your system
      };
    };

    supportedFilesystems = [ 
      "btrfs"
      "fat" "vfat" "exfat" "ntfs" # Microsoft 
      "cifs"                      # Windows Network Share
    ];
  };

  networking = {
    hostName = "beef"; 
    networkmanager.enable = true;
  };

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

  services = {
    cinnamon.apps.enable = false ;
    openssh = {
      enable = true;
      settings = {
        PermitRootLogin = "yes" ;
      };
    };
    xserver = { 
      enable = true;
      layout = "us";
      libinput.enable = true;

      displayManager.gdm.enable = true ;
      desktopManager.plasma5.cinnamon.enable = true;
    };
  };

  system.stateVersion = "23.05";

  time.timeZone = "America/Vancouver";

  users.users.dave = {
     isNormalUser = true;
     extraGroups = [ "wheel" ];
     packages = with pkgs; [
     ];
   };

}

Install NixOS

nixos-install

Booting into new system

Configure system

Script

#!/usr/bin/env bash
# fs-diff.sh
mkdir -p /mnt
mount -o subvol=/ /dev/mapper/pool0_0 /mnt

set -euo pipefail

OLD_TRANSID=$(sudo btrfs subvolume find-new /mnt/root-blank 9999999)
OLD_TRANSID=${OLD_TRANSID#transid marker was }

sudo btrfs subvolume find-new "/mnt/root" "$OLD_TRANSID" |
sed '$d' |
cut -f17- -d' ' |
sort |
uniq |
while read path; do
  path="/$path"
  if [ -L "$path" ]; then
    : # The path is a symbolic link, so is probably handled by NixOS already
  elif [ -d "$path" ]; then
    : # The path is a directory, ignore
  else
    echo "$path"
  fi
done

Unmount commands

umount /mnt/boot
umount /mnt/home
umount /mnt/nix
umount /mnt/persist
umount /mnt/var/local
umount /mnt/var/log
umount /mnt

Restart Install over and over

umount /boot
umount /mnt/boot
umount /mnt/home
umount /mnt/nix
umount /mnt/persist
umount /mnt/var/local
umount /mnt/var/log
umount /mnt
mkfs.btrfs -f /dev/mapper/pool0_0
mkfs.vfat /dev/vda1
mount -t btrfs /dev/mapper/pool0_0 /mnt
btrfs subvolume create /mnt/root
mkdir -p /mnt/home
btrfs subvolume create /mnt/home/active
btrfs subvolume create /mnt/home/snapshots
btrfs subvolume create /mnt/nix
btrfs subvolume create /mnt/persist
mkdir -p /mnt/var_local
btrfs subvolume create /mnt/var_local/active
btrfs subvolume create /mnt/var_local/snapshots
btrfs subvolume create /mnt/var_log
btrfs subvolume snapshot -r /mnt/root /mnt/root-blank
umount /mnt
mount -o subvol=root,compress=zstd,noatime /dev/mapper/pool0_0 /mnt
mkdir -p /mnt/home
mount -o subvol=home/active,compress=zstd,noatime /dev/mapper/pool0_0 /mnt/home
mkdir -p /mnt/nix
mount -o subvol=nix,compress=zstd,noatime /dev/mapper/pool0_0 /mnt/nix
mkdir -p /mnt/persist
mount -o subvol=persist,compress=zstd,noatime /dev/mapper/pool0_0 /mnt/persist
mkdir -p /mnt/var/local
mount -o subvol=var_local/active,compress=zstd,noatime /dev/mapper/pool0_0 /mnt/var/local
mkdir -p /mnt/var/log
mount -o subvol=var_log,compress=zstd,noatime /dev/mapper/pool0_0 /mnt/var/log
mkdir -p /mnt/boot
mount -o defaults,nosuid,nodev,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro /dev/disk/by-partlabel/EFI /mnt/boot
nixos-generate-config --root /mnt
sed -i "/subvol=var_log/a\      neededForBoot = true;" /mnt/etc/nixos/hardware-configuration.nix 
sed -i "s|options = \[ \(.*\) \];|options = \[ \1 \"compress=zstd\" \"noatime\"  \];|g" /mnt/etc/nixos/hardware-configuration.nix 
rm -rf /mnt/etc/nixos/configuration.nix
cp -R /tmp/configuration.nix /mnt/etc/nixos/
nano /mnt/etc/nixos/configuration.nix
nixos-install
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