nix-git/NixOS.md

# NixOS

This document contains general notes about NixOS that are independent of my NixOS configuration.

## Table of Contents

<!-- TOC -->
* [NixOS](#nixos)
  * [Table of Contents](#table-of-contents)
  * [Misc](#misc)
  * [NixOS upgrades](#nixos-upgrades)
  * [niv: Dependency management](#niv-dependency-management)
    * [Add Home Manager with niv](#add-home-manager-with-niv)
    * [Add NUR with niv](#add-nur-with-niv)
  * [System information](#system-information)
  * [Customize a NixOS package with override or nix-build](#customize-a-nixos-package-with-override-or-nix-build)
  * [Search for packages](#search-for-packages)
  * [Search for options](#search-for-options)
  * [Search which package owns a file](#search-which-package-owns-a-file)
  * [List files of package](#list-files-of-package)
  * [Package runtime dependency report](#package-runtime-dependency-report)
  * [Nix profiles](#nix-profiles)
    * [Switch to previous system profile](#switch-to-previous-system-profile)
    * [List system profiles](#list-system-profiles)
    * [Deleting generations - Keep most recent X system profiles](#deleting-generations---keep-most-recent-x-system-profiles)
    * [Garbage collection - Delete unreachable store objects](#garbage-collection---delete-unreachable-store-objects)
    * [List installed packages](#list-installed-packages)
    * [why-depends: Why is a package installed](#why-depends-why-is-a-package-installed)
    * [Compare two system profiles](#compare-two-system-profiles)
  * [NixOS configuration debugging](#nixos-configuration-debugging)
  * [Show Nix configuration](#show-nix-configuration)
  * [Evaluate NixOS configuration to JSON](#evaluate-nixos-configuration-to-json)
  * [Evaluate expressions in the context of a NixOS configuration managed with Colmena](#evaluate-expressions-in-the-context-of-a-nixos-configuration-managed-with-colmena)
  * [Evaluate expressions](#evaluate-expressions)
  * [Escape strings](#escape-strings)
  * [Run AppImages](#run-appimages)
  * [Audio troubleshooting - Realtek ALC898 Audio Codec on ASRock Z77 Extreme 4](#audio-troubleshooting---realtek-alc898-audio-codec-on-asrock-z77-extreme-4)
  * [Graphic drivers](#graphic-drivers)
  * [XDG mimes, desktop files](#xdg-mimes-desktop-files)
  * [Additional resources](#additional-resources)
    * [Nix Pills](#nix-pills)
    * [Papers](#papers)
<!-- TOC -->

## Misc

* There is controversy about flakes, rather use channels (e.g. with niv)

## NixOS upgrades

See [NixOS Upgrades](NixOS%20Upgrades.md).

## niv: Dependency management

* https://nix.dev/tutorials/first-steps/towards-reproducibility-pinning-nixpkgs#dependency-management-with-niv

niv:

> Easy dependency management for Nix projects.
>
> Nix is a very powerful tool for building code and setting up environments. niv complements it by making it easy to
> describe and update remote dependencies (URLs, GitHub repos, etc). It is a simple, practical alternative to Nix
> flakes.
>
> https://github.com/nmattia/niv

> Niv is an easy dependency management for Nix projects with package pinning.
>
> https://github.com/mikeroyal/NixOS-Guide

Initialize:

```shell
niv init
```

Change the tracking branch of nixpkgs from `unstable` to `24.11`:

```shell
niv modify nixpkgs --branch nixos-24.11
```

Add nixpkgs `unstable`:

```shell
niv add NixOS/nixpkgs -n unstable -b nixpkgs-unstable
```

### Add Home Manager with niv

Home Manager:

> [Home Manager] allows declarative configuration of user specific (non-global) packages and dotfiles.
>
> To avoid breaking users' configurations, Home Manager is released in branches corresponding to NixOS releases (
> e.g. `release-24.11`).
>
> Home Manager provides both the channel-based setup and the flake-based one.
>
> https://github.com/nix-community/home-manager

Check your channel:

```shell
sudo nix-channel --list
#=> nixos https://nixos.org/channels/nixos-24.11
```

Use the corresponding branch:

```shell
niv add nix-community/home-manager -n home-manager -b release-24.11
```

### Add NUR with niv

> The Nix User Repository (NUR) is community-driven meta repository for Nix packages.
>
> ... packages are built from source and are not reviewed by any Nixpkgs member.
>
> https://github.com/nix-community/NUR

```shell
niv add nix-community/NUR -n NUR
```

## System information

```shell
nix-info -m
```
```
 - system: `"x86_64-linux"`
 - host os: `Linux 6.12.7, NixOS, 24.11 (Vicuna), 24.11pre-git`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.24.11`
 - channels(root): `"nixos-24.11, unstable"`
 - channels(yoda): `""`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`
```

## Customize a NixOS package with override or nix-build

See https://codeberg.org/privacy1st/nix-build-and-override-docs

## Search for packages

* https://search.nixos.org/packages

## Search for options

* https://search.nixos.org/options
    * Or `man configuration.nix`
* https://mipmip.github.io/home-manager-option-search
    * Or `man home-configuration.nix`

## Search which package owns a file

```shell
# Note how your shell prefix changes.
nix-shell -p nix-index
```
```shell
# Either build the index manually (requires >12GB RAM):
nix-index
# Or download weekly build:
mkdir -p ~/.cache/nix-index/ && wget -q -N https://github.com/nix-community/nix-index-database/releases/latest/download/index-x86_64-linux -O ~/.cache/nix-index/files

# Then search for a file
nix-locate --whole-name '/bash'
```

## List files of package

* https://discourse.nixos.org/t/list-files-of-package/25830/2

Example for `nano`:

```shell
find $(nix-build '<nixpkgs>' -A nano --no-link)
```

Excerpt of the result:

```
/nix/store/jqvxmx65mfinbsm6db9kmcqmphl44xhp-nano-7.2/share/nano
/nix/store/jqvxmx65mfinbsm6db9kmcqmphl44xhp-nano-7.2/share/nano/asm.nanorc
/nix/store/jqvxmx65mfinbsm6db9kmcqmphl44xhp-nano-7.2/share/nano/autoconf.nanorc
```

## Package runtime dependency report

- https://github.com/nix-how/nix-demos#runtimereport -> https://www.nmattia.com/posts/2019-10-08-runtime-dependencies/

Example: Licenses and maintainers of runtime dependencies of package `hello`:

```shell
nix --extra-experimental-features flakes --extra-experimental-features nix-command bundle --bundler github:nix-how/nix-demos#runtimeReport nixpkgs#hello
cat hello-*-report
```
```console
  ---------------------------------
  |        OFFICIAL REPORT        |
  |   requested by: the lawyers   |
  |    written by: yours truly    |
  |    TOP SECRET - TOP SECRET    |
  ---------------------------------

runtime dependencies of hello-2.12.1:
 - libunistring-1.1 (lgpl3Plus) maintained by 
 - xgcc-13.2.0 (gpl3Plus) maintained by Patrick Hilhorst, Vladimír Čunát, John Ericson
 - hello-2.12.1 (gpl3Plus) maintained by Eelco Dolstra
 - libidn2-2.3.4 (lgpl3Plus, gpl2Plus, gpl3Plus) maintained by Franz Pletz
 - glibc-2.38-27 (lgpl2Plus) maintained by Eelco Dolstra, Maximilian Bosch, Connor Baker
```

Example: `nano`

```console
  ---------------------------------
  |        OFFICIAL REPORT        |
  |   requested by: the lawyers   |
  |    written by: yours truly    |
  |    TOP SECRET - TOP SECRET    |
  ---------------------------------

runtime dependencies of nano-7.2:
 - libunistring-1.1 (lgpl3Plus) maintained by 
 - file-5.45 (bsd2) maintained by Doron Behar
 - xgcc-13.2.0 (gpl3Plus) maintained by Patrick Hilhorst, Vladimír Čunát, John Ericson
 - nano-7.2 (gpl3Plus) maintained by Joachim Fasting, Tim Steinbach
 - libidn2-2.3.4 (lgpl3Plus, gpl2Plus, gpl3Plus) maintained by Franz Pletz
 - zlib-1.3 (zlib) maintained by nobody
 - glibc-2.38-27 (lgpl2Plus) maintained by Eelco Dolstra, Maximilian Bosch, Connor Baker
 - ncurses-6.4 (mit) maintained by nobody
```

Example: `firefox`

```console
  ---------------------------------
  |        OFFICIAL REPORT        |
  |   requested by: the lawyers   |
  |    written by: yours truly    |
  |    TOP SECRET - TOP SECRET    |
  ---------------------------------

runtime dependencies of firefox-121.0.1:
 - libunistring-1.1 (lgpl3Plus) maintained by 
 - perl5.38.2-WWW-RobotRules-6.02 (artistic1, gpl1Plus) maintained by nobody
 - gdbm-1.23 (gpl3Plus) maintained by Rahul Gopinath
 - perl5.38.2-HTTP-CookieJar-0.014 (asl20) maintained by nobody
 - gmp-with-cxx-6.3.0 (lgpl3Only, gpl2Only) maintained by Rahul Gopinath
 - libXdamage-1.1.6 (no license) maintained by nobody
 - expat-2.5.0 (mit) maintained by nobody
 - gnutls-3.8.2 (lgpl21Plus) maintained by Vladimír Čunát
 - dbus-1.14.10 (gpl2Plus) maintained by Jan Tojnar
 - systemd-minimal-libs-254.6 (lgpl21Plus) maintained by Florian Klink, Finn Behrens
 - gnutar-1.35 (gpl3Plus) maintained by 
 - util-linux-minimal-2.39.3 (gpl2Only, gpl2Plus, gpl3Plus, lgpl21Plus, bsd3, bsdOriginalUC, publicDomain) maintained by nobody
 - gdk-pixbuf-2.42.10 (lgpl21Plus) maintained by Eelco Dolstra, Bobby Rong, Tor Hedin Brønner, Jan Tojnar, Daniel Șerbănescu, Maxine Aubrey
 - tracker-3.6.0 (gpl2Plus) maintained by Bobby Rong, Tor Hedin Brønner, Jan Tojnar, Daniel Șerbănescu, Maxine Aubrey
 - libXext-1.3.5 (no license) maintained by nobody
 - openssl-3.0.12 (asl20) maintained by Markus Theil
 - at-spi2-core-2.50.0 (lgpl21Plus) maintained by Bobby Rong, Tor Hedin Brønner, Jan Tojnar, Daniel Șerbănescu, Maxine Aubrey, Michael Raskin
 - libXtst-1.2.4 (no license) maintained by nobody
 - gcc-13.2.0 (gpl3Plus) maintained by Patrick Hilhorst, Vladimír Čunát, John Ericson
 - bzip2-1.0.8 (bsdOriginal) maintained by Jörg Thalheim
 - perl5.38.2-TimeDate-2.33 (artistic1, gpl1Plus) maintained by nobody
 - libsoup-3.4.4 (lgpl2Plus) maintained by Bobby Rong, Tor Hedin Brønner, Jan Tojnar, Daniel Șerbănescu, Maxine Aubrey, Jason O'Conal, Michael Raskin
 - dconf-0.40.0 (lgpl21Plus) maintained by Bobby Rong, Tor Hedin Brønner, Jan Tojnar, Daniel Șerbănescu, Maxine Aubrey
 - cairo-1.18.0 (lgpl2Plus, mpl10) maintained by nobody
 - libxcrypt-4.4.36 (lgpl21Plus) maintained by Misha Gusarov, Martin Weinelt
 - libxml2-2.12.3-unstable-2023-12-14 (mit) maintained by Eelco Dolstra, Jan Tojnar
 - libffi-3.4.4 (mit) maintained by Matthew Bauer
 - perl5.38.2-Test-Fatal-0.017 (artistic1, gpl1Plus) maintained by nobody
 - gcc-13.2.0 (gpl3Plus) maintained by Patrick Hilhorst, Vladimír Čunát, John Ericson
 - libnetfilter_conntrack-1.0.9 (gpl2Plus) maintained by nobody
 - shadow-4.14.2 (bsd3) maintained by nobody
 - util-linux-minimal-2.39.3 (gpl2Only, gpl2Plus, gpl3Plus, lgpl21Plus, bsd3, bsdOriginalUC, publicDomain) maintained by nobody
 - zstd-1.5.5 (bsd3) maintained by Orivej Desh
 - libyaml-0.2.5 (mit) maintained by nobody
 - db-4.8.30 (sleepycat) maintained by nobody
 - json-c-0.17 (mit) maintained by Jason O'Conal
 - avahi-0.8 (lgpl2Plus) maintained by Jason O'Conal, Robin Gloster
 - libXfixes-6.0.1 (no license) maintained by nobody
 - libsoup-2.74.3 (lgpl2Plus) maintained by Bobby Rong, Tor Hedin Brønner, Jan Tojnar, Daniel Șerbănescu, Maxine Aubrey, Jason O'Conal, Michael Raskin
 - libapparmor-3.1.6 (gpl2Only, lgpl21Only) maintained by Julien Moutinho, Austin Seipp, Andreas Schrägle, Janne Heß
 - cups-2.4.7 (asl20) maintained by Matthew Bauer
 - wayland-1.22.0 (mit) maintained by Michael Weiss, Cody Opel, Alyssa Ross
 - libXrandr-1.5.4 (no license) maintained by nobody
 - cryptsetup-2.6.1 (gpl2) maintained by Ryan Lahfa
 - nghttp2-1.57.0 (mit) maintained by Renaud
 - file-5.45 (bsd2) maintained by Doron Behar
 - gtk+3-3.24.39 (lgpl2Plus) maintained by Michael Raskin, Bobby Rong, Tor Hedin Brønner, Jan Tojnar, Daniel Șerbănescu, Maxine Aubrey
 - giflib-5.2.1 (mit) maintained by 
 - gmp-with-cxx-6.3.0 (lgpl3Only, gpl2Only) maintained by Rahul Gopinath
 - libselinux-3.3 (gpl2Plus) maintained by 
 - freetype-2.13.2 (gpl2Plus) maintained by Thomas Tuegel
 - graphite2-1.3.14 (lgpl21) maintained by Michael Raskin
 - bash-5.2-p21 (gpl3Plus) maintained by Will Dietz
 - perl5.38.2-Net-HTTP-6.23 (artistic1, gpl1Plus) maintained by nobody
 - xkeyboard-config-2.40 (no license) maintained by nobody
 - audit-3.1.2 (gpl2Plus) maintained by Anderson Torres
 - libXrender-0.9.11 (no license) maintained by nobody
 - gnum4-1.4.19 (gpl3Plus) maintained by nobody
 - libdeflate-1.19 (mit) maintained by Orivej Desh, Dmitry Bogatov
 - perl5.38.2-HTTP-Cookies-6.10 (artistic1, gpl1Plus) maintained by nobody
 - fribidi-1.0.13 (lgpl21) maintained by nobody
 - libfido2-1.14.0 (bsd2) maintained by Will Dietz, Pavol Rusnak
 - libuv-1.47.0 (mit, isc, bsd2, bsd3, cc-by-40) maintained by Mario Rodas
 - python3-3.11.7 (psfl) maintained by Frederik Rietdijk
 - xgcc-13.2.0 (gpl3Plus) maintained by Patrick Hilhorst, Vladimír Čunát, John Ericson
 - libmnl-1.0.5 (lgpl21Plus) maintained by nobody
 - util-linux-minimal-2.39.3 (gpl2Only, gpl2Plus, gpl3Plus, lgpl21Plus, bsd3, bsdOriginalUC, publicDomain) maintained by nobody
 - libthai-0.1.29 (lgpl21Plus) maintained by 
 - gawk-5.2.2 (gpl3Plus) maintained by 
 - libXmu-1.1.4 (no license) maintained by nobody
 - unbound-1.19.0 (bsd3) maintained by Andreas Schrägle, Janne Heß
 - perl5.38.2-HTTP-Message-6.45 (artistic1, gpl1Plus) maintained by nobody
 - libbpf-1.3.0 (lgpl21, bsd2) maintained by Austin Seipp, Vladimír Čunát, Sascha Grunert, Dominique Martinet
 - pixman-0.42.2 (mit) maintained by nobody
 - libXft-2.3.8 (no license) maintained by nobody
 - libGL-1.7.0 (mit, bsd1, bsd3, gpl3Only, asl20) maintained by nobody
 - firefox-121.0.1 (mpl20) maintained by Bernardo Meurer, Martin Weinelt
 - util-linux-minimal-2.39.3 (gpl2Only, gpl2Plus, gpl3Plus, lgpl21Plus, bsd3, bsdOriginalUC, publicDomain) maintained by nobody
 - perl5.38.2-Clone-0.46 (artistic1, gpl1Plus) maintained by nobody
 - iptables-1.8.10 (gpl2) maintained by Franz Pletz
 - libssh2-1.11.0 (bsd3, libssh2) maintained by Sandro Jäckel
 - systemd-minimal-254.6 (lgpl21Plus) maintained by Florian Klink, Finn Behrens
 - icu4c-73.2 (no license) maintained by Michael Raskin
 - pango-1.51.0 (lgpl2Plus) maintained by Michael Raskin, Bobby Rong, Tor Hedin Brønner, Jan Tojnar, Daniel Șerbănescu, Maxine Aubrey
 - libmicrohttpd-0.9.71 (lgpl2Plus) maintained by Eelco Dolstra, Rahul Gopinath, Franz Pletz
 - libcbor-unstable-2023-01-29 (mit) maintained by Will Dietz
 - attr-2.5.1 (gpl2Plus) maintained by nobody
 - perl5.38.2-HTML-Parser-3.81 (artistic1, gpl1Plus) maintained by nobody
 - libSM-1.2.4 (no license) maintained by nobody
 - libpng-apng-1.6.40 (libpng2) maintained by Vladimír Čunát
 - glib-2.78.3 (lgpl21Plus) maintained by Bobby Rong, Tor Hedin Brønner, Jan Tojnar, Daniel Șerbănescu, Maxine Aubrey, Jason O'Conal, Michael Raskin
 - gsettings-desktop-schemas-45.0 (lgpl21Plus) maintained by Bobby Rong, Tor Hedin Brønner, Jan Tojnar, Daniel Șerbănescu, Maxine Aubrey
 - nettle-3.9.1 (gpl2Plus) maintained by Vladimír Čunát
 - perl5.38.2-HTTP-Date-6.06 (artistic1, gpl1Plus) maintained by nobody
 - libusb-1.0.26 (lgpl21Plus) maintained by Pavol Rusnak, Ido Samuelson
 - libargon2-20190702 (asl20, cc0) maintained by Taeer Bar-Yam, Owen Lynch
 - brotli-1.1.0 (mit) maintained by freezeboy
 - glibc-2.38-27 (lgpl2Plus) maintained by Eelco Dolstra, Maximilian Bosch, Connor Baker
 - libcap-ng-0.8.3 (lgpl21) maintained by nobody
 - libnftnl-1.2.6 (gpl2Plus) maintained by Franz Pletz, Andreas Schrägle, Janne Heß
 - libxcb-1.16 (no license) maintained by nobody
 - glibc-2.38-27 (lgpl2Plus) maintained by Eelco Dolstra, Maximilian Bosch, Connor Baker
 - libpcap-1.10.4 (bsd3) maintained by Franz Pletz
 - libXt-1.3.0 (no license) maintained by nobody
 - publicsuffix-list-unstable-2023-02-16 (mpl20) maintained by Renaud
 - libepoxy-1.5.10 (mit) maintained by Cillian de Róiste
 - libX11-1.8.7 (no license) maintained by nobody
 - keyutils-1.6.3 (gpl2Plus) maintained by nobody
 - libXcursor-1.2.1 (no license) maintained by nobody
 - fontconfig-2.14.2 (bsd2) maintained by Jan Tojnar
 - tzdata-2023d (bsd3, publicDomain) maintained by Andreas Schrägle, Franz Pletz
 - tpm2-tss-4.0.1 (bsd2) maintained by Arthur Gautier
 - libxkbcommon-1.5.0 (mit) maintained by Michael Weiss, Thomas Tuegel
 - bash-interactive-5.2-p21 (gpl3Plus) maintained by Will Dietz
 - sqlite-3.44.2 (publicDomain) maintained by Eelco Dolstra, Nicolas Pouillard
 - perl5.38.2-XML-Parser-2.46 (artistic1, gpl1Plus) maintained by nobody
 - perl5.38.2-HTTP-Daemon-6.16 (artistic1, gpl1Plus) maintained by nobody
 - getent-glibc-2.38-27 (no license) maintained by nobody
 - libcap-2.69 (bsd3) maintained by nobody
 - xz-5.4.5 (gpl2Plus, lgpl21Plus) maintained by Sander van der Burg
 - perl5.38.2-Test-Needs-0.002010 (artistic1, gpl1Plus) maintained by nobody
 - perl5.38.2-File-Listing-6.16 (artistic1, gpl1Plus) maintained by nobody
 - libdatrie-2019-12-20 (lgpl21Plus) maintained by 
 - readline-8.2p7 (gpl3Plus) maintained by Will Dietz
 - libXcomposite-0.4.6 (no license) maintained by nobody
 - perl5.38.2-IO-HTML-1.004 (artistic1, gpl1Plus) maintained by nobody
 - coreutils-9.4 (gpl3Plus) maintained by Janne Heß
 - dejavu-fonts-minimal-2.37 (free) maintained by nobody
 - glib-2.78.3 (lgpl21Plus) maintained by Bobby Rong, Tor Hedin Brønner, Jan Tojnar, Daniel Șerbănescu, Maxine Aubrey, Jason O'Conal, Michael Raskin
 - libpsl-0.21.2 (mit) maintained by Renaud
 - libgpg-error-1.47 (lgpl2Plus) maintained by Rahul Gopinath
 - libnl-3.8.0 (lgpl21) maintained by Franz Pletz
 - openssl-3.0.12 (asl20) maintained by Markus Theil
 - pcre-8.45 (bsd3) maintained by 
 - perl5.38.2-Try-Tiny-0.31 (mit) maintained by nobody
 - libidn2-2.3.4 (lgpl3Plus, gpl2Plus, gpl3Plus) maintained by Franz Pletz
 - libtool-2.4.7 (gpl2Plus) maintained by 
 - p11-kit-0.25.3 (bsd3) maintained by nobody
 - harfbuzz-7.3.0 (mit) maintained by Eelco Dolstra
 - gnugrep-3.11 (gpl3Plus) maintained by Janne Heß, Moritz Lumme
 - zlib-1.3 (zlib) maintained by nobody
 - gnused-4.9 (gpl3Plus) maintained by Jörg Thalheim
 - libXdmcp-1.1.4 (no license) maintained by nobody
 - libnfnetlink-1.0.2 (gpl2) maintained by nobody
 - libevent-2.1.12 (bsd3) maintained by nobody
 - libICE-1.1.1 (no license) maintained by nobody
 - libmd-1.1.0 (bsd3, bsd2, isc, beerware, publicDomain) maintained by Michael Weiss
 - lvm2-2.03.22 (gpl2, bsd2, lgpl21) maintained by Michael Raskin, Andreas Schrägle, Janne Heß
 - lz4-1.9.4 (bsd2, gpl2Plus) maintained by nobody
 - glibc-2.38-27 (lgpl2Plus) maintained by Eelco Dolstra, Maximilian Bosch, Connor Baker
 - libdaemon-0.14 (lgpl2Plus) maintained by nobody
 - elfutils-0.190 (gpl2Only, lgpl3Plus, gpl3Plus) maintained by Eelco Dolstra, Ryan Burns
 - libwebp-1.3.2 (bsd3) maintained by Andreas Schrägle
 - libXi-1.8.1 (no license) maintained by nobody
 - gobject-introspection-1.78.1 (gpl2, lgpl2) maintained by Bobby Rong, Tor Hedin Brønner, Jan Tojnar, Daniel Șerbănescu, Maxine Aubrey, Jason O'Conal, Artturi N
 - json-glib-1.8.0 (lgpl21Plus) maintained by Bobby Rong, Tor Hedin Brønner, Jan Tojnar, Daniel Șerbănescu, Maxine Aubrey
 - xz-5.4.5 (gpl2Plus, lgpl21Plus) maintained by Sander van der Burg
 - tcb-1.2 (bsd3) maintained by Yurii Izorkin
 - pcre2-10.42 (bsd3) maintained by Thomas Tuegel
 - kexec-tools-2.0.26 (gpl2) maintained by nobody
 - kmod-31 (lgpl21Plus, gpl2Plus) maintained by Artturi N
 - libunwind-1.6.2 (mit) maintained by Orivej Desh
 - perl-5.38.2 (artistic1) maintained by Eelco Dolstra
 - libseccomp-2.5.5 (lgpl21Only) maintained by Austin Seipp
 - perl5.38.2-Encode-Locale-1.05 (artistic1, gpl1Plus) maintained by nobody
 - perl5.38.2-Test-RequiresInternet-0.05 (artistic1, gpl1Plus) maintained by nobody
 - ncurses-6.4 (mit) maintained by nobody
 - zstd-1.5.5 (bsd3) maintained by Orivej Desh
 - curl-8.4.0 (curl) maintained by Jason O'Conal
 - perl5.38.2-HTTP-Negotiate-6.01 (artistic1, gpl1Plus) maintained by nobody
 - perl5.38.2-libwww-perl-6.72 (artistic1, gpl1Plus) maintained by nobody
 - systemd-254.6 (lgpl21Plus) maintained by Florian Klink, Finn Behrens
 - popt-1.19 (mit) maintained by Alyssa Ross
 - kmod-31 (lgpl21Plus, gpl2Plus) maintained by Artturi N
 - libXinerama-1.1.5 (no license) maintained by nobody
 - libgcrypt-1.10.3 (lgpl2Plus) maintained by Rahul Gopinath
 - acl-2.3.1 (gpl2Plus) maintained by nobody
 - libtasn1-4.19.0 (lgpl2Plus) maintained by nobody
 - perl5.38.2-HTML-Tagset-3.20 (artistic1, gpl1Plus) maintained by nobody
 - pcsclite-2.0.1 (bsd3) maintained by Anthony Roussel
 - libtiff-4.6.0 (libtiff) maintained by nobody
 - bzip2-1.0.8 (bsdOriginal) maintained by Jörg Thalheim
 - libbsd-unstable-2023-04-29 (beerware, bsd2, bsd3, bsdOriginal, isc, mit) maintained by Matthew Bauer
 - libkrb5-1.21.2 (mit) maintained by nobody
 - iso-codes-4.15.0 (lgpl21) maintained by nobody
 - fontconfig-2.14.2 (bsd2) maintained by Jan Tojnar
 - gzip-1.13 (gpl3Plus) maintained by nobody
 - linux-pam-1.5.2 (bsd3) maintained by nobody
 - libjpeg-turbo-2.1.5.1 (ijg) maintained by Vladimír Čunát, Cole Mickens, Kevin Amado
 - perl5.38.2-URI-5.21 (artistic1, gpl1Plus) maintained by nobody
 - dav1d-1.2.1 (bsd2) maintained by Michael Weiss
 - perl5.38.2-LWP-MediaTypes-6.04 (artistic1, gpl1Plus) maintained by nobody
 - libXau-1.0.11 (no license) maintained by nobody
```

## Nix profiles

### Switch to previous system profile

https://tldr.inbrowser.app/pages/linux/nixos-rebuild

```shell
sudo nixos-rebuild switch --rollback boot
sudo reboot
```

### List system profiles

```shell
sudo nix-env --list-generations --profile /nix/var/nix/profiles/system
```
```console
...
 282   2024-11-10 12:53:25   
 283   2024-11-11 10:45:46   (current)
```

```shell
ls -l /nix/var/nix/profiles/
```
```console
lrwxrwxrwx 1 root root 43 Dez 26  2023 default -> /nix/var/nix/profiles/per-user/root/profile
drwxr-xr-x 1 root root 16 Aug 15  2023 per-user
lrwxrwxrwx 1 root root 15 Nov 11 10:45 system -> system-283-link
lrwxrwxrwx 1 root root 77 Nov 10 12:53 system-282-link -> /nix/store/jb5krdbbylwwgvxiadiv6fxja2zgc4h3-nixos-system-yodaTab-24.05pre-git
lrwxrwxrwx 1 root root 77 Nov 11 10:45 system-283-link -> /nix/store/jf7ml8jzxrmg9djhfr8szq2f19hxysn5-nixos-system-yodaTab-24.05pre-git
```

The currently running system. This is the currently active generation. By comparing the store path with the above output, we see that it matches generation 429.

```shell
ls -l /run/current-system
```
```console
lrwxrwxrwx 1 root root 77 Nov 11 10:46 /run/current-system -> /nix/store/jf7ml8jzxrmg9djhfr8szq2f19hxysn5-nixos-system-yodaTab-24.05pre-git
```

### Deleting generations - Keep most recent X system profiles

https://nix.dev/manual/nix/2.18/command-ref/nix-env/delete-generations

> Periodically deleting old generations is important to make garbage collection effective. The is because profiles are also garbage collection roots.

A NixOS config example is given in [nix-gc.nix](modules/nix-gc.nix).

```shell
sudo nix-env --delete-generations +7 --profile /nix/var/nix/profiles/system
```

After deleting some generations, it is still necessary to collect garbage in order to free up your system. See below.

### Garbage collection - Delete unreachable store objects

https://nix.dev/manual/nix/2.18/command-ref/nix-collect-garbage

> `nix-collect-garbage` deletes all unreachable store objects in the Nix store to clean up your system.

* https://nixos.org/manual/nix/stable/package-management/garbage-collection.html
* https://discourse.nixos.org/t/why-doesnt-nix-collect-garbage-remove-old-generations-from-efi-menu/17592/4

First delete unreachable store objects:

```shell
# Delete unreachable store objects
sudo nix-collect-garbage

# Deletes all except the currently active generation prior to deleting unreachable store objects
#sudo nix-collect-garbage --delete-old
# Deletes all generations older than 14d prior to deleting unreachable store objects
#sudo nix-collect-garbage --delete-older-than 14d
```

Then remove leftover EFI entries of deleted generations:

```shell
sudo /run/current-system/bin/switch-to-configuration boot
```

### List installed packages

https://nix.dev/manual/nix/2.23/command-ref/nix-store

Command explanation:
- `--query`: Display information about store paths.
- `--requisites`: Prints out the closure of the store path paths.
- Closure:
  - The closure of a store path is the set of store paths that are directly or indirectly “reachable” from that store path; that is, it’s the closure of the path under the references relation. For a package, the closure of its derivation is equivalent to the build-time dependencies, while the closure of its output path is equivalent to its runtime dependencies. For correct deployment it is necessary to deploy whole closures, since otherwise at runtime files could be missing. The command nix-store --query --requisites prints out closures of store paths.
  - As an example, if the store object at path P contains a reference to a store object at path Q, then Q is in the closure of P. Further, if Q references R then R is also in the closure of P.

```shell
nix-store --query --requisites /run/current-system | grep cpupower
#=> /nix/store/2mnk7jknv47a5ja17i7gwfgmyqng0jbn-cpupower-6.12.10
```

Not sure if this differs from (https://www.reddit.com/r/NixOS/comments/fsummx/comment/fm3xken/):

```shell
nix-store --query --requisites /run/current-system/sw | grep cpupower
#=> /nix/store/2mnk7jknv47a5ja17i7gwfgmyqng0jbn-cpupower-6.12.10
```

Alternative:

- Include [package-list.nix](modules/package-list.nix) in your NixOS config, then a file with this content will be created:

```console
/nix/store/xqvjf11c3kkg6i2zmcv9hdxl6547p1zn-nixpkgs-src/nixos/modules/config/fonts/fontdir.nix
  /nix/store/2afpklvkf7xcw2f9kghpza4vfdgiphjj-X11-fonts

/nix/store/xqvjf11c3kkg6i2zmcv9hdxl6547p1zn-nixpkgs-src/nixos/modules/config/fonts/fontconfig.nix
  /nix/store/c1alidglhx0as1n7mqf1a0cp4w9pdpy1-fontconfig-2.15.0-bin

/nix/store/xqvjf11c3kkg6i2zmcv9hdxl6547p1zn-nixpkgs-src/nixos/modules/config/console.nix
  /nix/store/a0fbsn0xx6c1zviv2y24s2ryy2jdj6k0-kbd-2.6.4
```

### why-depends: Why is a package installed

Usage of `why-depends`: https://github.com/tldr-pages/tldr/blob/f952fc71c2587fa13207aee278eb8795af913438/pages/common/nix3-why-depends.md

Show why the currently running NixOS system requires a certain store path.

- Example: Why is one store path required.

```shell
nix --extra-experimental-features flakes --extra-experimental-features nix-command why-depends /run/current-system /nix/store/2mnk7jknv47a5ja17i7gwfgmyqng0jbn-cpupower-6.12.10
```
```console
/nix/store/qskanrhcqj6nirzv7v04j0im727yjxh3-nixos-system-yodaTab-24.11pre-git
└───/nix/store/r3qqxybh1g6kg653n04a51m26qw84hxv-system-path
    └───/nix/store/2mnk7jknv47a5ja17i7gwfgmyqng0jbn-cpupower-6.12.10
```

- Example: Why are any of the `ffmpeg-headless` store paths currently required?

```shell
for i in /nix/store/*ffmpeg-headless-*; do
  env PAGER=cat nix --extra-experimental-features flakes --extra-experimental-features nix-command why-depends /run/current-system "$i" 2>/dev/null
done;
```
```console
/nix/store/k7c7576sz868gzjci1z6l6nzmdnpd6xr-nixos-system-yodaTux-23.11pre-git
└───/nix/store/b9mbk3jvazblxfma5p2yvc9xlmvrqxx7-etc
    └───/nix/store/snva91gl7hlm0fsf5mg5k0prv8mwnhcv-pipewire-1.0.1
        └───/nix/store/jqlvhb8jfz43vkl14wsm88h6csmx8aia-ffmpeg-headless-6.0-lib
/nix/store/k7c7576sz868gzjci1z6l6nzmdnpd6xr-nixos-system-yodaTux-23.11pre-git
└───/nix/store/b9mbk3jvazblxfma5p2yvc9xlmvrqxx7-etc
    └───/nix/store/nhypp8f5h0xv9ar9wzbp12hzyg1vah1a-user-environment
        └───/nix/store/0df15gc1a4s98n961vdd2j1pkkckn901-resources-1.3.0
            └───/nix/store/f61vlw8ampb5nh25kvs9p7rbi3cclcr4-gtk4-4.12.5
                └───/nix/store/5r52pj0fj3b06r0qgglasfmqmsfh315q-gst-plugins-bad-1.22.9
                    └───/nix/store/dsdfn1k9hnxzdwvzirx2smfinziqc8bz-openal-soft-1.23.1
                        └───/nix/store/ci4z4i38d7akpi5fqcdr2nvd1sr30l3i-pipewire-1.0.3
                            └───/nix/store/rpnsg493xz3fjhfrlc3ifz2ln65kmi8q-ffmpeg-headless-6.1-lib
...
```

### Compare two system profiles

Get latest system profile. This is the profile (usually) being active after booting the system:

```shell
ls -1 /nix/var/nix/profiles/ | sort -t'-' -n -k2 | tail -n 1
#=> 120
```

Compare current with previous profile:

```shell
# https://discourse.nixos.org/t/how-to-know-what-nixpkgs-changes-affect-me/18142/6
prev="$(ls -r /nix/var/nix/profiles/ | grep -E 'system\-' | sed -n '2 p')"
curr=/nix/var/nix/profiles/system
nix --extra-experimental-features nix-command store diff-closures /nix/var/nix/profiles/"${prev}" "${curr}"
```

```shell
# https://stackoverflow.com/a/36641298
prev="$(ls -1 /nix/var/nix/profiles/ | sort -t'-' -n -k2 | tail -n 2 | head -n 1)"
curr="$(ls -1 /nix/var/nix/profiles/ | sort -t'-' -n -k2 | tail -n 1)"
nix --extra-experimental-features nix-command store diff-closures /nix/var/nix/profiles/"${prev}" /nix/var/nix/profiles/"${curr}"
```

Compare two arbitrary system profiles:

```shell
nix --extra-experimental-features nix-command store diff-closures /nix/var/nix/profiles/system-110-link /nix/var/nix/profiles/system-116-link
```
```
cpupower: 6.1.47 → 6.1.51
element-desktop: 1.11.38 → 1.11.40, +2218.9 KiB
element-web: 1.11.38 → 1.11.40, -73.1 KiB
exempi: 2.6.3 → 2.6.4
firefox: 116.0.3 → 117.0
firefox-unwrapped: 116.0.3 → 117.0, -292.6 KiB
gnome-shell-extension-openweather: ∅ → 121, +590.5 KiB
hm_fontconfigconf.d10hmfonts.conf: ∅ → ε
initrd: ∅ → ε
initrd-linux: 6.1.47 → 6.1.51
libcap: 2.68 → 2.69
linux: 6.1.47, 6.1.47-modules → 6.1.51, 6.1.51-modules, -11.8 KiB
meld: ∅ → 3.22.0, +3858.5 KiB
net-snmp: 5.9.3 → 5.9.4
nixos-system-yodaTab: 23.05.3085.2ab91c8d65c0 → 23.05.3242.da5adce0ffaf
openjdk: +19.5 KiB
python3.10-pygobject: +27.0 KiB
stage: ∅ → 1-init.sh, +29.5 KiB
tor-browser-bundle-bin: 12.5.2 → 12.5.3, +18.1 KiB
user: +2885.0 KiB
```

## NixOS configuration debugging

* https://nixos.wiki/wiki/Nix_command/repl

Evaluating parts of the configuration.

First, start `nix repl`:

```shell
nix repl --file '<nixpkgs/nixos>' -I nixos-config=hosts/$(hostname)/configuration.nix
```

Example: `config.home-manager`

```shell
config.home-manager.
# Press `TAB`
#=> config.home-manager.backupFileExtension  config.home-manager.useUserPackages
#=> config.home-manager.extraSpecialArgs     config.home-manager.users
#=> config.home-manager.sharedModules        config.home-manager.verbose
#=> config.home-manager.useGlobalPkgs
```

Example: The `home` variable:

```shell
config.home-manager.users.yoda.home
```

Example: The value of one config option

```shell
# The following option is set to `"${config.xdg.dataHome}/.histfile";`
# where `config` is the Home Manager configuration.

config.home-manager.users.yoda.programs.zsh.history.path
#=> "/home/yoda/.local/share/.histfile"
```

## Show Nix configuration

* https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-show-config.html

```shell
nix --extra-experimental-features nix-command show-config
```

## Evaluate NixOS configuration to JSON

See also section "NixOS Configuration Debugging"!

* https://discourse.nixos.org/t/can-i-run-nix-instantiate-eval-strict-on-my-configuration-nix/7105/4

This evaluates `configuration.nix` (single module):

```shell
NIXPKGS_ALLOW_UNFREE=1 nix-instantiate --strict --json --eval -E '
import ./hosts/yodaTab/configuration.nix  {
  config = {};
  pkgs = import <nixpkgs> {};
  lib = import <nixpkgs/lib>;
}
' > evaluated-config.json
```

Then open `evaluated-config.json`.

## Evaluate expressions in the context of a NixOS configuration managed with Colmena

https://colmena.cli.rs/unstable/reference/cli.html#colmena-eval

Either specify a file containing the expression or add it as argument with `-E`.

```shell
colmena eval -E '{ nodes, lib, pkgs, ... }: nodes.yodaTux.config.networking.hostName'
```

```shell
nix-shell -p jq
colmena eval -E '{ nodes, lib, pkgs, ... }: nodes.yodaTux.config.environment.systemPackages' | jq
```

```shell
colmena eval -E '{ nodes, lib, pkgs, ... }: pkgs.linux' 
#=> "/nix/store/bmyh7a4j9xim7xxc5x1qk1qvlb2y7186-linux-6.6.48"
```

```shell
colmena eval -E '{ nodes, lib, pkgs, ... }: pkgs.linuxPackages.kernel'  
#=> "/nix/store/bmyh7a4j9xim7xxc5x1qk1qvlb2y7186-linux-6.6.48"
colmena eval -E '{ nodes, lib, pkgs, ... }: pkgs.linuxPackages_latest.kernel'
#=> "/nix/store/n0csng9aw5nhpll1m5rbvvxkkj2j63px-linux-6.10.7"
```

Lists and strings will be printed. To inspect an attribute set, add `pkgs.lib.attrNames`.

```shell
colmena eval -E '{ nodes, lib, pkgs, ... }: pkgs.lib.attrNames nodes.yodaTux.pkgs.rust-bin.stable.latest.default'
#=> [...,"type","userHook","version"]
```

## Evaluate expressions

* https://discourse.nixos.org/t/eval-nix-expression-from-the-command-line/8993/6

```shell
nix-instantiate --eval -E 'with import <nixpkgs> { }; vscode.version'
#=> "1.78.2"
```

Shell wrapper:

```shell
nix-eval() { nix-instantiate --eval -E "with import <nixpkgs> {}; ${*}"; }
```

Examples:

```shell
nix-eval 'vscode.version'
#=> "1.78.2"
nix-eval 'lib.forEach [ 1 2 ] (x: toString x)'
#=> [ "1" "2" ]
nix-eval 'lib.head [1 2]'
#=> 1
nix-eval 'lib.head (
  lib.forEach [ 1 2 ] (x: toString x)
)'
#=> "1"
nix-eval 'lib.head (
  lib.forEach [ {a=1;} {a=2;} ] (x: x.a)
)'
#=> 1
nix-eval 'lib.attrsets.mergeAttrsList [{a=1;} {b=2;}]'
#=> { a = 1; b = 2; }
nix-eval '{ a=1; }.b or 2'
#=> 2
nix-eval '{ a=false; }.a or true'
#=> false
nix-eval '{ a=1; }?a'
#=> true
nix-eval 'with lib.strings; concatMapStrings (x: " -a " + x + " -i 600") ["sda" "sdc"]'
#=> " -a sda -i 600 -a sdc -i 600"
```

## Escape strings

* https://nixos.org/manual/nix/stable/language/values

Double-quoted strings (e.g. `"foo bar"`):
```
"  -> \"
\  -> \\
${ -> \${
```

Indented strings (e.g. `''foo bar''`):
* `${` -> `''${`
* `''` -> `'''`

URIs can be written without quotes (e.g. `http://example.org/foo.bar`).

## Run AppImages

* https://nixos.wiki/wiki/Appimage

```shell
# Note how your shell prefix changes.
nix-shell -p appimage-run
```
```shell
# Inside the shell, you can run an AppImage:
appimage-run ~/Downloads/ubports-installer_0.10.0_linux_x86_64.AppImage
```

See the [binfmt option](https://nixos.org/manual/nixos/stable/options#opt-programs.appimage.binfmt) to e.g. run AppImages of other processor architectures.

## Audio troubleshooting - Realtek ALC898 Audio Codec on ASRock Z77 Extreme 4

TODO: I couldn't get the onboard audio to work.

- https://discourse.nixos.org/t/fixing-audio-on-asus-strix-scar-17-g733qs/12687
- https://bbs.archlinux.org/viewtopic.php?id=147242
- https://en.opensuse.org/SDB:Audio_troubleshooting#Script_to_run_to_obtain_detailed_information
- https://nixos.wiki/wiki/ALSA#Other_hardware_specific_problems
- https://bbs.archlinux.org/viewtopic.php?pid=1452128#p1452128

`aplay -L`
```console
null
    Discard all samples (playback) or generate zero samples (capture)
pipewire
    PipeWire Sound Server
default
    Default ALSA Output (currently PipeWire Media Server)
hdmi:CARD=HDMI,DEV=0
    HDA ATI HDMI, HDMI 0 *
    HDMI Audio Output
hdmi:CARD=HDMI,DEV=1
    HDA ATI HDMI, HDMI 1
    HDMI Audio Output
hdmi:CARD=HDMI,DEV=2
    HDA ATI HDMI, HDMI 2
    HDMI Audio Output
hdmi:CARD=HDMI,DEV=3
    HDA ATI HDMI, HDMI 3
    HDMI Audio Output
hdmi:CARD=HDMI,DEV=4
    HDA ATI HDMI, HDMI 4
    HDMI Audio Output
hdmi:CARD=HDMI,DEV=5
    HDA ATI HDMI, HDMI 5
    HDMI Audio Output
```

`cat /proc/asound/cards`
```console
 0 [HDMI           ]: HDA-Intel - HDA ATI HDMI
                      HDA ATI HDMI at 0xf7b60000 irq 40
```

`lspci -vnn | grep -A1 -i audio`
```console
00:1b.0 Audio device [0403]: Intel Corporation 7 Series/C216 Chipset Family High Definition Audio Controller [8086:1e20] (rev 04)
        Subsystem: ASRock Incorporation Z77 Extreme4 motherboard [1849:1898]
--
01:00.1 Audio device [0403]: Advanced Micro Devices, Inc. [AMD/ATI] Tahiti HDMI Audio [Radeon HD 7870 XT / 7950/7970] [1002:aaa0]
        Subsystem: Advanced Micro Devices, Inc. [AMD/ATI] Tahiti HDMI Audio [Radeon HD 7870 XT / 7950/7970] [1002:aaa0]
        Flags: bus master, fast devsel, latency 0, IRQ 40
```

`sudo lspci -vnn`
```console
00:1b.0 Audio device [0403]: Intel Corporation 7 Series/C216 Chipset Family High Definition Audio Controller [8086:1e20] (rev 04)
        Subsystem: ASRock Incorporation Z77 Extreme4 motherboard [1849:1898]
        Flags: fast devsel, IRQ 22
        Memory at f7c10000 (64-bit, non-prefetchable) [size=16K]
        Capabilities: [50] Power Management version 2
        Capabilities: [60] MSI: Enable- Count=1/1 Maskable- 64bit+
        Capabilities: [70] Express Root Complex Integrated Endpoint, MSI 00
        Capabilities: [100] Virtual Channel
        Capabilities: [130] Root Complex Link
        Kernel modules: snd_hda_intel
```

## Graphic drivers

Usually most of this should work out of the box on NixOS.

Vulkan:
- Verification:
  - If `vulkaninfo` returns information about your GPU, Vulkan is working. https://wiki.archlinux.org/title/Vulkan#Verification
    - `nix-shell -p vulkan-tools --run vulkaninfo`
  - Run `vkcube` (X11) or `vkcube-wayland` (Wayland). It should view a spinning 3D cube and output e.g. `Selected GPU 0: AMD Radeon Graphics (RADV RENOIR)`
    - `nix-shell -p vulkan-tools --run vkcube-wayland`

OpenGL:
- Verification: https://wiki.archlinux.org/title/OpenGL#Verification
  - `eglinfo -B` should not return `eglInitialize failed`
    - `nix-shell -p glxinfo --run 'eglinfo -B'`
  - `eglgears_x11` and `eglgears_wayland` -> ![eglgears.png](assets/doc/eglgears.png)
    - `nix-shell -p mesa-demos --run eglgears_wayland`

Video acceleration:
- VA-API
  - Video Acceleration API (VA-API). Provides both hardware accelerated video encoding and decoding.
  - Verifying: `vainfo` -> E.g. `Driver version: Mesa Gallium driver 23.1.9 for AMD Radeon Graphics`. https://wiki.archlinux.org/title/Hardware_video_acceleration#Verifying_VA-API
    - `nix-shell -p libva-utils --run vainfo`
  - Driver comparison chart. https://wiki.archlinux.org/title/Hardware_video_acceleration#VA-API_drivers
    - With `libva-mesa-driver` on "Radeon RX 7900 and higher/newer" a codec for encoding AV1 8 and 10 bit is available.
- VDPAU
  - Video Decode and Presentation API for Unix (VDPAU). Offload portions of the video decoding process and video post-processing to the GPU video-hardware.
  - Verifying: `vdpauinfo`. https://wiki.archlinux.org/title/Hardware_video_acceleration#Verifying_VDPAU
    - `nix-shell -p vdpauinfo --run vdpauinfo`

GPGPU (General-purpose computing on graphics processing units):
  - OpenCL
    - Verification using `clinfo`
      - `nix-shell -p clinfo --run 'clinfo -l'`
        - Should produce non-empty output, e.g. `Platform #0: AMD Accelerated Parallel Processing`
      - `nix-shell -p clinfo --run clinfo`
        - This output is more verbose.
        - `Number of platforms` should be >= 1

Verify video driver in use:
- `lspci -k | grep -EA3 'VGA|3D|Display'`. Example: `Kernel driver in use: amdgpu`
  - `nix-shell -p pciutils --run 'lspci -k | grep -EA3 "VGA|3D|Display"'`

Verification in general:
- Encode a video or play a game and watch AMD GPU usage with `radeontop`.
  - `nix-shell -p radeontop --run radeontop`

Configuration example to disable integrated GUP: See [./hosts/yodaGaming/configuration.nix](./hosts/yodaGaming/configuration.nix)

Configuration example for an AMD GPU (https://github.com/tolgaerok/nixos-kde/blob/main/core/gpu/amd/default.nix): See [./modules/gpu-amd.nix](./modules/gpu-amd.nix)

## XDG mimes, desktop files

Desktop files:
- `/run/current-system/sw/share/applications`
- `/etc/profiles/per-user/yoda/share/applications/`

Both above sub-paths are part of the `XDG_DATA_DIRS` variable:
- `echo $XDG_DATA_DIRS | grep /run/current-system/sw/share`
- `echo $XDG_DATA_DIRS | grep /etc/profiles/per-user/yoda/share`

List default apps and the associated handlers:

```shell
handlr list
```
```console
┌────────────────────────────────┬─────────────────────────────────────────┐
│ application/octet-stream       │ thunderbird.desktop                     │
│ ...                            │                                         │
│ x-scheme-handler/sgnl          │ signal-desktop.desktop                  │
└────────────────────────────────┴─────────────────────────────────────────┘
```

Set default handler for mime/extension:

```shell
handlr set text/html re.sonny.Junction.desktop
```

Open any URI with `handlr`:

```shell
handlr open https://wikipedia.org
```

Open any URI with `gio`, part of `glib`:

```shell
gio open https://wikipedia.org
```

- Note: `gio open` does not follow the XDG spec. https://discourse.nixos.org/t/configure-how-xdg-open-opens-html-files/6419/23

Further examples:

```shell
xdg-settings get default-web-browser
#=> re.sonny.Junction.desktop
xdg-mime query default x-scheme-handler/http and x-scheme-handler/https
#=> re.sonny.Junction.desktop
xdg-mime query default text/html
#=> firefox.desktop
```

## Additional resources

* Simple NixOS flake template for NixOS with HomeManager. https://github.com/Misterio77/nix-starter-configs#readme
* NixOS guide (development environment, gaming, etc). https://github.com/mikeroyal/NixOS-Guide#table-of-contents
* nix function cheatsheet: https://nix-cheatsheet.pixie.homes/
* Documenting the Journey of Learning and Mastering Nix. https://ianthehenry.com/posts/how-to-learn-nix/
* Nix language basics. https://nix.dev/tutorials/nix-language.html
* Nix data types. https://nixos.org/manual/nix/stable/language/values
* MkIfElse. https://discourse.nixos.org/t/mkif-vs-if-then/28521/4
* Nix language basics - a one-pager. https://github.com/tazjin/nix-1p#nix---a-one-pager

### Nix Pills

* https://nixos.org/guides/nix-pills/pr01

It provides a tutorial introduction into the Nix package manager and Nixpkgs package collection, in the form of short
chapters called 'pills'.

### Papers

Papers about Nix:

* The Purely Functional Software Deployment Model (2006). http://nixos.org/~eelco/pubs/phd-thesis.pdf, https://edolstra.github.io/pubs/phd-thesis.pdf, https://github.com/edolstra/edolstra.github.io/blob/master/pubs/phd-thesis.pdf
  * May 2023: Some insights from the thesis in short form. https://jonathanlorimer.dev/posts/nix-thesis.html
* NixOS: A Purely Functional Linux Distribution (2008): https://github.com/edolstra/edolstra.github.io/blob/master/pubs/nixos-icfp2008-final.pdf, https://github.com/edolstra/edolstra.github.io/blob/master/pubs/nixos-jfp-final.pdf
* Nix: A Safe and Policy-Free System for Software Deployment (2004): https://edolstra.github.io/pubs/nspfssd-lisa2004-final.pdf
* Prins, P., Suresh, J. and Dolstra, E., "Nix fixes dependency hell on all Linux distributions," [Archived](https://web.archive.org/web/20081226010942/http://www.linux.com/feature/155922) December 26, 2008, at the Wayback Machine linux.com, December 22, 2008