NixOS: the foundations of a declarative system

What is NixOS?#

NixOS is a Linux distribution based on the Nix package manager, developed and maintained by the NixOS Foundation. Its distinctive declarative configuration approach lets you define and manage the entire system through configuration files.

Core features#

1. Declarative configuration

Traditional Linux distributions usually require you to install packages, edit configuration files, and enable services manually. In NixOS, all these operations are defined in a single configuration.nix file:

{ config, pkgs, ... }:

{
  # 启用 OpenSSH 服务
  services.openssh.enable = true;
  
  # 安装软件包
  environment.systemPackages = with pkgs; [
    vim
    git
    htop
  ];
  
  # 配置用户
  users.users.alice = {
    isNormalUser = true;
    extraGroups = [ "wheel" ];
  };
}

2. Reproducibility

Pinning the configuration, dependency revisions, and build inputs lets you repeatedly build the system environment described by the declaration. Writable data, hardware differences, and nondeterministic builds still need separate handling. This means:

• You can deploy the same declarative environment on different machines
• Team development environments can stay consistent
• Production and development environments can share the same dependency and configuration definitions

3. Atomic upgrades & rollbacks

NixOS system updates are atomic:

• New build outputs do not overwrite old ones, and switching the system profile supports atomic updates
• Activation scripts, service restarts, bootloaders, and writable data can still encounter failures; rollback is no substitute for backups
• You can roll back to a previous working version at any time

# 查看可回滚的系统版本
sudo nixos-rebuild list-generations

# 切换到特定版本
sudo nix-env --profile /nix/var/nix/profiles/system --switch-generation 42
sudo /nix/var/nix/profiles/system/bin/switch-to-configuration switch

switch activates the configuration immediately and makes it the boot default; boot only builds it and makes it the boot default, leaving the running system unchanged; test activates it immediately without adding it to the boot menu. NixOS Manual

When replacing a login manager or critical service, both switch and test may interrupt the current session. If you want the new configuration to apply at the next boot, you can use boot first:

sudo nixos-rebuild boot --flake .#workstation
# 确认工作已保存后才重启
sudo systemctl reboot

4. Reliable package management

Features of the Nix package manager:

• Isolated package paths: different packages and versions do not overwrite one another; activation and program execution can still have side effects
• Coexisting versions: different versions of the same software can exist at the same time
• Garbage collection: automatically removes packages no longer in use
• Binary caches: prebuilt packages can be installed quickly

Where NixOS fits#

NixOS architecture#

┌─────────────────────────────────────┐
│          用户空间应用层              │
│    (桌面环境、浏览器、编辑器等)       │
├─────────────────────────────────────┤
│          系统服务层                  │
│    (systemd 服务、网络服务等)         │
├─────────────────────────────────────┤
│          NixOS 配置层                │
│    (configuration.nix)               │
├─────────────────────────────────────┤
│          Nix 包管理器                │
│    (nixpkgs、flakes)                 │
├─────────────────────────────────────┤
│          Linux 内核                  │
└─────────────────────────────────────┘

Learning recommendations#

Learning NixOS requires an understanding of the following:

1. Nix language basics - for writing configuration files
2. The NixOS module system - how configuration options work
3. nixpkgs - how to use the Nix package collection
4. Flakes - Nix's next-generation project-management tools

Comparison with other Linux distributions#

Further resources#

• Official NixOS website
• Official nix.dev tutorials
• NixOS Chinese community
• NixOS Manual