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`nix-shell` may explode in flight because `/tmp/env-vars` exist if you have no `$TMPDIR` set #940

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opened 2025-07-28 18:13:26 +00:00 by raito · 5 comments

raito commented

2025-07-28 18:13:26 +00:00

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Describe the bug

nixpkgs stdenv has a phase load-bearing which is to dump env-vars in the $NIX_BUILD_TOP, in case, this is not possible, this explodes.

This is ironic because dumpVars is meant as a debugging tool but can take down your shell.

Nixpkgs could be slightly more lenient here and warn if dumpVars failed without crashing your shell.

In the meantime, Lix could probably do something better at picking $NIX_BUILD_TOP.

Steps To Reproduce

touch /tmp/env-vars as root
Use an unprivileged user and TMPDIR="" nix-shell -p gcc
Get exit code 1 with no error message.

Expected behavior

Warnings, error messages, and maybe a better choice of $TMPDIR fallback?

`nix --version` output

Probably all Nix versions.

Additional context

Debugged with the help of @lheckemann

## Describe the bug nixpkgs stdenv has a phase load-bearing which is to dump `env-vars` in the `$NIX_BUILD_TOP`, in case, this is not possible, this explodes. This is ironic because `dumpVars` is meant as a debugging tool but can take down your shell. Nixpkgs could be slightly more lenient here and warn if dumpVars failed without crashing your shell. In the meantime, Lix could probably do something better at picking `$NIX_BUILD_TOP`. ## Steps To Reproduce 1. `touch /tmp/env-vars` as root 2. Use an unprivileged user and `TMPDIR="" nix-shell -p gcc` 3. Get exit code 1 with no error message. ## Expected behavior Warnings, error messages, and maybe a better choice of `$TMPDIR` fallback? ## `nix --version` output Probably all Nix versions. ## Additional context Debugged with the help of @lheckemann

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raito added the

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2025-07-28 18:13:26 +00:00

jade commented

2025-07-28 18:23:36 +00:00

Owner

Isn't this fixed in nix3-develop? I'm pretty sure the latter gives a unique tmpdir for each shell or so.

raito commented

2025-07-28 19:04:43 +00:00

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Owner

i don't use nix3-develop but that might be possibly the case

jade commented

2025-07-28 21:56:22 +00:00

Owner

lol yeah I'm just pointing out that you could probably steal the code that works

raito pinned this

2025-08-18 10:18:38 +00:00

teofilc commented

2025-08-24 19:54:09 +00:00

FWIW I think the nix develop code is quite buggy in its own right, for a long time it triggered https://github.com/NixOS/nix/issues/10753 because it put you in a tempdir with different permissions. But it would be good if the two (nix-shell and nix3-develop) were consistent.

FWIW I think the `nix develop` code is quite buggy in its own right, for a long time it triggered https://github.com/NixOS/nix/issues/10753 because it put you in a tempdir with different permissions. But it would be good if the two (nix-shell and nix3-develop) were consistent.

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lix-bot commented

2025-08-25 12:06:13 +00:00

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This issue was mentioned on Gerrit on the following CLs:

commit message in cl/4090 ("legacy/nix-build: create various temporary directories into a known tempdir")

This issue was mentioned on Gerrit on the following CLs: * commit message in [cl/4090](https://gerrit.lix.systems/c/lix/+/4090) ("legacy/nix-build: create various temporary directories into a known tempdir")

raito referenced this issue

2025-08-25 12:06:35 +00:00

Inconsistent behavior in tempdir manipulations between nix-shell and nix3-develop #978