Overview of the NixOS Linux distribution

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NixOS is a Linux distribution based on the Nix Package Manager. It supports reproducible and declarative system-wide configuration management as well as atomic upgrades and rollbacks. Alongside this declarative operation mode, NixOS supports imperative package and user management. In NixOS, all components of the distribution - including the kernel, system packages and configuration files - are built by Nix from purely functional Nix Expressions. Since Nix supports binary caching, this provides a convenient compromise between source-based and binary approaches, allowing the use of a binaries for standard components while allowing the user to customize packages and modules when needed. Stable NixOS releases are delivered biannually, with the latest stable version being 17.03. NixOS was created by Eelco Dolstra and Armijn Hemel, and initially released in 2003. It is community developed and maintained under the stewardship of the NixOS Foundation.

Usage

Declarative Configuration

One of NixOS's most distinguishing features is the ability to declaratively configure the whole system. This is done by specifying a configuration file which defines which packages are installed on the system, which services to run and various other settings and options. This file is normally called configuration.nix and is found by default at /etc/nixos, although another location can be set using the environment variable NIX_PATH. The system configuration is then built with the command nixos-rebuild. The following is an example of a configuration.nix file:

{ config, pkgs, ... }: 

{
    # Import other configuration modules
    # (hardware-configuration.nix is autogenerated upon installation)
    # paths in nix expressions are always relative the file which defines them
    imports =
        [
            ./hardware-configuration.nix
            ./my-dev-tools.nix
            ./my-desktop-env.nix
            ./etc.nix
        ];

    # Name your host machine
    networking.hostName = "mymachine"; 

    # Set your time zone.
    time.timeZone = "Europe/Utrecht";

    # Enter keyboard layout
    services.xserver.layout = "us";
    services.xserver.xkbVariant = "altgr-intl";

    # Define user accounts
    users.users = 
        { 
            myuser = 
            {
                home = "/home/myuser";
                extraGroups = [ "wheel" "networkmanager" ];
                isNormalUser = true;
                uid = 1000;
            };
        };
    
    # Install some packages
    environment.systemPackages = 
            with pkgs; 
            [
                ddate
                testdisk
                zsh
            ]; 
 
    # Enable the OpenSSH daemon
    services.openssh.enable = true;
    
}

For inspiration a collection of configuration.nix by NixOS community members can be found in the Configs article.

Imperative Operations

In addition to declarative system configuration, NixOS offers imperative commands to manage user specific package management. These operations are managed by the nix-env command line tool. The following is a summary of some common operations that can be performed with it:

Searching for packages	nix-env -qaP '.*packagename.*'
Installing a package	nix-env -i packagename
List installed packages	nix-env -q
Uninstall packages	nix-env -e packagename
Upgrade packages	nix-env -u

See also

• NixOS Modules