uvicorn Error while closing socket [Errno 9] Bad file

The Fix

Upgrade to version 0.11.4 or later.

Based on closed Kludex/uvicorn issue #184 · 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%.

Jump to Verify Open PR/Commit

@@ -1,5 +1,5 @@
@@ -1,5 +1,5 @@
 from uvicorn.config import Config
-from uvicorn.main import main, run, Server
+from uvicorn.main import Server, main, run

repro.py

[Unit]
Description=gunicorn daemon
Requires=gunicorn.socket
After=network.target

[Service]
PIDFile=/run/gunicorn/pid
User=deploy
Group=deploy
RuntimeDirectory=gunicorn
WorkingDirectory=/home/deploy/django/
ExecStart=/usr/local/bin/gunicorn app.asgi:application --worker-class uvicorn.workers.UvicornWorker --pid /run/gunicorn/pid --bind unix:/run/gunicorn/socket --workers 4 --preload
ExecReload=/bin/kill -s HUP $MAINPID
ExecStop=/bin/kill -s TERM $MAINPID
PrivateTmp=true

[Install]
WantedBy=multi-user.target

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\nUpgrade to version 0.11.4 or later.\nWhen NOT to use: This fix should not be applied if using a different worker class or application server.\n\n

Why This Fix Works in Production

Trigger: Error while closing socket [Errno 9] Bad file descriptor
Mechanism: Improper setup of the event loop in Gunicorn worker class leading to socket errors
Why the fix works: Finesse Gunicorn loop setup to resolve issues with socket errors. (first fixed release: 0.11.4).

Production impact:

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

Shows up under Python 3.6 in real deployments (not just unit tests).
Improper setup of the event loop in Gunicorn worker class leading to socket errors
Surfaces as: Error while closing socket [Errno 9] Bad file descriptor

Proof / Evidence

GitHub issue: #184
Fix PR: https://github.com/kludex/uvicorn/pull/312
First fixed release: 0.11.4
Reproduced locally: No (not executed)
Last verified: 2026-02-09
Confidence: 0.85
Did this fix it?: Yes (upstream fix exists)
Own content ratio: 0.58

Discussion

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

Jump to Sources Open on GitHub

“> /usr/local/lib/python3.6/dist-packages/daphne/server.py Are you running daphne or uvicorn, here? Did you mean to report this on the uvicorn issues?”

@lovelydinosaur · 2018-08-29 · source

“@tomchristie that line is about a bug with raven package (Sentry) and Django Channels, it does not have anything to do with uvicorn”

@felipe3dfx · 2018-08-29 · source

“Somewhat confused by the issue, since running daphne under gunicorn doesn't make sense as far as I can see? (It doens't include a gunicorn worker…”

@lovelydinosaur · 2018-08-29 · source

“Django channels has dependency requirement with daphne, warning issue: https://github.com/django/daphne/issues/195”

@felipe3dfx · 2018-08-29 · source

Failure Signature (Search String)

Error while closing socket [Errno 9] Bad file descriptor

Error Message

Stack trace

error.txt

Error Message
-------------
Error while closing socket [Errno 9] Bad file descriptor

Minimal Reproduction

repro.py

[Unit]
Description=gunicorn daemon
Requires=gunicorn.socket
After=network.target

[Service]
PIDFile=/run/gunicorn/pid
User=deploy
Group=deploy
RuntimeDirectory=gunicorn
WorkingDirectory=/home/deploy/django/
ExecStart=/usr/local/bin/gunicorn app.asgi:application --worker-class uvicorn.workers.UvicornWorker --pid /run/gunicorn/pid --bind unix:/run/gunicorn/socket --workers 4 --preload
ExecReload=/bin/kill -s HUP $MAINPID
ExecStop=/bin/kill -s TERM $MAINPID
PrivateTmp=true

[Install]
WantedBy=multi-user.target

Environment

Python: 3.6

What Broke

Frequent socket errors causing worker exits and delayed responses.

Why It Broke

Improper setup of the event loop in Gunicorn worker class leading to socket errors

Fix Options (Details)

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

Upgrade to version 0.11.4 or later.

When NOT to use: This fix should not be applied if using a different worker class or application server.

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

Fix reference: https://github.com/kludex/uvicorn/pull/312

First fixed release: 0.11.4

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

When NOT to Use This Fix

This fix should not be applied if using a different worker class or application server.

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
0.11.4	Fixed

Related Issues

No related fixes found.

Cluster: uvicorn:configuration-error All hubs All clusters

Related clusters: Data consistency Race condition SSL handshake

Sources

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

uvicorn Error while closing socket [Errno 9] Bad file descriptor (Fix)