Codex intermittently segfaults when starting pytest in Conda env, while same repo/tests work in user terminal and Cursor

Resolved 💬 3 comments Opened Mar 14, 2026 by guido-h Closed Jul 2, 2026

💡 Likely answer: A maintainer (etraut-openai, contributor) responded on this thread — see the highlighted reply below.

Title: Codex intermittently segfaults when starting pytest in Conda env, while same repo/tests work in user terminal and Cursor

Product: Codex desktop app / Codex coding agent runner
Date/time: March 14, 2026, America/Los_Angeles
OS: macOS
Repo: /Users/guido/dev/cerbex/CBE_P

Issue:
Codex intermittently fails to validate unit tests in a Conda environment. In this repo, pytest startup sometimes exits with Segmentation fault: 11 under Codex, even when following the repo’s required Conda workflow exactly. The same commands work for the user in their own terminal and have also worked in some other Codex/Cursor sessions, so this appears intermittent and runner-specific.

Expected behavior:
Codex should be able to activate the existing Conda env and run pytest reliably, or at minimum fail with a normal Python/test error rather than a segfault.

Actual behavior:
Inside Codex, after:

cd /Users/guido/dev/cerbex/CBE_P
source /Users/guido/anaconda3/etc/profile.d/conda.sh
conda activate CBE_P
pytest tests/unit/api/test_hotel_websocket.py -q

pytest sometimes crashes immediately with:
Segmentation fault: 11

Additional observations:

python -c "import pytest; print(pytest.__version__)" succeeds in the same activated env.
python -m pytest --version can segfault under Codex.
The same repo and env work from the user’s terminal outside Codex.
Some Codex sessions succeed; others fail, so the issue appears intermittent.
We explicitly ruled out command drift:
no .venv
no poetry run pytest
no conda run
persistent PTY shell used
Repo docs were updated to standardize this flow, but the segfault still occurs in some Codex sessions.

Why this matters:
The agent can write tests but cannot always validate them, which makes unit-test tasks unreliable in Conda-based repos.

Artifacts available:

conversation transcript showing repeated segfaults in Codex
repo-local instructions used by the agent
exact commands above

View original on GitHub ↗

3 Comments

etraut-openai contributor · 5 months ago

Thanks for the bug report. I want to make sure I understand. The title seems to imply that codex is segfaulting, but when I read the description, it sounds like pytest is segfaulting. Can you clarify which it is and fix the title if it's pytest that's crashing?

jiamo · 5 months ago

In my env:
LC_ALL=C.UTF-8 python -m pytest will break
while codex has such ENV, claude doesn't has it.

jiamo · 5 months ago

I dug this down to a concrete root cause on macOS.

What I can reproduce reliably:

In Codex unified exec, child processes get LC_ALL=C.UTF-8
On my macOS Python env, LC_ALL=C.UTF-8 python -c "import readline" segfaults
env -u LC_ALL python -c "import readline" succeeds
pytest imports readline during startup, so python -m pytest --version and normal pytest runs can crash before collection

So the failure is not just “pytest is flaky in Codex”. The stronger root cause is that unified exec forces LC_ALL=C.UTF-8, and that locale value is not safe on macOS.

Suggested direction:

do not force LC_ALL in unified exec
inherit the user’s locale by default
if a UTF-8 fallback is still needed, only apply it when no locale vars are set, and avoid hardcoding C.UTF-8 on macOS

Workarounds I verified:

env -u LC_ALL python -m pytest ...
disabling unified exec / running locally outside unified exec

codex itself https://github.com/openai/codex/compare/main...jiamo:codex:fix/unified-exec-macos-locale?expand=1