[Bug]: browser_mode=builtin fails with "CDP endpoint not ready" — Chromium segfaults (SIGSEGV) when spawned from gunicorn worker (v0.9.3)

Author: nextideasCreated Sep 8, 2026Updated Sep 15, 2026

Labels🐞 Bug⚙️ In-progress

crawl4ai version

0.9.3

Expected Behavior

With browser_config.browser_mode = "builtin", the Docker server should launch its managed Chromium and return the crawled page. This worked on 0.9.1 — we use builtin mode as the only persistent-profile path that passes the server's UNTRUSTED validation (cookies/fingerprints accumulate across calls).

Current Behavior

Any POST /crawl with browser_mode="builtin" returns HTTP 500:

Exception: CDP endpoint at http://localhost:9222 is not ready after startup

ManagedBrowser.start() spawns Chromium via subprocess.Popen(args, stdout=PIPE, stderr=PIPE, preexec_fn=os.setpgrp), and the browser dies within ~500ms with SIGSEGV — logged by _initial_startup_check as:

Browser process terminated during startup | Code: -11 | STDOUT: (empty) | STDERR: (only dbus noise)

The interesting part: the exact same command line (copied from the verbose "Starting browser with args" log), same user, same env and same ulimits works fine when launched (1) via docker exec shell and (2) via a standalone python3 subprocess.Popen with identical pipes/preexec_fn — CDP answers on :9222 within ~1s in both cases. It only segfaults when the parent is the gunicorn UvicornWorker (1 worker, 4 threads, asyncio loop running). Deterministic: persists across container restarts; ~100% failure from the worker, 100% success from any other parent.

Is this reproducible?

Yes

Inputs Causing the Bug

bash

# Any URL triggers it — only browser_mode matters
{
  "urls": ["https://example.com"],
  "browser_config": {"headless": true, "browser_mode": "builtin"},
  "crawler_config": {"cache_mode": "BYPASS"}
}

Steps to Reproduce

bash

docker run -d --name c4ai -p 11235:11235 unclecode/crawl4ai:0.9.3
TOKEN=...  # CRAWL4AI_API_TOKEN from container env
curl -X POST localhost:11235/crawl \
  -H "Authorization: Bearer $TOKEN" -H 'Content-Type: application/json' \
  -d '{"urls":["https://example.com"],"browser_config":{"headless":true,"browser_mode":"builtin"},"crawler_config":{"cache_mode":"BYPASS"}}'
# → 500 {"error":"CDP endpoint at http://localhost:9222 is not ready after startup"}

# Contrast test inside the same container — works:
docker exec c4ai /home/appuser/.cache/ms-playwright/chromium-1234/chrome-linux64/chrome \
  --remote-debugging-port=9222 --user-data-dir=/tmp/t --headless=new --no-sandbox \
  --disable-dev-shm-usage about:blank
# → "DevTools listening on ws://127.0.0.1:9222/..." within ~1s

Code snippets

python

# Standalone inside the container — this WORKS (CDP OK in 1s),
# which isolates the bug to the gunicorn-worker parent context:
import subprocess, os, time, urllib.request
args = ["/home/appuser/.cache/ms-playwright/chromium-1234/chrome-linux64/chrome",
        "--remote-debugging-port=9222", "--user-data-dir=/tmp/bt", "--headless=new",
        "--window-size=1080,600", "--no-sandbox", "--disable-dev-shm-usage",
        "--disable-gpu", "about:blank"]
p = subprocess.Popen(args, stdout=subprocess.PIPE, stderr=subprocess.PIPE, preexec_fn=os.setpgrp)
time.sleep(1)
print(urllib.request.urlopen("http://localhost:9222/json/version", timeout=2).read())

OS

Linux x86_64 (Docker image unclecode/crawl4ai:0.9.3; host with standard Docker defaults, shm_size 4gb, ulimits nofile 65536)

Python version

3.12.14

Browser

No response

Browser version

Chromium (Playwright-installed, launched by ManagedBrowser)

Error logs & Screenshots (if applicable)

[CRAWL] api - ERROR - Crawl error: CDP endpoint at http://localhost:9222 is not ready after startup Traceback (most recent call last): File "/app/api.py", line 714, in handle_crawl_request crawler = await get_crawler(browser_config) File "/app/crawler_pool.py", line 114, in get_crawler await crawler.start() File "/usr/local/lib/python3.12/site-packages/crawl4ai/async_webcrawler.py", line 183, in start ... Exception: CDP endpoint at http://localhost:9222 is not ready after startup

[BROWSER] Browser process terminated during startup | Code: -11 | STDOUT: | STDERR: [45969:45984:ERROR:dbus/bus.cc:405] Failed to connect to the bus: Failed to connect to socket /run/dbus/system_bus_socket: No such file or directory

Launch args used (from verbose log):

/home/appuser/.cache/ms-playwright/chromium-1234/chrome-linux64/chrome --remote-debugging-port=9222 --user-data-dir=/tmp/browser-profile-XXXX --headless=new --window-size=1080,600 --no-sandbox --disable-dev-shm-usage --no-first-run --no-default-browser-check --disable-infobars --ignore-certificate-errors --disable-blink-features=AutomationControlled --disable-gpu ...