Install NixOS with BTRFS and IN-RAM root

nixos-btrfs-tmpfs.md

Install NixOS with BTRFS and IN-RAM root

1. Format and partition the hard drive

1. Create the GPT partition table
   • $ parted /dev/sdX mklabel gpt
2. Create the UEFI FAT32 partition (which will be /dev/sdXY)
   • $ parted /dev/sdX mkpart esp fat32 1MiB 512MiB
   • $ parted /dev/sdX set 1 esp on
   • $ parted /dev/sdX set 1 boot on
   • $ mkfs.fat -F 32 -n UEFI /dev/sdXY
3. Create the SWAP partition (which will be /dev/sdXW) (optional)
   • $ parted /dev/sdX mkpart swap linux-swap 512MiB 4.5GiB
   • $ mkswap -L SWAP /dev/sdXW
4. Create the NIXOS BTRFS partition (which will be /dev/sdXZ)
   • $ parted /dev/sdX mkpart nixos btrfs 4.5GiB 100%
   • $ mkfs.btrfs -L NIXOS /dev/sdXZ

P.S. The created partitions can be viewed using $ fdisk -l /dev/sdX.

2. Setup BTRFS subvolumes

1. Mount the NIXOS partition
   • $ mount -t btrfs /dev/sdXZ /mnt
2. Create the NIX partition subvolume
   • $ btrfs subvolume create /mnt/@home
3. Create the HOME partition subvolume
   • $ btrfs subvolume create /mnt/@nix
4. Unmount the NIXOS partition
   • $ umount /mnt

3. Mount the partitions for installation

1. Mount the in-ram ROOT partition
   • $ mount -t tmpfs -o noatime,mode=755 none /mnt
2. Create persistent directories on which to mount partitions
   • $ mkdir /mnt/{boot,nix,home}
3. Mount the UEFI partition
   • $ mount -t vfat -o defaults,noatime /dev/sdXY /mnt/boot
4. Mount the NIX partition subvolume
   • $ mount -t btrfs -o noatime,compress=zstd,subvol=@nix /dev/sdXZ /mnt/nix
5. Mount the HOME partition subvolume
   • $ mount -t btrfs -o noatime,compress=zstd,subvol=@home /dev/sdXZ /mnt/home
6. Create directories that will contain persistent system files
   • $ mkdir -p /mnt/{,nix/persist/}{etc/nixos,var/log}
7. Bind system directories to their NIX persistent counterparts
   • $ mount --bind /mnt/nix/persist/etc/nixos /mnt/etc/nixos
   • $ mount --bind /mnt/nix/persist/var/log /mnt/var/log
8. Mount the SWAP partition (optional)
   • $ swapon /dev/sdXW

4. Generate NixOS configs & install

1. Let NixOS generate template configurations
   • $ nixos-generate-config --root /mnt
2. Make sure all mount points in hardware-configuration.nix are identical to the previous section
   • $ vim /mnt/etc/nixos/hardware-configuration.nix
3. Edit the configuration.nix file as needed
   • $ vim /mnt/etc/nixos/configuration.nix
     • Add machine-id file source link:
       environment.etc."machine-id".source = "/nix/persist/etc/machine-id";
     • Disable users mutability:
       users.mutableUsers = false;
     • Add user (hashed) password:
       (In another console: $ nix-shell --run 'mkpasswd -m SHA-512 -s' -p mkpasswd)
       users.users.*USERNAME*.initialHashedPassword = "*HASHED_PASSWORD*";
4. Start the installer
   • $ nixos-install --no-root-passwd
   • $ reboot

---

This file is my personal summary based on these articles:

• NixOS on Btrfs+tmpfs
• Erase your darlings
• NixOS ❄: tmpfs as root
• Paranoid NixOS Setup

good stuff

Thank you

Thank you, but I get this error:

# nixos-generate-config --root /mnt
ERROR: Not a Btrfs subvolume: Invalid argument
ERROR: Not a Btrfs subvolume: Invalid argument
writing /mnt/etc/nixos/hardware-configuration.nix...
writing /mnt/etc/nixos/configuration.nix...
For more hardware-specific settings, see https://github.com/NixOS/nixos-hardware.

Found the error, need to:

btrfs subvolume create /mnt/@

to actually create the root volume.