path: root/_posts/2018-07-17-running-guix-on-nixos.md

---
title: Running Guix on NixOS
date: 2018-07-17
layout: post
lang: en
ref: running-guix-on-nixos
---
I wanted to run
Guix on a NixOS machine. Even though the Guix manual explains how to do it
[step by step][0], I needed a few extra ones to make it work properly.

[0]: https://www.gnu.org/software/guix/manual/en/html_node/Binary-Installation.html#Binary-Installation

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 [manual][1] already provides you with a ready to run (as root) command for
creating the build users:

[1]: https://www.gnu.org/software/guix/manual/en/html_node/Build-Environment-Setup.html#Build-Environment-Setup

```bash
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
```

However, In my personal NixOS I have disabled [`users.mutableUsers`][2], which
means that even if I run the above command it means that they'll be removed once
I rebuild my OS:

[2]: https://nixos.org/nixos/manual/index.html#sec-user-management

```shell
$ 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’
(...)
```

Instead of enabling `users.mutableUsers` I could add the Guix users by
adding them to my system configuration:

```nix
{ 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";
    };
  };
}
```

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 [`guix-daemon.service.in`][3] configuration to an equivalent Nix
expression

[3]: https://git.savannah.gnu.org/cgit/guix.git/tree/etc/guix-daemon.service.in?id=00c86a888488b16ce30634d3a3a9d871ed6734a2

```ini
# 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
```

This sample `systemd` configuration file became:

```nix
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" ];
};
```

There you go! After running `sudo nixos-rebuild switch` I could get Guix
up and running:

```bash
$ 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!
```

Some improvements to this approach are:

1.  looking into [NixOS modules][4] and trying to bundle everything together
    into a single logical unit;
2.  [build Guix from source][5] and share the Nix store and daemon with Guix.

Happy Guix/Nix hacking!

[4]: https://nixos.org/nixos/manual/index.html#sec-writing-modules
[5]: https://www.gnu.org/software/guix/manual/en/html_node/Requirements.html#Requirements