forked from cadey/xesite
534 lines
18 KiB
Markdown
534 lines
18 KiB
Markdown
---
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title: "My NixOS Desktop Flow"
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date: 2020-04-25
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series: howto
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---
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# My NixOS Desktop Flow
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Before I built my current desktop, I had been using a [2013 Mac Pro][macpro2013]
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for at least 7 years. This machine has seen me through living in a few cities
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(Bellevue, Mountain View and Montreal), but it was starting to show its age. Its
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12 core Xeon is really no slouch (scoring about 5 minutes in my "compile the
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linux kernel" test), but with Intel security patches it was starting to get
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slower and slower as time went on.
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[macpro2013]: https://www.apple.com/mac-pro-2013/specs/
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So in March (just before the situation started) I ordered the parts for my new
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tower and built my current desktop machine. From the start, I wanted it to run
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Linux and have 64 GB of ram, mostly so I could write and test programs without
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having to worry about ram exhaustion.
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When the parts were almost in, I had decided to really start digging into
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[NixOS][nixos]. Friends on IRC and Discord had been trying to get me to use it
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for years, and I was really impressed with a simple setup that I had in a
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virtual machine. So I decided to jump head-first down that rabbit hole, and I'm
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honestly really glad I did.
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[nixos]: https://nixos.org
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NixOS is built on a more functional approach to package management called
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[Nix][nix]. Parts of the configuration can be easily broken off into modules
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that can be reused across machines in a deployment. If [Ansible][ansible] or
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other tools like it let you customize an existing Linux distribution to meet
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your needs, NixOS allows you to craft your own Linux distribution around your
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needs.
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[nix]: https://nixos.org/nix/
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[ansible]: https://www.ansible.com/
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Unfortunately, the Nix and NixOS documentation is a bit more dense than most
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other Linux programs/distributions are, and it's a bit easy to get lost in it.
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I'm going to attempt to explain a lot of the guiding principles behind Nix and
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NixOS and how they fit into how I use NixOS on my desktop.
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## What is a Package?
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Earlier, I mentioned that Nix is a _functional_ package manager. This means that
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Nix views packages as a combination of inputs to get an output:
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This is how most package managers work (even things like Windows installer
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files), but Nix goes a step further by disallowing package builds to access the
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internet. This allows Nix packages to be a lot more reproducible; meaning if you
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have the same inputs (source code, build script and patches) you should _always_
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get the same output byte-for-byte every time you build the same package at the
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same version.
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### A Simple Package
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Let's consider a simple example, my [gruvbox-inspired CSS file][gruvboxcss]'s
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[`default.nix`][gcssdefaultnix] file':
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[gruvboxcss]: https://github.com/Xe/gruvbox-css
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[gcssdefaultnix]: https://github.com/Xe/gruvbox-css/blob/master/default.nix
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```nix
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{ pkgs ? import <nixpkgs> { } }:
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pkgs.stdenv.mkDerivation {
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pname = "gruvbox-css";
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version = "latest";
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src = ./.;
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phases = "installPhase";
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installPhase = ''
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mkdir -p $out
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cp -rf $src/gruvbox.css $out/gruvbox.css
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'';
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}
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```
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This creates a package named `gruvbox-css` with the version `latest`. Let's
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break this down its `default.nix` line by line:
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```nix
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{ pkgs ? import <nixpkgs> { } }:
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```
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This creates a function that either takes in the `pkgs` object or tells Nix to
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import the standard package library [nixpkgs][nixpkgs] as `pkgs`. nixpkgs
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includes a lot of utilities like a standard packaging environment, special
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builders for things like snaps and Docker images as well as one of the largest
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package sets out there.
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[nixpkgs]: https://nixos.org/nixpkgs/
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```nix
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pkgs.stdenv.mkDerivation {
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# ...
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}
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```
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This runs the [`stdenv.mkDerivation`][mkderiv] function with some arguments in an
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object. The "standard environment" comes with tools like GCC, bash, coreutils,
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find, sed, grep, awk, tar, make, patch and all of the major compression tools.
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This means that our package builds can build C/C++ programs, copy files to the
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output, and extract downloaded source files by default. You can add other inputs
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to this environment if you need to, but for now it works as-is.
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[mkderiv]: https://nixos.org/nixpkgs/manual/#sec-using-stdenv
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Let's specify the name and version of this package:
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```nix
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pname = "gruvbox-css";
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version = "latest";
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```
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`pname` stands for "package name". It is combined with the version to create the
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resulting package name. In this case it would be `gruvbox-css-latest`.
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Let's tell Nix how to build this package:
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```nix
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src = ./.;
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phases = "installPhase";
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installPhase = ''
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mkdir -p $out
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cp -rf $src/gruvbox.css $out/gruvbox.css
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'';
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```
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The `src` attribute tells Nix where the source code of the package is stored.
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Sometimes this can be a URL to a compressed archive on the internet, sometimes
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it can be a git repo, but for now it's the current working directory `./.`.
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This is a CSS file, it doesn't make sense to have to build these, so we skip the
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build phase and tell Nix to directly install the package to its output folder:
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```shell
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mkdir -p $out
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cp -rf $src/gruvbox.css $out/gruvbox.css
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```
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This two-liner shell script creates the output directory (usually exposed as
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`$out`) and then copies `gruvbox.css` into it. When we run this through Nix
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with`nix-build`, we get output that looks something like this:
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```console
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$ nix-build ./default.nix
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these derivations will be built:
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/nix/store/c99n4ixraigf4jb0jfjxbkzicd79scpj-gruvbox-css.drv
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building '/nix/store/c99n4ixraigf4jb0jfjxbkzicd79scpj-gruvbox-css.drv'...
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installing
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/nix/store/ng5qnhwyrk9zaidjv00arhx787r0412s-gruvbox-css
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```
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And `/nix/store/ng5qnhwyrk9zaidjv00arhx787r0412s-gruvbox-css` is the output
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package. Looking at its contents with `ls`, we see this:
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```console
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$ ls /nix/store/ng5qnhwyrk9zaidjv00arhx787r0412s-gruvbox-css
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gruvbox.css
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```
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### A More Complicated Package
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For a more complicated package, let's look at the [build directions of the
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website you are reading right now][sitedefaultnix]:
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[sitedefaultnix]: https://github.com/Xe/site/blob/master/site.nix
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```nix
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{ pkgs ? import (import ./nix/sources.nix).nixpkgs }:
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with pkgs;
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assert lib.versionAtLeast go.version "1.13";
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buildGoPackage rec {
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pname = "christinewebsite";
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version = "latest";
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goPackagePath = "christine.website";
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src = ./.;
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goDeps = ./nix/deps.nix;
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allowGoReference = false;
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preBuild = ''
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export CGO_ENABLED=0
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buildFlagsArray+=(-pkgdir "$TMPDIR")
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'';
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postInstall = ''
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cp -rf $src/blog $bin/blog
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cp -rf $src/css $bin/css
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cp -rf $src/gallery $bin/gallery
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cp -rf $src/signalboost.dhall $bin/signalboost.dhall
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cp -rf $src/static $bin/static
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cp -rf $src/talks $bin/talks
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cp -rf $src/templates $bin/templates
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'';
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}
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```
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Breaking it down, we see some similarities to the gruvbox-css package from
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above, but there's a few more interesting lines I want to point out:
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```nix
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{ pkgs ? import (import ./nix/sources.nix).nixpkgs }:
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```
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My website uses a pinned or fixed version of nixpkgs. This allows my website's
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deployment to be stable even if nixpkgs changes something that could cause it to
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break.
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```nix
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with pkgs;
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```
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[With expressions][nixwith] are one of the more interesting parts of Nix.
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Essentially, they let you say "everything in this object should be put into
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scope". So if you have an expression that does this:
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[nixwith]: https://nixos.org/nix/manual/#idm140737321975440
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```nix
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let
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foo = {
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ponies = "awesome";
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};
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in with foo; "ponies are ${ponies}!"
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```
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You get the result `"ponies are awesome!"`. I use `with pkgs` here to use things
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directly from nixpkgs without having to say `pkgs.` in front of a lot of things.
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```nix
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assert lib.versionAtLeast go.version "1.13";
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```
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This line will make the build fail if Nix is using any Go version less than
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1.13. I'm pretty sure my website's code could function on older versions of Go,
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but the runtime improvements are important to it, so let's fail loudly just in
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case.
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```nix
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buildGoPackage {
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# ...
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}
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```
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[`buildGoPackage`](https://nixos.org/nixpkgs/manual/#ssec-go-legacy) builds a Go
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package into a Nix package. It takes in the [Go package path][gopkgpath], list
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of dependencies and if the resulting package is allowed to depend on the Go
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compiler or not.
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[gopkgpath]: https://github.com/golang/go/wiki/GOPATH#directory-layout
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It will then compile the Go program (and all of its dependencies) into a binary
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and put that in the resulting package. This website is more than just the source
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code, it's also got assets like CSS files and the image earlier in the post.
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Those files are copied in the `postInstall` phase:
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```nix
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postInstall = ''
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cp -rf $src/blog $bin/blog
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cp -rf $src/css $bin/css
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cp -rf $src/gallery $bin/gallery
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cp -rf $src/signalboost.dhall $bin/signalboost.dhall
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cp -rf $src/static $bin/static
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cp -rf $src/talks $bin/talks
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cp -rf $src/templates $bin/templates
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'';
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```
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This results in all of the files that my website needs to run existing in the
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right places.
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### Other Packages
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For more kinds of packages that you can build, see the [Languages and
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Frameworks][nixpkgslangsframeworks] chapter of the nixpkgs documentation.
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[nixpkgslangsframeworks]: https://nixos.org/nixpkgs/manual/#chap-language-support
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If your favorite language isn't shown there, you can make your own build script
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and do it more manually. See [here][nixpillscustombuilder] for more information
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on how to do that.
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[nixpillscustombuilder]: https://nixos.org/nixos/nix-pills/working-derivation.html#idm140737320334640
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## `nix-env` And Friends
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Building your own packages is nice and all, but what about using packages
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defined in nixpkgs? Nix includes a few tools that help you find, install,
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upgrade and remove packages as well as `nix-build` to build new ones.
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### `nix search`
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When looking for a package to install, use `$ nix search name` to see if it's
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already packaged. For example, let's look for [graphviz][graphviz], a popular
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diagramming software:
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[graphviz]: https://graphviz.org/
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```console
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$ nix search graphviz
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* nixos.graphviz (graphviz)
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Graph visualization tools
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* nixos.graphviz-nox (graphviz)
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Graph visualization tools
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* nixos.graphviz_2_32 (graphviz)
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Graph visualization tools
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```
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There are several results here! These are different because sometimes you may
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want some features of graphviz, but not all of them. For example, a server
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installation of graphviz wouldn't need X windows support.
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The first line of the output is the attribute. This is the attribute that the
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package is imported to inside nixpkgs. This allows multiple packages in
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different contexts to exist in nixpkgs at the same time, for example with python
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2 and python 3 versions of a library.
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The second line is a description of the package from its metadata section.
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The `nix` tool allows you to do a lot more than just this, but for now this is
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the most important thing.
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### `nix-env -i`
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`nix-env` is a rather big tool that does a lot of things (similar to pacman in
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Arch Linux), so I'm going to break things down into separate sections.
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Let's pick an instance graphviz from before and install it using `nix-env`:
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```console
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$ nix-env -iA nixos.graphviz
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installing 'graphviz-2.42.2'
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these paths will be fetched (5.00 MiB download, 13.74 MiB unpacked):
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/nix/store/980jk7qbcfrlnx8jsmdx92q96wsai8mx-gts-0.7.6
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/nix/store/fij1p8f0yjpv35n342ii9pwfahj8rlbb-graphviz-2.42.2
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/nix/store/jy35xihlnb3az0vdksyg9rd2f38q2c01-libdevil-1.7.8
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/nix/store/s895dnwlprwpfp75pzq70qzfdn8mwfzc-lcms-1.19
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copying path '/nix/store/980jk7qbcfrlnx8jsmdx92q96wsai8mx-gts-0.7.6' from 'https://cache.nixos.org'...
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copying path '/nix/store/s895dnwlprwpfp75pzq70qzfdn8mwfzc-lcms-1.19' from 'https://cache.nixos.org'...
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copying path '/nix/store/jy35xihlnb3az0vdksyg9rd2f38q2c01-libdevil-1.7.8' from 'https://cache.nixos.org'...
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copying path '/nix/store/fij1p8f0yjpv35n342ii9pwfahj8rlbb-graphviz-2.42.2' from 'https://cache.nixos.org'...
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building '/nix/store/r4fqdwpicqjpa97biis1jlxzb4ywi92b-user-environment.drv'...
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created 664 symlinks in user environment
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```
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And now let's see where the `dot` tool from graphviz is installed to:
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```console
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$ which dot
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/home/cadey/.nix-profile/bin/dot
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$ readlink /home/cadey/.nix-profile/bin/dot
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/nix/store/fij1p8f0yjpv35n342ii9pwfahj8rlbb-graphviz-2.42.2/bin/dot
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```
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This lets you install tools into the system-level Nix store without affecting
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other user's environments, even if they depend on a different version of
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graphviz.
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### `nix-env -e`
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`nix-env -e` lets you uninstall packages installed with `nix-env -i`. Let's
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uninstall graphviz:
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```console
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$ nix-env -e graphviz
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```
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Now the `dot` tool will be gone from your shell:
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```console
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$ which dot
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which: no dot in (/run/wrappers/bin:/home/cadey/.nix-profile/bin:/etc/profiles/per-user/cadey/bin:/nix/var/nix/profiles/default/bin:/run/current-system/sw/bin)
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```
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And it's like graphviz was never installed.
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Notice that these package management commands are done at the _user_ level
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because they are only affecting the currently logged-in user. This allows users
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to install their own editors or other tools without having to get admins
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involved.
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## Adding up to NixOS
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NixOS builds on top of Nix and its command line tools to make an entire Linux
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distribution that can be perfectly crafted to your needs. NixOS machines are
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configured using a [configuration.nix][confignix] file that contains the
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following kinds of settings:
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[confignix]: https://nixos.org/nixos/manual/index.html#ch-configuration
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- packages installed to the system
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- user accounts on the system
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- allowed SSH public keys for users on the system
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- services activated on the system
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- configuration for services on the system
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- magic unix flags like the number of allowed file descriptors per process
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- what drives to mount where
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- network configuration
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- ACME certificates
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[and so much more](https://nixos.org/nixos/options.html#)
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At a high level, machines are configured by setting options like this:
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```
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# basic-lxc-image.nix
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{ config, pkgs, ... }:
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{
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networking.hostName = "example-for-blog";
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environment.systemPackages = with pkgs; [ wget vim ];
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}
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```
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This would specify a simple NixOS machine with the hostname `example-for-blog`
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and with wget and vim installed. This is nowhere near enough to boot an entire
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system, but is good enough for describing the base layout of a basic [LXC][lxc]
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image.
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[lxc]: https://linuxcontainers.org/lxc/introduction/
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For a more complete example of NixOS configurations, see
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[here](https://github.com/Xe/nixos-configs/tree/master/hosts) or repositories on
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[this handy NixOS wiki page](https://nixos.wiki/wiki/Configuration_Collection).
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The main configuration.nix file (usually at `/etc/nixos/configuration.nix`) can also
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import other NixOS modules using the `imports` attribute:
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```nix
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# better-vm.nix
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{ config, pkgs, ... }:
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{
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imports = [
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./basic-lxc-image.nix
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];
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networking.hostName = "better-vm";
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services.nginx.enable = true;
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}
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```
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And the `better-vm.nix` file would describe a machine with the hostname
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`better-vm` that has wget and vim installed, but is also running nginx with its
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default configuration.
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Internally, every one of these options will be fed into auto-generated Nix
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packages that will describe the system configuration bit by bit.
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### `nixos-rebuild`
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One of the handy features about Nix is that every package exists in its own part
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of the Nix store. This allows you to leave the older versions of a package
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laying around so you can roll back to them if you need to. `nixos-rebuild` is
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the tool that helps you commit configuration changes to the system as well as
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roll them back.
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If you want to upgrade your entire system:
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```console
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$ sudo nixos-rebuild switch --upgrade
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```
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This tells nixos-rebuild to upgrade the package channels, use those to create a
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new base system description, switch the running system to it and start/restart/stop
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any services that were added/upgraded/removed during the upgrade. Every time you
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rebuild the configuration, you create a new "generation" of configuration that
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you can roll back to just as easily:
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```console
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$ sudo nixos-rebuild switch --rollback
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```
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### Garbage Collection
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As upgrades happen and old generations pile up, this may end up taking up a lot
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of unwanted disk (and boot menu) space. To free up this space, you can use
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`nix-collect-garbage`:
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```console
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$ sudo nix-collect-garbage
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< cleans up packages not referenced by anything >
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$ sudo nix-collect-garbage -d
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< deletes old generations and then cleans up packages not referenced by anything >
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```
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The latter is a fairly powerful command and can wipe out older system states.
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Only run this if you are sure you don't want to go back to an older setup.
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## How I Use It
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Each of these things builds on top of eachother to make the base platform that I
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built my desktop environment on. I have the configuration for [my
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shell][xefish], [emacs][xemacs], [my window manager][xedwm] and just about [every
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program I use on a regular basis][xecommon] defined in their own NixOS modules so I can
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pick and choose things for new machines.
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[xefish]: https://github.com/Xe/xepkgs/tree/master/modules/fish
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[xemacs]: https://github.com/Xe/nixos-configs/tree/master/common/users/cadey/spacemacs
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[xedwm]: https://github.com/Xe/xepkgs/tree/master/modules/dwm
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[xecommon]: https://github.com/Xe/nixos-configs/tree/master/common
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When I want to change part of my config, I edit the files responsible for that
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|
part of the config and then rebuild the system to test it. If things work
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properly, I commit those changes and then continue using the system like normal.
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This is a little bit more work in the short term, but as a result I get a setup
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that is easier to recreate on more machines in the future. It took me a half
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hour or so to get the configuration for [zathura][zathura] right, but now I have
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[a zathura
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module](https://github.com/Xe/nixos-configs/tree/master/common/users/cadey/zathura)
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that lets me get exactly the setup I want every time.
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[zathura]: https://pwmt.org/projects/zathura/
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## TL;DR
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Nix and NixOS ruined me. It's hard to go back.
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