SeleniumHQ/selenium · critical · WebDriverException

Service path cannot be None.

Error message

Service path cannot be None.

What it means

Raised by Service.start() at the very first line if self._path is None. The _path is computed in __init__ as 'env_path() or executable_path', so it is None only when no driver_path_env_key env var is set AND no executable_path was passed to the constructor. This guard fires before any process is launched.

Source

Thrown at py/selenium/webdriver/common/service.py:107

        raise NotImplementedError("This method needs to be implemented in a sub class")

    @property
    def path(self) -> str:
        return self._path or ""

    @path.setter
    def path(self, value: str) -> None:
        self._path = str(value)

    def start(self) -> None:
        """Starts the Service.

        Raises:
            WebDriverException: Raised either when it can't start the service
                or when it can't connect to the service
        """
        if self._path is None:
            raise WebDriverException("Service path cannot be None.")
        self._start_process(self._path)

        count = 0
        try:
            while True:
                self.assert_process_still_running()
                if self.is_connectable():
                    break
                # sleep increasing: 0.01, 0.06, 0.11, 0.16, 0.21, 0.26, 0.31, 0.36, 0.41, 0.46, 0.5
                sleep(min(0.01 + 0.05 * count, 0.5))
                count += 1
                if count == 70:
                    raise WebDriverException(f"Can not connect to the Service {self._path}")
        except BaseException:
            try:
                self.stop()
            except Exception:
                logger.error("Error stopping service after a failed start.", exc_info=True)

View on GitHub (pinned to aa36b38e69)

Solutions

1. Pass an explicit driver path: Service(executable_path='/path/to/chromedriver').
2. Set the driver env var for your browser, e.g. export SE_GECKODRIVER=/usr/bin/geckodriver.
3. Let Selenium Manager resolve the driver automatically by upgrading selenium and not overriding executable_path.
4. Verify the variable you pass to executable_path is not None before constructing the Service.

Example fix

# before
service = Service(executable_path=None)  # or just Service()
service.start()  # -> Service path cannot be None.

# after
from selenium.webdriver.chrome.service import Service
service = Service(executable_path='/usr/local/bin/chromedriver')

from selenium.webdriver.chrome.service import Service
path = os.getenv('SE_CHROMEDRIVER') or '/usr/local/bin/chromedriver'
assert path and Path(path).is_file(), 'No driver path; set SE_CHROMEDRIVER or pass executable_path'
service = Service(executable_path=path)

def is_valid_driver_path(p) -> bool:
    return isinstance(p, str) and p and Path(p).is_file()

from selenium.common.exceptions import WebDriverException
try:
    service.start()
except WebDriverException as e:
    if 'Service path cannot be None' in str(e):
        service.path = '/usr/local/bin/chromedriver'
        service.start()

When it happens

Trigger: Constructing a browser-specific Service with executable_path=None (the default) while the corresponding driver env var (e.g. SE_CHROMEDRIVER, SE_GECKODRIVER, SE_EDGEDRIVER) is unset, and then calling .start(). This typically happens only when Selenium Manager is also unavailable to supply the path automatically.

Common situations: Disabling Selenium Manager or using a very old selenium version, explicitly passing executable_path=None, or a misconfigured CI where the expected env var is empty rather than absent. Also seen when someone passes executable_path as a variable that evaluated to None.

Related errors

• Can not connect to the Service {self._path}
• Service {self._path} unexpectedly exited. Status code was: {
• service_args must be a sequence
• invalid port: #{@port}
• Unable to obtain browser driver. For more informatio

AI-assisted analysis of SeleniumHQ/selenium@aa36b38e69 (2026-08-14). Data as JSON: /api/errors/687e78de5ab659f2. Report an issue: GitHub.