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