# Nixos-install fails building hwdb.bin

**URL:** https://discourse.nixos.org/t/nixos-install-fails-building-hwdb-bin/69750
**Category:** Help
**Created:** [September 25, 2025, 1:53am UTC](https://discourse.nixos.org/t/nixos-install-fails-building-hwdb-bin/69750 "2025-09-25T01:53:51Z")
**Posts on this page:** 1
**Showing post:** 6

<div class="post-metadata">

### Author: ![bme](https://discourse.nixos.org/letter_avatar_proxy/v4/letter/b/d2c977/32.png) [@bme](https://discourse.nixos.org/u/bme)
#### Post date: [September 25, 2025, 3:47pm UTC](https://discourse.nixos.org/t/nixos-install-fails-building-hwdb-bin/69750/6 "2025-09-25T15:47:35Z")

</div>

Well in an attempt to make myself more informed and give a more complete answer I decided to deliberately break a build and run it with `nix-build -K` so I could show you it was under `/tmp` (I know this wouldn’t answer the installer question, but one thing at a time).

```auto
error: could not compile `XXX` (bin "XXX") due to 1 previous error; 4 warnings emitted
note: keeping build directory '/nix/var/nix/builds/nix-666327-2838463246/build'

```

So not `/tmp`.

```auto
~/src/work/xxx/xxx inline-pkgs +1 !1 ▼  impure 16:40:35
❯ ll /nix/var/nix/builds/nix-666327-2838463246/build
drwxr-xr-x - nixbld1 25 Sep 16:38 cargo-vendor-dir
.rw------- 8.0k nixbld1 25 Sep 16:38 env-vars
drwxr-xr-x - nixbld1 25 Sep 16:38 xxx
.rw------- 111 nixbld1 25 Sep 16:38 tmp.4I0df9OtRn

```

I am pretty confident `tmp.4I0df9OtRn` is the private builder tmp.

I had forgotten that [2.30](https://nix.dev/manual/nix/2.31/release-notes/rl-2.30.html) moves default build-dir because of [reasons](https://discourse.nixos.org/t/security-advisory-privilege-escalations-in-nix-lix-and-guix/66017). So ignore everything I said about builds in `tmpdir` it’s all out of date, and it happens in `/nix`. Which doesn’t answer the installer question.

EDIT: having spent 30 seconds reading the installer, the call to `nix-build` has an undocumented `--store` (afaict) option that uses the mount point, so I would assume builds happen under `/mnt/nix`.

---

_[View the full topic](https://discourse.nixos.org/t/nixos-install-fails-building-hwdb-bin/69750)._