The Fix
pip install celery==4.4.0rc5
Based on closed celery/celery issue #4638 · PR/commit linked
Production note: Most teams hit this during upgrades or environment changes. Roll out with a canary and smoke critical endpoints (health, OpenAPI/docs) before 100%.
@@ -202,6 +202,10 @@ def remove_if_stale(self):
self.remove()
return True
+ except SystemError as exc:
+ print('Stale pidfile exists - Removing it.', file=sys.stderr)
+ self.remove()
try:
os.kill(pid, 0)
except OSError as exc: # os.error as exc:
if exc.errno == errno.ESRCH:
print('Stale pidfile exists - Removing it.', file=sys.stderr)
self.remove()
return True
Re-run the minimal reproduction on your broken version, then apply the fix and re-run.
Option A — Upgrade to fixed release\npip install celery==4.4.0rc5\nWhen NOT to use: Do not apply this fix if the application does not use pid files for process management.\n\n
Why This Fix Works in Production
- Trigger: celery beat v4.1.0 (latentcall) is starting.
- Mechanism: The OSError occurs when trying to kill a non-existent process due to a stale pid file
- Why the fix works: Fixed Issue #4638 by catching the exception thrown for Windows 10 devices with stale pid files. (first fixed release: 4.4.0rc5).
- If left unfixed, the same config can fail only in production (env differences), causing startup failures or partial feature outages.
Why This Breaks in Prod
- The OSError occurs when trying to kill a non-existent process due to a stale pid file
- Surfaces as: celery beat v4.1.0 (latentcall) is starting.
Proof / Evidence
- GitHub issue: #4638
- Fix PR: https://github.com/celery/celery/pull/4892
- First fixed release: 4.4.0rc5
- Reproduced locally: No (not executed)
- Last verified: 2026-02-09
- Confidence: 0.85
- Did this fix it?: Yes (upstream fix exists)
- Own content ratio: 0.61
Discussion
High-signal excerpts from the issue thread (symptoms, repros, edge-cases).
“This error occurs from: celery/platforms.py:199 (remove_if_stale) It can be fixed by catching SystemError and wiping the pidfile, e.g: but Im not entirely sure how this…”
Failure Signature (Search String)
- celery beat v4.1.0 (latentcall) is starting.
Error Message
Stack trace
Error Message
-------------
celery beat v4.1.0 (latentcall) is starting.
OSError: [WinError 87] The parameter is incorrect
...
SystemError: <class 'OSError'> returned a result with an error set
Minimal Reproduction
try:
os.kill(pid, 0)
except OSError as exc: # os.error as exc:
if exc.errno == errno.ESRCH:
print('Stale pidfile exists - Removing it.', file=sys.stderr)
self.remove()
return True
What Broke
Celery beat fails to start while the worker continues to run, causing scheduling issues.
Why It Broke
The OSError occurs when trying to kill a non-existent process due to a stale pid file
Fix Options (Details)
Option A — Upgrade to fixed release Safe default (recommended)
pip install celery==4.4.0rc5
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/4892
First fixed release: 4.4.0rc5
Last verified: 2026-02-09. Validate in your environment.
When NOT to Use This Fix
- Do not apply this fix if the application does not use pid files for process management.
Verify Fix
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 |
|---|---|
| 4.4.0rc5 | Fixed |
Related Issues
No related fixes found.
Sources
We don’t republish the full GitHub discussion text. Use the links above for context.