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+---
+title: Running Guix on NixOS
+date: 2018-07-17
+layout: post
+---
+I wanted to run
+Guix on a NixOS machine. Even though the Guix manual explains how to do
+it [step by
+step](https://www.gnu.org/software/guix/manual/en/html_node/Binary-Installation.html#Binary-Installation),
+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
+[manual](https://www.gnu.org/software/guix/manual/en/html_node/Build-Environment-Setup.html#Build-Environment-Setup)
+already provides you with a ready to run (as root) command for creating
+the build users:
+
+``` {.bash .numberLines startFrom=""}
+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`](https://nixos.org/nixos/manual/index.html#sec-user-management),
+which means that even if I run the above command it means that they\'ll
+be removed once I rebuild my OS:
+
+``` {.shell .numberLines startFrom=""}
+$ 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 .numberLines startFrom=""}
+{ 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`](https://git.savannah.gnu.org/cgit/guix.git/tree/etc/guix-daemon.service.in?id=00c86a888488b16ce30634d3a3a9d871ed6734a2)
+configuration to an equivalent Nix expression
+
+``` {.ini .numberLines startFrom=""}
+# 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 .numberLines startFrom=""}
+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 .numberLines startFrom=""}
+$ 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](https://nixos.org/nixos/manual/index.html#sec-writing-modules)
+    and trying to bundle everything together into a single logical unit;
+2.  [build Guix from
+    source](https://www.gnu.org/software/guix/manual/en/html_node/Requirements.html#Requirements)
+    and share the Nix store and daemon with Guix.
+
+Happy Guix/Nix hacking!