2025-05-28 Nix team meeting minutes #229

roberth · June 4, 2025, 10:04pm

Wednesday triage session

Attendees: @edolstra, @roberth, @ericson2314, @xokvidium, @fzakaria (briefly)

Triage

Test failure with SIGSYS when cross buidling to binary-compatible target · Issue #13042 · NixOS/nix · GitHub

Appears to be a problem with running 32-bit x86 on x86_64-linux. This should work, but is possibly host-dependent and seccomp may interfere.

The basic issue is that the code was written assuming cross

Assigned @Ericson2314

`nix-build --rebuild` does not work with remote builders · Issue #10451 · NixOS/nix · GitHub

github.com/NixOS/nix

`nix-build --rebuild` does not work with remote builders

opened 06:52AM - 10 Apr 24 UTC

Tristano8

bug remote build

**Describe the bug** `nix build` doesn't use a remote builder, even when pass…ed explicitly via `--builder`, unless explicitly telling it to ignore local builds. It seems like the nix scheduler thinks that it can build an `x86_64-linux` derivation locally, then at build time discovers that it cannot actually do that **Steps To Reproduce** 1. On a silicon Mac, set up a remote builder in `/etc/nix/nix.conf` for `x86_64-linux` eg: ``` builders = ssh://mybuilder x86_64-linux - 6 builders-use-substitutes = true ``` 3. Run `nix build -Lv --rebuild nixpkgs#legacyPackages.x86_64-linux.hello` 4. See the following error: ``` error: a 'x86_64-linux' with features {} is required to build '/nix/store/amplsdcav0g3qp9srkkfnqlkr8zc3sn8-hello-2.12.1.drv', but I am a 'x86_64-darwin' with features {apple-virt, benchmark, big-parallel, nixos-test} ``` 5. Repeat step 3 with `--max-jobs 0` 6. Observe no error **Expected behavior** The result from step 6 should occur without passing `--max-jobs` **`nix-env --version` output** nix-env (Nix) 2.18.1 **Additional context** This occurs on multiple silicon machines (M1 and M3) and across multiple nix versions (2.21.1 and 2.18.1 at least). Full error logs: [error-log.txt](https://github.com/NixOS/nix/files/14928546/error-log.txt) My `nix show-config`: ``` accept-flake-config = false access-tokens = <REDACTED> allow-dirty = true allow-import-from-derivation = true allow-symlinked-store = false allow-unsafe-native-code-during-evaluation = false allowed-impure-host-deps = /System/Library /bin/sh /dev /usr/lib allowed-uris = allowed-users = * auto-allocate-uids = false auto-optimise-store = false bash-prompt = bash-prompt-prefix = bash-prompt-suffix = build-hook = /nix/store/6zi5fqzn9n17wrk8r41rhdw4j7jqqsi3-nix-2.18.1/bin/nix __build-remote build-poll-interval = 5 build-users-group = nixbld builders = ssh://remote-builder x86_64-linux - 6 builders-use-substitutes = true commit-lockfile-summary = compress-build-log = true connect-timeout = 0 cores = 12 darwin-log-sandbox-violations = false diff-hook = download-attempts = 5 download-speed = 0 eval-cache = true experimental-features = flakes nix-command extra-platforms = aarch64-darwin fallback = false flake-registry = https://channels.nixos.org/flake-registry.json fsync-metadata = true gc-reserved-space = 8388608 hashed-mirrors = http-connections = 25 http2 = true id-count = 128 ignore-try = false impersonate-linux-26 = false keep-build-log = true keep-derivations = true keep-env-derivations = false keep-failed = false keep-going = false keep-outputs = false log-lines = 10 max-build-log-size = 0 max-free = 2147483648 max-jobs = 1 max-silent-time = 0 max-substitution-jobs = 16 min-free = 1073741824 min-free-check-interval = 5 nar-buffer-size = 33554432 narinfo-cache-negative-ttl = 3600 narinfo-cache-positive-ttl = 2592000 netrc-file = /etc/nix/netrc nix-path = /Users/hughdavidson/.nix-defexpr/channels nixpkgs=/nix/var/nix/profiles/per-user/root/channels/nixpkgs /nix/var/nix/profiles/per-user/root/channels plugin-files = post-build-hook = pre-build-hook = preallocate-contents = false print-missing = true pure-eval = true require-drop-supplementary-groups = false require-sigs = true restrict-eval = false run-diff-hook = false sandbox = false sandbox-fallback = true sandbox-paths = /System/Library/Frameworks /System/Library/PrivateFrameworks /bin/bash /bin/sh /private/tmp /private/var/tmp /usr/lib secret-key-files = show-trace = false ssl-cert-file = /nix/var/nix/profiles/default/etc/ssl/certs/ca-bundle.crt stalled-download-timeout = 300 start-id = 56930 store = auto substitute = true substituters = <REDACTED> sync-before-registering = false system = x86_64-darwin system-features = benchmark big-parallel nixos-test tarball-ttl = 3600 timeout = 0 trace-function-calls = false trace-verbose = false trusted-public-keys = <REDACTED> trusted-substituters = trusted-users = hughdavidson use-case-hack = true use-registries = true use-sqlite-wal = true use-xdg-base-directories = false user-agent-suffix = warn-dirty = true ```

Temporary build directories not cleaned up because they are not empty · Issue #5207 · NixOS/nix · GitHub

readdir might not support concurrent deletes well, and this might be fs-dependent

Assigned to @edolstra

GitHub · Where software is built

github.com/NixOS/nix

Unhelpful error message when a substituter is missing a dependency

opened 05:38PM - 05 Mar 25 UTC

lheckemann

bug store scheduling

## Describe the bug When trying to fetch the narinfo for a dependency from a su…bstituter fails (i.e. the substituter isn't upholding the store invariants), this isn't reported clearly. This was first observed with cachix (and doesn't occur reliably there -- maybe its sporadic 502s affect cache service as well?), but can also be reproduced with a synthetic test case. ## Steps To Reproduce ``` rm -rf /tmp/binarycache /tmp/store drv=$(nix-instantiate '<nixpkgs>' -A hello) out=$(nix-store -q --outputs $drv) nix build $drv^out nix copy $out --to file:///tmp/binarycache # remove a dependency of hello from the binary cache rm -v $(grep -lE '^StorePath: .*(glibc|iconv)' /tmp/binarycache/*.narinfo) nix-store --store /tmp/store --substituters file:///tmp/binarycache?trusted=1 -r $out --narinfo-cache-positive-ttl 1 --narinfo-cache-negative-ttl 1 ``` The final command will fail something like this: ``` this path will be fetched (0.05 MiB download, 0.22 MiB unpacked): /nix/store/crrf4bysvarqp0g9pyhcrj47689g4i5l-hello-2.12.1 don't know how to build these paths: /nix/store/nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36 error: build of '/nix/store/crrf4bysvarqp0g9pyhcrj47689g4i5l-hello-2.12.1' failed ``` If the drv is copied to the chroot store and realised instead of its output path, the behaviour combines somewhat oddly, claiming that it doesn't know how to build the dependency and yet starting to do so anyway: ``` $ nix-store --store /tmp --substituters file:///tmp/binarycache?trusted=1 -r /nix/store/7s3p1q56abzik34w93kw7jx37l37ycg8-hello-2.12.1.drv --narinfo-cache-positive-ttl 1 --narinfo-cache-negative-ttl 1 --no-fallback this path will be fetched (0.05 MiB download, 0.22 MiB unpacked): /nix/store/crrf4bysvarqp0g9pyhcrj47689g4i5l-hello-2.12.1 don't know how to build these paths: /nix/store/nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36 building '/nix/store/1crz16gbhsxjxkyp2zxjf5y7a224m4j7-bash52-033.drv'... building '/nix/store/0m4y3j4pnivlhhpr5yqdvlly86p93fwc-busybox.drv'... [...] ``` ## Expected behavior A warning when a path that's expected in a binary cache (based on the store invariant "all dependencies should be there"), ideally with details on how getting the narinfo failed. ## Metadata nix (Nix) 2.26.1 ## Additional context It might be possible to trigger the same kind of failure without breaking the "all dependencies are present" invariant if through a somewhat convoluted combination of GC operations: - The narinfo for the dependent (hello) is present in the client's narinfo cache - The narinfo for the dependency (glibc or iconv) is _not_ in the client's narinfo cache (glibc/iconv was already present on the client when the dependent was last queried) - The narinfo for the dependency is _not_ present in the binary cache due to a GC. ## Checklist - [x] checked [latest Nix manual] \([source]) - [x] checked [open bug issues and pull requests] for possible duplicates [latest Nix manual]: https://nixos.org/manual/nix/unstable/ [source]: https://github.com/NixOS/nix/tree/master/doc/manual/source [open bug issues and pull requests]: https://github.com/NixOS/nix/labels/bug --- Add :+1: to [issues you find important](https://github.com/NixOS/nix/issues?q=is%3Aissue+is%3Aopen+sort%3Areactions-%2B1-desc).

Store `StructuredAttrs` directly in `Derivation` by Ericson2314 · Pull Request #13263 · NixOS/nix · GitHub

github.com/NixOS/nix

Comment by Ericson2314 - Store `StructuredAttrs` directly in `Derivation`

master ← structured-attrs-in-drv

Notes from today's Nix team meeting: - What about perf of parsing the structu…red attrs eagerly? - @mic92 can check, perhaps - What about derivations that no longer parse during GC? This branch in https://github.com/NixOS/nix/blob/20226c85bcb141b02dcf87dd8fcf16df0dc85a2b/src/libstore/gc.cc#L754-L760 does parse derivations, to see if they point to outputs we should keep. We should recover if we fail to parse a derivation, and have a test for this. We also need to decide what we want to do in that case: delete or keep the derivation that doesn't parse? - @edolstra what are the use-cases / ultimate purpose you have for doing this? @ericson2314: Sure - Better derivation JSON format (or other new formats): That is useful for #8602 and dynamic derivations - Maybe better on-disk format too For input-addressed outputs, ATerm has to stick around forever at least as part of the path calculation. But for the newer experimental derivations types we have the opportunity to do a clean break.

Get rid of `addWantedOutputs` by Ericson2314 · Pull Request #13240 · NixOS/nix · GitHub

Ran out of time to review, but @ericson2314 added much more API docs after he found himself writing too much.