### Build NixOS ISO from NixOS in one line :

nix-build '<nixpkgs/nixos>' -A config.system.build.isoImage -I nixos-config=iso.nix

-A is the action, we're telling it to build the iso
-I is the configuration file for it (capital eye -> I)

### Virtual Box NixOS iso :

nixos-gnome-23.05.2084.08700de174b-x86_64-linux
200GB of Storage
6000MB of RAM

[ganitak@nixos:/]$ lsblk
NAME MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
sda    8:0    0   150G  0 disk
├─sda1
│      8:1    0   512M  0 part /boot
├─sda2
│      8:2    0 140.7G  0 part /nix/store
│                              /
└─sda3
       8:3    0   8.8G  0 part [SWAP]
sr0   11:0    1   2.3G  0 rom  /run/media/ganitak/nixos-gnome-23.05-x86_64

[ganitak@nixos:/]$ nix-shell -p
[ganitak@nixos:/]$ nix-shell -p

[nix-shell:/]$ ll
total 56
drwxr-xr-x   2 root root  4096 Jul 30 19:36 bin
drwxr-xr-x   4 root root  4096 Jan  1  1970 boot
drwxr-xr-x  19 root root  3380 Jul 30 19:51 dev
drwxr-xr-x  28 root root  4096 Jul 30 19:36 etc
drwxr-xr-x   3 root root  4096 Jul 30 19:12 home
drwx------   2 root root 16384 Jul 30 18:34 lost+found
drwxr-xr-x   4 root root  4096 Jul 30 18:36 nix
dr-xr-xr-x 205 root root     0 Jul 30 19:36 proc
drwx------   4 root root  4096 Jul 30 19:37 root
drwxr-xr-x  24 root root   620 Jul 30 19:51 run
drwxr-xr-x   2 root root  4096 Jul 30 19:12 srv
dr-xr-xr-x  13 root root     0 Jul 30 19:36 sys
drwxrwxrwt  12 root root  4096 Jul 30 20:09 tmp
drwxr-xr-x   3 root root  4096 Jul 30 19:12 usr
drwxr-xr-x   9 root root  4096 Jul 30 19:36 var

Flatpak has been mainly driven by Alex Larsson, with some help from Matthias Clasen, David King, and others.
https://www.socallinuxexpo.org/sites/default/files/presentations/Flatpak-Scale-15x.pdf 2017

### Linux
systemd is the “init” process of the system (i.e. PID 1)

**To reboot the system, run**

$ reboot

which is equivalent to systemctl reboot.
Alternatively, you can quickly reboot the system using **kexec**
- which bypasses the BIOS by directly loading the new kernel into memory:
Alternitively you can use **systemctl kexec**

### Control Groups

To keep track of the processes in a running system, systemd uses control groups (**cgroups**).
A control group is a set of processes
- **used to allocate resources** such as **CPU, memory** or **I/O bandwidth**.
There can be multiple control group hierarchies, allowing each kind of resource to be managed independently.

The command **systemd-cgls** lists all control groups in the systemd hierarchy, which is what systemd uses to keep track of the processes belonging to each service or user session:

$ systemd-cgls

Install Home Manager in
/etc/nixos/configuration.nix

nixpkgs.config.packageOverrides = pkgs: {
  home-manager = pkgs.home-manager.override {
    enable = true;
  };
};

#### Update your Nix package definitions by running the following command:

sudo nix-channel --update

Install Vim using the Nix package manager with the following command:

nix-env -iA nixpkgs.vim

error: attribute 'nixpkgs' in selection path 'nixpkgs.vim' not found

To use Nixpkgs repositories effectively on NixOS, you mainly need a good understanding of Nix and NixOS concepts. Here are the prerequisites:

Nix Package Manager: Ensure you have Nix installed on your NixOS system. Nix is the package manager used to manage and install packages from Nixpkgs.

To install Nix on NixOS, it typically comes pre-installed. However, if you need to install it manually, you can run:

bash

sudo nix-channel --add https://nixos.org/channels/nixos-unstable nixos
sudo nix-channel --update

Note: You may choose a different channel, depending on your stability preferences.

Understanding Nix Concepts: Familiarize yourself with the core concepts of Nix, such as derivations, store paths, expressions, and how the Nix store works. Understanding these concepts will help you work with Nixpkgs and write Nix expressions more effectively.

Nixpkgs Repository: The Nixpkgs repository contains a vast collection of packages and configuration files for NixOS. On NixOS, the Nixpkgs repository is typically located at /nix/var/nix/profiles/per-user/root/channels/nixos.

Nix Channels: NixOS has the nixos channel enabled by default, which provides the stable version of Nixpkgs. You can also enable other channels (e.g., nixpkgs-unstable for more recent packages) by modifying your /etc/nixos/configuration.nix file. Channels are used to access predefined sets of packages maintained by the Nix community.

NixOS Configuration: On NixOS, you manage system configurations using the /etc/nixos/configuration.nix file. It is essential to have a basic understanding of NixOS configuration options and how to modify them to customize your system.

NixOS Command-Line Tools: Familiarize yourself with NixOS command-line tools like nixos-rebuild, which is used to build and switch system configurations.

By having these prerequisites in place, you can effectively use Nixpkgs repositories on NixOS to manage packages and configurations on your system. You can refer to the official Nix documentation and NixOS documentation for more detailed information and guides on how to use Nix and Nixpkgs effectively on NixOS.