{"record":{"id":"0f203fe560b836b0","repo":"unclecode/crawl4ai","slug":"failed-to-start-browser-e-0f203f","errorCode":null,"errorMessage":"Failed to start browser: {e}","messagePattern":"Failed to start browser: (.+?)","errorType":"exception","errorClass":"Exception","httpStatus":null,"severity":"critical","filePath":"crawl4ai/browser_manager.py:277","lineNumber":7112,"sourceCode":"                    stderr=subprocess.PIPE,\n                    creationflags=subprocess.DETACHED_PROCESS | subprocess.CREATE_NEW_PROCESS_GROUP\n                )\n            else:\n                self.browser_process = subprocess.Popen(\n                    args, \n                    stdout=subprocess.PIPE, \n                    stderr=subprocess.PIPE,\n                    preexec_fn=os.setpgrp  # Start in a new process group\n                )\n                \n            # We'll monitor for a short time to make sure it starts properly, but won't keep monitoring\n            await asyncio.sleep(0.5)  # Give browser time to start\n            await self._initial_startup_check()\n            await asyncio.sleep(2)  # Give browser time to start\n            return f\"http://{self.host}:{self.debugging_port}\"\n        except Exception as e:\n            await self.cleanup()\n            raise Exception(f\"Failed to start browser: {e}\")\n\n    async def _initial_startup_check(self):\n        \"\"\"\n        Perform a quick check to make sure the browser started successfully.\n        This only runs once at startup rather than continuously monitoring.\n        \"\"\"\n        if not self.browser_process:\n            return\n            \n        # Check that process started without immediate termination\n        await asyncio.sleep(0.5)\n        if self.browser_process.poll() is not None:\n            # Process already terminated\n            stdout, stderr = b\"\", b\"\"\n            try:\n                stdout, stderr = self.browser_process.communicate(timeout=0.5)\n            except subprocess.TimeoutExpired:\n                pass","sourceCodeStart":7094,"sourceCodeEnd":7130,"githubUrl":"https://github.com/unclecode/crawl4ai/blob/7e801521428ee12509994d39151006f64055ebe3/deploy/docker/c4ai-code-context.md#L7094-L7130","documentation":"Raised by the managed/native browser launcher when the subprocess launch, the initial startup check, or the fixed-delay readiness waits raise or time out. Before raising it calls await self.cleanup() (killing the process and removing the temp profile dir), then wraps the original failure in a generic Exception prefixed with 'Failed to start browser:'.","triggerScenarios":"Managed/Native browser mode where the Chrome/Firefox binary is missing or not executable; the debugging port is already in use by another instance; the process dies within the first ~2.5s (crash on startup, bad --headless flag for the installed version); sandbox/environment problems (no /dev/shm, missing shared libs in a container); any exception during subprocess creation such as FileNotFoundError.","commonSituations":"Docker images without a browser installed or with an incompatible browser version; user_data_dir on a read-only volume; leftover browser processes holding the debugging port; SELinux/AppArmor denying exec; CI runners lacking sandbox support requiring --no-sandbox.","solutions":["Read the text after 'Failed to start browser:' to identify the root cause (FileNotFoundError means the binary path is wrong; 'address already in use' means the port is taken)","Verify the browser binary exists and runs: chromium --version; fix browser_type/binary path in the config","Kill stale browser processes or set a fresh debugging_port / user_data_dir","In Docker/CI, ensure required shared libraries are installed and pass --no-sandbox if the environment lacks a sandbox","Retry once at the call site — cleanup() has already run, so a retry starts from a clean state"],"exampleFix":"# before\nurl = await browser.start()  # raises: Failed to start browser: ...\n# after\nfrom pathlib import Path\nif not Path(browser_config.binary or shutil.which(\"chromium\")).exists():\n    raise RuntimeError(\"browser binary missing — install chromium first\")\ntry:\n    url = await browser.start()\nexcept Exception as e:\n    logger.error(\"browser start failed: %s\", e)\n    raise\n","handlingStrategy":"retry","validationCode":"import shutil, socket\n\ndef browser_launchable(binary: str | None, port: int) -> list[str]:\n    problems = []\n    if not (binary and __import__('pathlib').Path(binary).exists()) and not shutil.which(binary or \"chromium\"):\n        problems.append(\"browser binary not found\")\n    with socket.socket() as s:\n        try:\n            s.bind((\"127.0.0.1\", port))\n        except OSError:\n            problems.append(f\"debugging port {port} already in use\")\n    return problems","typeGuard":null,"tryCatchPattern":"try:\n    ws_url = await browser.start()\nexcept Exception as e:\n    logger.error(\"browser failed to start (cleanup already ran): %s\", e)\n    if \"not found\" in str(e) or \"address already in use\" in str(e):\n        raise  # fix environment, retrying will not help\n    await asyncio.sleep(2)\n    ws_url = await browser.start()  # state is clean after internal cleanup()","preventionTips":["Install and verify the browser binary (chromium --version) before enabling managed/native browser mode","Allocate unique debugging ports per concurrent crawler instance","In Docker, install browser dependencies and pass --no-sandbox when there is no sandbox","Pre-check port availability and binary existence before calling start()"],"tags":["crawl4ai","browser-launch","subprocess","environment"],"backgroundTag":null,"analyzedSha":"7e801521428ee12509994d39151006f64055ebe3","analyzedAt":"2026-08-14T20:46:20.673Z","schemaVersion":2},"datasetVersion":"2026-08-15T17:31:12.345Z"}