Day 11 — Install NixOS lab

Updated

July 30, 2026

Day 11 — Install NixOS lab

Stage II · ~4h (hands-on heavy)
Goal: Install a disposable NixOS 26.05 “Yarara” lab system (VM strongly preferred), boot it, capture hardware config notes, and prepare for flake-based management tomorrow.

Important

Do not experiment on your only daily-driver disk. Use a VM, spare machine, or spare disk. Reinstall without drama is a feature.

Why this day exists

Generations, rollback, modules, and firewall only become real on a host. Stage I was the package manager + language. Stage II is owning a machine as code—starting with a clean install.

Theory 1 — What you are installing

Piece Role
NixOS Linux distribution built from Nix modules
nixpkgs 26.05 “Yarara” Package + module set baseline for this volume
Installer image Live environment to partition + install
First generation Initial system closure after install

After install you have a bootable system. Flake ownership is Day 12—today can use installer defaults, but mentally prepare to migrate immediately.

Theory 2 — Disposable VM emphasis

Host choice Recommendation
VM (QEMU/KVM, UTM, VirtualBox, VMware, …) Preferred
Spare laptop/NUC Good
Dual-boot daily driver Risky for learning
Cloud VM Fine if you accept networking/SSH from the start

VM resources (practical)

Resource Starting point
RAM 4–8 GB
Disk 40–64 GB+
CPU 2+ cores
Firmware UEFI if available
Snapshot Take one after first successful boot

Snapshots turn “I broke GRUB” into “restore 30 seconds.”

Theory 3 — UEFI vs legacy BIOS

Mode Common loader on NixOS
UEFI systemd-boot (often default) or GRUB EFI
BIOS/CSM GRUB

Prefer UEFI for new labs. Note which you used—Day 20 returns to boot loaders.

Theory 4 — Disk layout options

Manual (classic installer path)

  1. Partition (ESP + root, optional swap)
  2. Format
  3. Mount at /mnt, ESP at /mnt/boot
  4. nixos-generate-config --root /mnt
  5. Edit configuration.nix
  6. nixos-install

Disko (intro only)

Disko declares disks as code. Full Disko redesign is Stage VI (Day 57). Today:

  • Know Disko exists
  • Optionally follow a simple Disko example if you already know it
  • Otherwise manual once is fine and educational

Do not block install on learning Disko deeply today.

Suggested simple layout (UEFI)

ESP  (vfat)  512MB–1GB   → /boot
root (ext4 or btrfs)     → /
swap (optional)

Theory 5 — nixos-generate-config outputs

File Role
hardware-configuration.nix Detected devices, fileSystems, initrd modules
configuration.nix High-level system config (you own this)

Rules of thumb

  • Treat hardware-configuration.nix as machine-specific; rarely hand-merge casually
  • Put policy (users, services, packages) in configuration.nix / modules
  • Tomorrow both get imported from a flake

Theory 6 — Installer networking and time

Install needs:

  • Network for substitutes (unless offline media strategy)
  • Correct clock helps TLS
# live environment examples (names vary)
ip a
ping -c 2 1.1.1.1

Theory 7 — First boot mental model

After nixos-install and reboot:

bootloader → kernel+initrd → stage-1/2 → systemd → multi-user
system profile: /nix/var/nix/profiles/system
generation N is current

You can log in as root or the user you created. Prefer SSH key setup ASAP (Day 14 formalizes); avoid building habits around password-only remote root.

Theory 8 — Credentials hygiene on a lab

Practice Why
Unique lab password Compromise isolation
Note in password manager Labs still get attacked if exposed
Prefer host-only networking until ready Reduce drive-by SSH noise
Snapshot before experiments Fast recovery

Worked examples bank

Example A — Download image

Use official docs for current ISO:

Pick 26.05 graphical or minimal ISO matching your arch (x86_64, aarch64).

Verify checksums when provided.

Example B — Partition sketch (sfdisk/parted-level ideas)

/dev/vda1  EFI System  FAT32  /boot
/dev/vda2  Linux root  ext4   /

Device names: vda (virtio), sda, nvme0n1—use what the live system sees (lsblk).

Example C — Generate + install skeleton

# after mounts ready
sudo nixos-generate-config --root /mnt
sudo nano /mnt/etc/nixos/configuration.nix
sudo nixos-install
# set root password when prompted

Example D — Minimal configuration knobs to set during install

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

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

  networking.hostName = "lab";
  time.timeZone = "UTC"; # set yours

  users.users.alice = {
    isNormalUser = true;
    extraGroups = [ "wheel" ];
    # initialPassword only for offline lab convenience — rotate later
    initialPassword = "changeme";
  };

  services.openssh.enable = true; # if you want SSH into VM
  system.stateVersion = "26.05"; # match release; do not casually change later
}

Exact options must match your installer generation—adapt from generated file rather than blind paste.

Lab 1 — Plan and snapshot strategy

Write in ~/lab/90daysofx/02-nixos/day11/NOTES.md (on the host machine):

  1. Hypervisor / hardware choice
  2. UEFI or BIOS
  3. Disk size
  4. Hostname
  5. Username
  6. Networking mode (NAT/bridge)
  7. Snapshot plan

Lab 2 — Install NixOS 26.05

  1. Boot installer ISO
  2. Partition + format + mount
  3. nixos-generate-config --root /mnt
  4. Edit config: hostname, user, boot loader, optional SSH
  5. nixos-install
  6. Reboot into installed system
  7. Take a VM snapshot labeled day11-fresh-install

If install fails, journal the error class (bootloader, mount, network, disk).

Lab 3 — Post-install inventory

On the new system:

nixos-version
uname -a
lsblk -f
cat /etc/os-release
ls /etc/nixos/

Copy off-box (screenshot/scp) or retype into host NOTES.md:

  • nixos-version output
  • Disk layout
  • Boot loader in use
  • IP address if any

Lab 4 — Preserve hardware config

# on NixOS lab
sudo cp -a /etc/nixos /root/nixos-etc-backup-$(date +%F)

On host lab notes, record that Day 12 will create a flake and import hardware-configuration.nix.

Optional: already enable flakes in system config for smoother Day 12:

nix.settings.experimental-features = [ "nix-command" "flakes" ];

Then sudo nixos-rebuild switch once if you edit on the running system.

Lab 5 — Break-glass familiarity

Without destroying the snapshot casually:

  1. Locate boot menu / how to pick previous generation (may only have gen 1)
  2. Confirm you can log in on console
  3. If SSH enabled, log in from host once

Common gotchas

Symptom Theory
No bootable device ESP not mounted at /mnt/boot or wrong firmware mode
Install can’t reach cache Network/DNS in live env
Forgot root password Live ISO recovery / reinstall—why snapshots matter
hardware-configuration wrong root UUID Generated before final mounts
Using unstable ISO by mistake Check 26.05 label
Daily driver install “for fun” Restore from backup; prefer VM next time

Checkpoint

  • Disposable NixOS 26.05 lab boots
  • User + privilege path known (root/wheel)
  • Disk + boot mode documented
  • /etc/nixos inspected
  • VM snapshot taken (if VM)
  • Notes stored on host machine

Commit

# on host workstation notes repo
cd ~/lab/90daysofx/02-nixos/day11
git init 2>/dev/null || true
git add .
git commit -m "day11: nixos 26.05 lab install notes"

Tomorrow

Day 12 — Flake host skeleton. Put the machine under nixosConfigurations and rebuild with nixos-rebuild switch --flake .#host—flakes from the first serious ownership moment.