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content/posts/nixos-build-issues.md

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+---
+title: "Nixos Build Issues"
+date: 2025-09-28T20:06:51-05:00
+draft: false
+---
+So I am doing a rebuild of my [NixOS](https://nixos.org) laptop in order to (supposedly) highly optimize the resulting
+binary code for my local host. Or, at least, all of the libraries written in C. So doing this
+was pretty straightforward. Before we can build the optimized code, we need to tell Nix that our
+system supports this as a feature. So the first thing I enabled in my configuration is:
+
+```nix
+nix.settings.system-features = [ "gccarch-x86-64-v3" ];
+```
+
+A quick `nixos-rebuild switch` has me up and going in a few moments, as all it needs to do is
+write a new `nix.conf` file.
+
+## Enabling the Optimized Build
+
+Now, enabling the optimized build in your system is pretty straightforward. All you need to do
+is configure the `nixpkgs.hostPlatform`. The key setting to enable in my flake looks like such:
+
+```nix
+nixpkgs.hostPlatform = {
+  system = "x86_64-linux";
+  gcc.arch = "x86-64-v3";
+};
+```
+
+Ostensibly you can do this as well if you are doing an `import nixpkgs { ... }` function somewhere,
+but setting the above in my Flake config file was all I needed.
+
+## Go Grab a Drink
+
+...and a nap, and the rest of the afternoon, and probably an overnight sleep. Because this, for me,
+on a daily driver laptop with Gnome took building more than 3300 packages. All the way up from a
+bootstrap of the systems. My laptop, admittedly, isn't the most powerful system around. It's an
+11th gen [Intel](https://www.intel.com) i7 mobile processor from [Framework](https://frame.work).
+The benchmarks for it are kinda weak. The [i7-1165G7](https://www.cpubenchmark.net/cpu.php?cpu=Intel+Core+i7-1165G7+%40+2.80GHz&id=3814)
+from those first generation Framework boards are great for day to day work, and it doesn't limit me
+from anything that I need to do (I'm a software engineer, but most of what I do on my personal system
+is writing little scripts and personal data tracking projects here and there and doing some VM
+development). The low power consumption is great.
+
+My point is, your mileage may vary. My home servers are much more potent systems and can probably get
+their builds done much more quickly if this proves out to be useful.
+
+## A Build Failure?!
+
+Rather than waltz straight into a `nixos-rebuild switch` with wild abandon, I strongly recommend that
+you trial the build process with a `nix build` or similar. At the very least you will want to do something
+along the lines of `--keep-going` flag so that the builds continue. I know that NixOS builds are intended
+to be reproducible. But that doesn't mean every single package in the build tree has completely figured
+out deterministic tests.
+
+For my purposes, I had a build failure somewhere in the middle of the bootstrapping process that
+required me to manually build a single package. For me, it was the `bmake` package that failed when it
+tried to run its unit tests. Proving that it was no fluke, it failed 3 more times in the midst of a
+full system build. But it passes when built in isolation.
+
+Since I was building a very specific version of `bmake` that included the architecture tuning,
+I couldn't just do a `nix build "nixpkgs#bmake"` to get it into my local store. However, and this
+only works with a flake configuration - you'll need slightly diffrent syntax if you aren't using flakes.
+You can still get the build of a very specific package to happen. In my case, with a laptop host named
+"exodus", I could do the following
+
+```console
+nix build ".#nixosConfigurations.exodus.pkgs.bmake"
+```
+
+This command build the exact version of the package that was going to be used on my system with the
+optimizations in place and allowed me to progress the rest of the build.
+
+This time, with the `--keep-going` flag in order to waste as little time as possible if there were
+future hiccups.