path: root/site/posts/2018-07-17-running-guix-on-nixos.org

---
title: Running Guix on NixOS
date: 2018-07-17
---
I wanted to run Guix on a NixOS machine. Even though the Guix manual explains how to do it [[https://www.gnu.org/software/guix/manual/en/html_node/Binary-Installation.html#Binary-Installation][step by step]], I needed a few extra ones to make it work properly.

I couldn't just install GuixSD because my wireless network card doesn't have any free/libre drivers (yet).
** Creating =guixbuilder= users
Guix requires you to create non-root users that will be used to perform the builds in the isolated environments.

The [[https://www.gnu.org/software/guix/manual/en/html_node/Build-Environment-Setup.html#Build-Environment-Setup][manual]] already provides you with a ready to run (as root) command for creating the build users:
#+BEGIN_SRC bash -n
groupadd --system guixbuild
for i in `seq -w 1 10`;
do
  useradd -g guixbuild -G guixbuild           \
          -d /var/empty -s `which nologin`    \
          -c "Guix build user $i" --system    \
          guixbuilder$i;
done
#+END_SRC
However, In my personal NixOS I have disabled [[https://nixos.org/nixos/manual/index.html#sec-user-management][=users.mutableUsers=]], which means that even if I run the above command it means that they'll be removed once I rebuild my OS:
#+BEGIN_SRC
$ sudo nixos-rebuild switch
(...)
removing user ‘guixbuilder7’
removing user ‘guixbuilder3’
removing user ‘guixbuilder10’
removing user ‘guixbuilder1’
removing user ‘guixbuilder6’
removing user ‘guixbuilder9’
removing user ‘guixbuilder4’
removing user ‘guixbuilder2’
removing user ‘guixbuilder8’
removing user ‘guixbuilder5’
(...)
#+END_SRC
Instead of enabling =users.mutableUsers= I could add the Guix users by adding them to my system configuration:
#+BEGIN_SRC nix -n
{ config, pkgs, ...}:

{

  # ... NixOS usual config ellided ...

  users = {
    mutableUsers = false;

    extraUsers =
      let
        andrehUser =  {
          andreh = {
            # my custom user config
          };
        };
        buildUser = (i:
          {
            "guixbuilder${i}" = {                   # guixbuilder$i
              group = "guixbuild";                  # -g guixbuild
              extraGroups = ["guixbuild"];          # -G guixbuild
              home = "/var/empty";                  # -d /var/empty
              shell = pkgs.nologin;                 # -s `which nologin`
              description = "Guix build user ${i}"; # -c "Guix buid user $i"
              isSystemUser = true;                  # --system
            };
          }
        );
      in
        # merge all users
        pkgs.lib.fold (str: acc: acc // buildUser str)
                      andrehUser
                      # for i in `seq -w 1 10`
                      (map (pkgs.lib.fixedWidthNumber 2) (builtins.genList (n: n+1) 10));

    extraGroups.guixbuild = {
      name = "guixbuild";
    };
  };
}
#+END_SRC
Here I used =fold= and the =//= operator to merge all of the configuration sets into a single =extraUsers= value.
** Creating the =systemd= service
One other thing missing was the =systemd= service.

First I couldn't just copy the =.service= file to =/etc= since in NixOS that folder isn't writable. But also I wanted the service to be better integrated with the OS.

That was a little easier than creating the users, all I had to do was translate the provided [[https://git.savannah.gnu.org/cgit/guix.git/tree/etc/guix-daemon.service.in?id=00c86a888488b16ce30634d3a3a9d871ed6734a2][=guix-daemon.service.in=]] configuration to an equivalent Nix expression
#+BEGIN_SRC ini -n
# This is a "service unit file" for the systemd init system to launch
# 'guix-daemon'.  Drop it in /etc/systemd/system or similar to have
# 'guix-daemon' automatically started.

[Unit]
Description=Build daemon for GNU Guix

[Service]
ExecStart=/var/guix/profiles/per-user/root/guix-profile/bin/guix-daemon --build-users-group=guixbuild
Environment=GUIX_LOCPATH=/root/.guix-profile/lib/locale
RemainAfterExit=yes
StandardOutput=syslog
StandardError=syslog

# See <https://lists.gnu.org/archive/html/guix-devel/2016-04/msg00608.html>.
# Some package builds (for example, go@1.8.1) may require even more than
# 1024 tasks.
TasksMax=8192

[Install]
WantedBy=multi-user.target
#+END_SRC
This sample =systemd= configuration file became:
#+BEGIN_SRC nix -n
guix-daemon = {
  enable = true;
  description = "Build daemon for GNU Guix";
  serviceConfig = {
    ExecStart = "/var/guix/profiles/per-user/root/guix-profile/bin/guix-daemon --build-users-group=guixbuild";
    Environment="GUIX_LOCPATH=/root/.guix-profile/lib/locale";
    RemainAfterExit="yes";
    StandardOutput="syslog";
    StandardError="syslog";
    TaskMax= "8192";
  };
  wantedBy = [ "multi-user.target" ];
};
#+END_SRC
There you go! After running =sudo nixos-rebuild switch= I could get Guix up and running:
#+BEGIN_SRC bash -n
$ guix package -i hello
The following package will be installed:
   hello        2.10    /gnu/store/bihfrh609gkxb9dp7n96wlpigiv3krfy-hello-2.10

substitute: updating substitutes from 'https://mirror.hydra.gnu.org'... 100.0%
The following derivations will be built:
   /gnu/store/nznmdn6inpwxnlkrasydmda4s2vsp9hg-profile.drv
   /gnu/store/vibqrvw4c8lacxjrkqyzqsdrmckv77kq-fonts-dir.drv
   /gnu/store/hi8alg7wi0wgfdi3rn8cpp37zhx8ykf3-info-dir.drv
   /gnu/store/cvkbp378cvfjikz7mjymhrimv7j12p0i-ca-certificate-bundle.drv
   /gnu/store/d62fvxymnp95rzahhmhf456bsf0xg1c6-manual-database.drv
Creating manual page database...
1 entries processed in 0.0 s
2 packages in profile
$ hello
Hello, world!
#+END_SRC
Some improvements to this approach are:
1. looking into [[https://nixos.org/nixos/manual/index.html#sec-writing-modules][NixOS modules]] and trying to bundle everything together into a single logical unit;
2. [[https://www.gnu.org/software/guix/manual/en/html_node/Requirements.html#Requirements][build Guix from source]] and share the Nix store and daemon with Guix.

Happy Guix/Nix hacking!