This guide walks you through installing NixOS on a Proxmox virtual machine (VM) booted from the NixOS ISO. It assumes you’re starting with a fresh virtual disk in the VM, as shown in your lsblk output. We’ll use GPT partitioning for UEFI boot, which is required for Proxmox with OVMF BIOS.

Prerequisites:

• Download the latest NixOS ISO (e.g., from nixos.org) and attach it to your Proxmox VM as a CD/DVD drive.
• In Proxmox, create a VM – for example 2GB RAM, 1 CPU core, and a 32GB SCSI disk. Initially, set BIOS to SeaBIOS (we’ll switch to OVMF later).
• Boot the VM from the ISO and log in as root (no password needed).

Step 1: Verify Disk Layout

Run this to confirm your disk is empty and the ISO is mounted:

[root@nixos:~]# lsblk
NAME  MAJ:MIN RM  SIZE RO TYPE MOUNTPOINTS
loop0   7:0    0  1.5G  1 loop /nix/.ro-store
sda     8:0    0   32G  0 disk 
sr0    11:0    1  1.6G  0 rom  /iso

Step 2: Partition the Disk (GPT for UEFI)

We’ll create:

• Partition 1: 512MiB EFI System Partition (ESP) for boot (FAT32).
• Partition 2: Remaining space for root filesystem (ext4, labeled nixos).

Use parted for GPT labeling and partitioning. Run these commands as root:

DISK=/dev/sda

sudo parted $DISK -- mklabel gpt
sudo parted $DISK -- mkpart ESP fat32 1MiB 512MiB
sudo parted $DISK -- set 1 esp on
sudo parted $DISK -- mkpart primary 512MiB 100%

Expected output (warnings are normal):

Information: You may need to update /etc/fstab.

Verify partitions:

lsblk

Now you should see:

sda      8:0    0   32G  0 disk 
├─sda1   8:1    0  511M  0 part 
└─sda2   8:2    0 31.5G  0 part 

Step 3: Format the Partitions

Format the ESP as FAT32 (label: boot) and root as ext4 (label: nixos):

sudo mkfs.fat -F 32 -n boot /dev/sda1
sudo mkfs.ext4 -L nixos /dev/sda2

Expected output:

mkfs.fat 4.2 (2021-01-31)
mkfs.fat: Warning: lowercase labels might not work properly on some systems

mke2fs 1.47.2 (1-Jan-2025)
Discarding device blocks: done                            
Creating filesystem with 8257280 4k blocks and 2064384 inodes
Filesystem UUID: 12e9e807-bdbb-4f23-89d0-5d309fd362f0
Superblock backups stored on blocks: 
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 
        4096000, 7962624

Allocating group tables: done                            
Writing inode tables: done                            
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done   

Step 4: Mount the Partitions

Mount the root filesystem and create/mount the boot partition:

sudo mount /dev/disk/by-label/nixos /mnt
sudo mkdir -p /mnt/boot
sudo mount /dev/disk/by-label/boot /mnt/boot

Verify mounts:

lsblk

You should see /mnt on sda2 and /mnt/boot on sda1.

Step 5: Generate Initial Configuration

Scan hardware and generate base config files:

sudo nixos-generate-config --root /mnt

Expected output:

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.

Step 6: Edit the Configuration (Recommended)

Edit /mnt/etc/nixos/configuration.nix to customize your setup. Use nano (or vim):

sudo nano /mnt/etc/nixos/configuration.nix

Here’s a complete example config (replace placeholders like hostname, timezone, and SSH key as needed). This enables GRUB for UEFI (removable mode for VMs), NetworkManager, a user account, SSH, and basic packages:

{ config, lib, pkgs, ... }:

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

  # Boot loader configuration for VMs without EFI variable support
  boot.loader.grub = {
    enable = true;
    device = "nodev";
    efiSupport = true;
    efiInstallAsRemovable = true;
  };
  boot.loader.efi.canTouchEfiVariables = false;  # For VMs without EFI vars (Proxmox default)

  networking.hostName = "nixos";  # Change to your preferred hostname
  networking.networkmanager.enable = true;  # Enables WiFi/Ethernet management

  # Set timezone
  time.timeZone = "Africa/Nairobi";  # Change as needed

  users.users.jkmutai = {  # Replace with your username
    isNormalUser = true;
    initialPassword = "temporarypassword";  # Change on first login!
    extraGroups = [ "wheel" "networkmanager" ]; # Enable sudo and network control
    openssh.authorizedKeys.keys = [
      "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AADBAIAsll7S1S9sqmeExwJeOJMzD5pEMvgfsYvJjxhFdHS/j"
    ];
    packages = with pkgs; [
      tree
      tmux
      htop
    ];
  };

  services.openssh = {
    enable = true;
    settings = {
      PermitRootLogin = "yes";  # For initial setup; disable later for security
      PasswordAuthentication = true;
    };
  };

  # Enable a desktop environment (optional, e.g., GNOME)
  # services.xserver.enable = true;
  # services.xserver.desktopManager.gnome.enable = true;
  # services.xserver.displayManager.gdm.enable = true;
  # environment.systemPackages = with pkgs; [ firefox ];  # Add apps

  system.stateVersion = "25.05";  # Match your NixOS version
}

Tips:

• For hashed passwords (more secure): Run mkpasswd -m sha-512 on another NixOS system, then set initialHashedPassword = "..."; instead of initialPassword.
• Print current config (excluding comments/empty lines) to verify:

  grep -v '^\s*#' /mnt/etc/nixos/configuration.nix | grep -v '^$'

Step 7: Install NixOS

Run the installer. It will build derivations, install packages, and prompt for the root password:

sudo nixos-install

Expected output (abridged):

copying channel...
building the configuration in /mnt/etc/nixos/configuration.nix...
these 252 derivations will be built:
  /nix/store/047wnsgg5rglpg2zrgsw0dwhpjly1isn-groupmems.pam.drv
  ... (many more)
...
installing the boot loader...
setting up /etc...
updating GRUB 2 menu...
installing the GRUB 2 boot loader into /boot...
Installing for x86_64-efi platform.
Installation finished. No error reported.
setting up /etc...
setting root password...
New password: 
Retype new password: 
passwd: password updated successfully
installation finished!

Step 8: Configure Proxmox for UEFI Boot

Before starting:

1. Shut down the VM in Proxmox.
2. In the Proxmox web UI:

• Select your VM > Hardware tab.
• Edit “BIOS” and change from SeaBIOS to OVMF (UEFI).
• Add an “EFI Disk” if not present (under Hardware > Add > EFI Disk, use default settings).

Step 9: Start VM and Post-Install Setup

Boot your NixOS VM from Proxmox UI or CLI

• The VM will boot into NixOS via GRUB (UEFI).
• Log in as root with the password you set.

• Change the user’s password (if using initialPassword):

  passwd cloudspinx

• Test SSH access (replace IP with your VM’s IP, e.g., from ip a):

  ssh cloudspinx@192.168.1.193

Expected SSH output:

Warning: Permanently added '192.168.1.193' (ED25519) to the list of known hosts.

[cloudspinx@nixos:~]$

Troubleshooting

• Boot failure: Ensure OVMF is set and EFI Disk is added in Proxmox. Re-run nixos-install if needed.
• No network: Enable NetworkManager in config and reboot.
• Disk labels not found: Use UUIDs from blkid in fstab or config.
• More customizations: See NixOS Manual.

Your NixOS installation is now complete! For production, disable root SSH login and use key-based auth only.