Celery empty line printed to stderr (Fix)

The Fix

pip install celery==5.1.2

Based on closed celery/celery issue #6834 · PR/commit linked

Production note: This usually shows up under retries/timeouts. Treat it as a side-effect risk until you can verify behavior with a canary + real traffic.

Jump to Verify Open PR/Commit

@@ -223,6 +223,7 @@ def write(self, data):
             # Logger is logging back to this file, so stop recursing.
             return 0
+        data = data.rstrip('\n')
         if data and not self.closed:
             self._thread.recurse_protection = True

repro.py

from celery import Celery

app = Celery('tasks', broker='redis://localhost:6379/0')


@app.task
def f():
    print('hello hello world')

if __name__ == '__main__':
    f.apply_async()

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

fix.md

Option A — Upgrade to fixed release\npip install celery==5.1.2\nWhen NOT to use: This fix should not be used if preserving trailing newlines is required.\n\n

Why This Fix Works in Production

Trigger: - [] I have included all related issues and possible duplicate issues
Mechanism: Trailing newlines in log messages caused empty lines to be printed to stderr
Why the fix works: Fixes the issue of empty lines being printed in the log output by stripping trailing newlines from the log messages. (first fixed release: 5.1.2).

Production impact:

If left unfixed, retries/timeouts can trigger duplicate external side-effects (double charges, duplicate emails, repeated writes).

Why This Breaks in Prod

Trailing newlines in log messages caused empty lines to be printed to stderr
Production symptom (often without a traceback): - [] I have included all related issues and possible duplicate issues

Proof / Evidence

GitHub issue: #6834
Fix PR: https://github.com/celery/celery/pull/6838
First fixed release: 5.1.2
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.75
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.64

Discussion

High-signal excerpts from the issue thread (symptoms, repros, edge-cases).

Jump to Sources Open on GitHub

“Hey @theendlessriver13 :wave:, Thank you for opening an issue”

@open-collective-bot · 2021-06-30 · source

Failure Signature (Search String)

- [] I have included all related issues and possible duplicate issues
or possible duplicates to this issue as requested by the checklist above.

Copy-friendly signature

signature.txt

Failure Signature
-----------------
- [] I have included all related issues and possible duplicate issues
or possible duplicates to this issue as requested by the checklist above.

Error Message

Signature-only (no traceback captured)

error.txt

Error Message
-------------
- [] I have included all related issues and possible duplicate issues
or possible duplicates to this issue as requested by the checklist above.

Minimal Reproduction

repro.py

from celery import Celery

app = Celery('tasks', broker='redis://localhost:6379/0')


@app.task
def f():
    print('hello hello world')

if __name__ == '__main__':
    f.apply_async()

What Broke

Empty lines were appearing in the log output, cluttering the logs.

Why It Broke

Trailing newlines in log messages caused empty lines to be printed to stderr

Fix Options (Details)

Option A — Upgrade to fixed release Safe default (recommended)

pip install celery==5.1.2

When NOT to use: This fix should not be used if preserving trailing newlines is required.

Use when you can deploy the upstream fix. It is usually lower-risk than long-lived workarounds.

Fix reference: https://github.com/celery/celery/pull/6838

First fixed release: 5.1.2

Last verified: 2026-02-09. Validate in your environment.

When NOT to Use This Fix

This fix should not be used if preserving trailing newlines is required.

Verify Fix

verify

Re-run the minimal reproduction on your broken version, then apply the fix and re-run.

Did This Fix Work in Your Case?

Quick signal helps us prioritize which fixes to verify and improve.

Prevention

Capture the exact failing error string in logs and tests so you can reproduce via a minimal script.
Pin production dependencies and upgrade only with a reproducible test that hits the failing path.

Version Compatibility Table

Version	Status
5.1.2	Fixed

Related Issues

No related fixes found.

Cluster: celery:duplicates Celery hub Celery best practices All hubs All clusters

Related clusters: Configuration error Data consistency Duplicate processing

Sources

We don’t republish the full GitHub discussion text. Use the links above for context.