chore: vastly expand notes about nixos

snippets/nixos/commands.fish

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+#!/usr/bin/env fish
+
+nix-env -i --attr 'nixos.kubectl' 'nixos.k9s' 'nixos.helm'
+
+sudo nixos-rebuild switch

snippets/nixos/configuration.nix

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+# Basic NIX modules.
+{ config, pkgs, ... }:
+
+/* Option definitions */
+{
+  system.stateVersion = "23.11";
+
+  # Bootloader.
+  boot.loader.grub = {
+    enable = true;
+    device = "/dev/sda";
+    useOSProber = false;
+  };
+
+  # Localization.
+  console.keyMap = "us";
+  time.timeZone = "Europe/Amsterdam";
+  i18n.defaultLocale = "en_US.UTF-8";
+  i18n.extraLocaleSettings = {
+    LC_ADDRESS = "nl_NL.UTF-8";
+    LC_IDENTIFICATION = "nl_NL.UTF-8";
+    LC_MEASUREMENT = "nl_NL.UTF-8";
+    LC_MONETARY = "nl_NL.UTF-8";
+    LC_NAME = "nl_NL.UTF-8";
+    LC_NUMERIC = "nl_NL.UTF-8";
+    LC_PAPER = "nl_NL.UTF-8";
+    LC_TELEPHONE = "nl_NL.UTF-8";
+    LC_TIME = "nl_NL.UTF-8";
+  };
+
+  # Networking.
+  networking.hostName = "nixos-vm";
+
+  ## SSH.
+  # Automatically opens port 22 in the firewall.
+  services.openssh.enable = true;
+
+  # Package management.
+  nixpkgs.config.allowUnfree = true;
+  environment.systemPackages = with pkgs; [
+    git
+    tmux
+    vim
+  ];
+
+  # SUID wrappers.
+  programs.mtr.enable = true;
+  programs.gnupg.agent = {
+    enable = true;
+    enableSSHSupport = true;
+  };
+
+  # Users.
+  users.users.mike = {
+    isNormalUser = true;
+    description = "Mike Wazowski";
+    extraGroups = [
+      "networkmanager"
+      "wheel"
+    ];
+    packages = with pkgs; [
+      chezmoi
+      firefox
+      kate
+      lefthook
+      # thunderbird
+      vscode
+    ];
+  };
+
+  # Include external configuration files.
+  imports = [
+    ./hardware-configuration.nix  # usually autogenerated by the system
+    ./kde.nix
+    ./k3s.nix
+  ];
+}

snippets/nixos/k3s.nix

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+{
+  # Refer https://github.com/NixOS/nixpkgs/blob/master/pkgs/applications/networking/cluster/k3s/README.md
+  boot.kernel.sysctl."net.ipv4.ip_forward" = 1;
+  networking.firewall.enable = false;
+  services.k3s = {
+    enable = true;
+    role = "server";
+    token = "12345";
+    clusterInit = true;
+  };
+}

snippets/nixos/kde.nix

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+{
+  services.xserver = {
+    enable = true;
+    desktopManager.plasma5.enable = true;
+    xkb = {
+      layout = "it";
+      variant = "";
+    };
+  };
+  services.displayManager.sddm.enable = true;
+}