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% NixOS First steps % サニエ エリック % 2016年12月07日 - Tokyo NixOS Meetup

First Steps

  • Understanding NixOS structure
  • Get familiar with NixOS
    • Configuration File
    • Channels
  • Maintenance

NixOS Overview

  • Uses Nix as a package manager
  • Source and binary packages
  • A single configuration file controls the OS
  • System versioning and rollbacks
  • Multi-user package management
  • Separation of environments and filesystem (via profiles)

NixOS Structure

  • configuration.nix:
    • Configuration file that manage every aspect of the OS
  • Nix Store:
    • Where all Nix products are stored
  • nixpkgs:
    • Collection of Nix packages "recipes" and NixOS modules definitions
  • Channels:
    • Way to synchronize nixpkgs
  • Profiles:
    • Way to manage environments, per user, revisioned

Configuration file

  • Located /etc/nixos/configuration.nix
    • written in Nix Expression Language
    • functional language, close to untyped lambda calculus
    • can be splitted in multiple files via imports
  • NixOS modules
    • modules define options
    • options are used in configuration.nix
  • Thousands of options
    • can even configure vim

Configuration file

  • Provisioning with environment.systemPackages
  • services, programs, setting files, boot, kernel modules, users, ...
  • Possible to import custom modules with imports
  • man configuration.nix, nixos-option, nixos-help commands
  • Links:

Configuration tricks

  • Overriding packages dependencies:

    environment.systemPackages = with pkgs; [
  (nginx.override { openssl = libressl; })
];

  • Using custom packages:

    environment.systemPackages = with pkgs; [
  (import ./my-pkg.nix)
  (pkgs.callPackage ./my-other-pkg.nix)
];

Applying configuration

  • nixos-rebuild command
    • nixos-rebuild switch: rebuild, activate the configuration and add it to the boot menu.
    • nixos-rebuild test: rebuild, activate the configuration but don't add it to the boot menu.
    • nixos-rebuild build-vm: create a QEMU virtual machine with the configuration.
    • -I nixos-config=/etc/nixos/custom-configuration.nix to use a different configuration file.
    • -I nixpkgs=/path/to/nixpkgs to use a custom version of nixpkgs.

Nix store

  • Location /nix/store/

  • Contains:

    • Every builded package
    • Every channel version
    • Every profile

  • Every store item is compartimented in its own folder

  • Example:

    $ nix-build -A hello '<nixpkgs>'
$ ls result -dl
$ tree result

nixpkgs

Channels

  • External point of view: Channels are a way to distribute specific versions of nixpkgs
  • Internal point of view: Channels are a way to sync nixpkgs that meet some requirements
  • Version of nixpkgs to use, multiple variants:
    • *-XX.XX: stable channels, new one every 6 months
    • *-unstable: unstable channels, close to rolling release
    • *-small: small channels, good for servers

nix-channel command

  • nix-channel command to manipulate channels

    • nix-channel --list list used channels
    • nix-channel --add to add a channel
    • nix-channel --update to update the channels

  • Example: using the unstable channel:

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

  • Channels information is stored in ~/.nix-channels

  • Active channels are linked in ~/.nix-defexpr/

  • All channels and their versions are stored under /nix/var/nix/profiles/per-user

  • root user channel is the system channel (used by nixos-rebuild)

Channel tricks

  • A remote nixpkgs archive can be used:

    $ nixos-rebuild switch -I nixpkgs=https://github.com/nixos/nixpkgs-channels/archive/nixos-16.09.tar.gz

  • A local checkout of nixpkgs, useful for custom patches:

    $ nixos-rebuild switch -I nixpkgs=/path/to/my/nixpkgs

Channel rollback

  • User channels version can be checked with:

    $ nix-env -p /nix/var/nix/profiles/per-user/USER/channels --list-generations

  • And their version changed with:

    $ nix-env -p /nix/var/nix/profiles/per-user/USER/channels --switch-generations GEN

Profiles

  • Profiles merge nix-store paths by symbolic links
  • Active profile is in ~/.nix-profile
    • Profiles are managed and versioned in /nix/var/nix/profiles/per-user
  • configuration.nix environment.systemPackages profile is linked to /run/current-system/sw
  • Links:

Trying software

  • nix-shell command to generate temporary environments:

    $ nix-shell -p hello
$ hello

  • can even run commands:

    $ nix-shell -p cowsay --run "cowsay hello nix"

  • nix-shells can be declared in nix-files, handy for setting dev environments

  • nix-shell can also be used as shebang

Finding software

  • nix-env is complex, nox is more user-friendly:

    $ nix-shell -p nox
$ nox browser

Maintenance

  • Watch for the store size!

  • Nix store all the packages in the nix store (/nix/store)

  • Removing packages with nix-env -e or by removing them from environment.systemPackages dont remove them from the store

  • Store can be cleaned by garbage-collecting it:

    # nix-collect-garbage --delete-older-than 14d