CLI options in the Selenium Grid

All Grid components configuration CLI options in detail.

Different sections are available to configure a Grid. Each section has options can be configured through command line arguments.

A complete description of the component to section mapping can be seen below.

Note that this documentation could be outdated if an option was modified or added but has not been documented yet. In case you bump into this situation, please check the “Config help” section and feel free to send us a pull request updating this page.




--healthcheck-intervalint120How often, in seconds, will the health check run for all Nodes. This ensures the server can ping all the Nodes successfully.
--distributorurihttp://localhost:5553Url of the distributor.
--distributor-hoststringlocalhostHost on which the distributor is listening.
--distributor-implementationstringorg.openqa.selenium.grid.distributor.local.LocalDistributorFull class name of non-default distributor implementation
--distributor-portint5553Port on which the distributor is listening.
--reject-unsupported-capsbooleanfalseAllow the Distributor to reject a request immediately if the Grid does not support the requested capability. Rejecting requests immediately is suitable for a Grid setup that does not spin up Nodes on demand. class name of non-default slot matcher to use. This is used to determine whether a Node can support a particular session.
--slot-selectorstringorg.openqa.selenium.grid.distributor.selector.DefaultSlotSelectorFull class name of non-default slot selector. This is used to select a slot in a Node once the Node has been matched.


--docker-assets-pathstring/opt/selenium/assetsAbsolute path where assets will be stored
--docker-string[]selenium/standalone-firefox:latest '{"browserName": "firefox"}'Docker configs which map image name to stereotype capabilities (example `-D selenium/standalone-firefox:latest ‘{“browserName”: “firefox”}’)
--docker-devicesstring[]/dev/kvm:/dev/kvmExposes devices to a container. Each device mapping declaration must have at least the path of the device in both host and container separated by a colon like in this example: /device/path/in/host:/device/path/in/container
--docker-hoststringlocalhostHost name where the Docker daemon is running
--docker-portint2375Port where the Docker daemon is running
--docker-urlstringhttp://localhost:2375URL for connecting to the Docker daemon
--docker-video-imagestringselenium/video:latestDocker image to be used when video recording is enabled


--bind-busbooleanfalseWhether the connection string should be bound or connected.
When true, the component will be bound to the Event Bus (as in the Event Bus will also be started by the component, typically by the Distributor and the Hub).
When false, the component will connect to the Event Bus. class name of non-default event bus implementation
--publish-eventsstringtcp://*:4442Connection string for publishing events to the event bus
--subscribe-eventsstringtcp://*:4443Connection string for subscribing to events from the event bus


--http-logsbooleanfalseEnable http logging. Tracing should be enabled to log http logs.
--log-encodingstringUTF-8Log encoding
--logstringWindows path example :

Linux/Unix/MacOS path example :
File to write out logs. Ensure the file path is compatible with the operating system’s file path.
--log-levelstring“INFO”Log level. Default logging level is INFO. Log levels are described here
--plain-logsbooleantrueUse plain log lines
--structured-logsbooleanfalseUse structured logs
--tracingbooleantrueEnable trace collection
--log-timestamp-formatstringHH:mm:ss.SSSAllows the configure log timestamp format


--relax-checksbooleanfalseRelax checks on origin header and content type of incoming requests, in contravention of strict W3C spec compliance.


--detect-driversbooleantrueAutodetect which drivers are available on the current system, and add them to the Node.
--driver-configurationstring[]display-name="Firefox Nightly" max-sessions=2 webdriver-path="/usr/local/bin/geckodriver" stereotype='{"browserName": "firefox", "browserVersion": "86", "moz:firefoxOptions": {"binary":"/Applications/Firefox"}}'List of configured drivers a Node supports. It is recommended to provide this type of configuration through a toml config file to improve readability
--driver-factorystring[]org.openqa.selenium.example.LynxDriverFactory '{"browserName": "lynx"}'Mapping of fully qualified class name to a browser configuration that this matches against.
--driver-implementationstring[]"firefox"Drivers that should be checked. If specified, will skip autoconfiguration.
--node-implementationstring"org.openqa.selenium.grid.node.local.LocalNodeFactory"Full classname of non-default Node implementation. This is used to manage a session’s lifecycle.
--grid-urlstringhttps://grid.example.comPublic URL of the Grid as a whole (typically the address of the Hub or the Router)
--heartbeat-periodint60How often, in seconds, will the Node send heartbeat events to the Distributor to inform it that the Node is up.
--max-sessionsint8Maximum number of concurrent sessions. Default value is the number of available processors.
--override-max-sessionsbooleanfalseThe # of available processors is the recommended max sessions value (1 browser session per processor). Setting this flag to true allows the recommended max value to be overwritten. Session stability and reliability might suffer as the host could run out of resources.
--register-cycleint10How often, in seconds, the Node will try to register itself for the first time to the Distributor.
--register-periodint120How long, in seconds, will the Node try to register to the Distributor for the first time. After this period is completed, the Node will not attempt to register again.
--session-timeoutint300Let X be the session-timeout in seconds. The Node will automatically kill a session that has not had any activity in the last X seconds. This will release the slot for other tests.
--vnc-env-varstringSTART_XVFBEnvironment variable to check in order to determine if a vnc stream is available or not.
--no-vnc-portint7900If VNC is available, sets the port where the local noVNC stream can be obtained
--drain-after-session-countint1Drain and shutdown the Node after X sessions have been executed. Useful for environments like Kubernetes. A value higher than zero enables this feature.
--hubstringhttp://localhost:4444The address of the Hub in a Hub-and-Node configuration. Can be a hostname or IP address (hostname), in which case the Hub will be assumed to be http://hostname:4444, the --grid-url will be the same --publish-events will be tcp://hostname:4442 and --subscribe-events will be tcp://hostname:4443. If hostname contains a port number, that will be used for --grid-url but the URIs for the event bus will remain the same. Any of these default values may be overridden but setting the correct flags. If the hostname has a protocol (such as https) that will be used too.
--enable-cdpbooleantrueEnable CDP proxying in Grid. A Grid admin can disable CDP if the network doesnot allow websockets. True by default.
--downloads-pathstring/usr/downloadsThe default location wherein all browser triggered file downloads would be available to be retrieved from. This is usually the directory that you configure in your browser as the default location for storing downloaded files.
--selenium-managerbooleanfalseWhen drivers are not available on the current system, use Selenium Manager. False by default.


--service-urlstringhttp://localhost:4723URL for connecting to the service that supports WebDriver commands like an Appium server or a cloud service.
--service-hoststringlocalhostHost name where the service that supports WebDriver commands is running
--service-portint4723Port where the service that supports WebDriver commands is running
--service-status-endpointstring/statusOptional, endpoint to query the WebDriver service status, an HTTP 200 response is expected
--service-configurationstring[]max-sessions=2 stereotype='{"browserName": "safari", "platformName": "iOS", "appium:platformVersion": "14.5"}}'Configuration for the service where calls will be relayed to. It is recommended to provide this type of configuration through a toml config file to improve readability.


--passwordstringmyStrongPasswordPassword clients must use to connect to the server. Both this and the username need to be set in order to be used.
--usernamestringadminUser name clients must use to connect to the server. Both this and the password need to be set in order to be used.


--allow-corsbooleantrueWhether the Selenium server should allow web browser connections from any host
--hoststringlocalhostServer IP or hostname: usually determined automatically.
--bind-hostbooleantrueWhether the server should bind to the host address/name, or only use it to" report its reachable url. Helpful in complex network topologies where the server cannot report itself with the current IP/hostname but rather an external IP or hostname (e.g. inside a Docker container)
--https-certificatepath/path/to/cert.pemServer certificate for https. Get more detailed information by running “java -jar selenium-server.jar info security”
--https-private-keypath/path/to/key.pkcs8Private key for https. Get more detailed information by running “java -jar selenium-server.jar info security”
--max-threadsint24Maximum number of listener threads. Default value is: (available processors) * 3.
--portint4444Port to listen on. There is no default as this parameter is used by different components, for example, Router/Hub/Standalone will use 4444 and Node will use 5555.


--sessionqueueurihttp://localhost:1237Address of the session queue server.
-sessionqueue-hoststringlocalhostHost on which the session queue server is listening.
--sessionqueue-portint1234Port on which the session queue server is listening.
--session-request-timeoutint300Timeout in seconds. A new incoming session request is added to the queue. Requests sitting in the queue for longer than the configured time will timeout.
--session-retry-intervalint5Retry interval in seconds. If all slots are busy, new session request will be retried after the given interval.


--sessionsurihttp://localhost:1234Address of the session map server.
--sessions-hoststringlocalhostHost on which the session map server is listening.
--sessions-portint1234Port on which the session map server is listening.

Configuration examples

All the options mentioned above can be used when starting the Grid components. They are a good way of exploring the Grid options, and trying out values to find a suitable configuration.

We recommend the use of Toml files to configure a Grid. Configuration files improve readability, and you can also check them in source control.

When needed, you can combine a Toml file configuration with CLI arguments.

Command-line flags

To pass config options as command-line flags, identify the valid options for the component and follow the template below.

java -jar selenium-server-<version>.jar <component> --<option> value

Standalone, setting max sessions and main port

java -jar selenium-server-<version>.jar standalone --max-sessions 4 --port 4444

Hub, setting a new session request timeout, a main port, and disabling tracing

java -jar selenium-server-<version>.jar hub --session-request-timeout 500 --port 3333 --tracing false

Node, with 4 max sessions, with debug(fine) log, 7777 as port, and only with Firefox and Edge

java -jar selenium-server-<version>.jar node --max-sessions 4 --log-level "fine" --port 7777 --driver-implementation "firefox" --driver-implementation "edge"

Distributor, setting Session Map server url, Session Queue server url, and disabling bus

java -jar selenium-server-<version>.jar distributor --sessions http://localhost:5556 --sessionqueue http://localhost:5559 --bind-bus false

Setting custom capabilities for matching specific Nodes

Important: Custom capabilities need to be set in the configuration in all Nodes. They also need to be included always in every session request.

Start the Hub
java -jar selenium-server-<version>.jar hub
Start the Node A with custom cap set to true
java -jar selenium-server-<version>.jar node --detect-drivers false --driver-configuration display-name="Chrome (custom capability true)" max-sessions=1 stereotype='{"browserName":"chrome","gsg:customcap":true}' --port 6161
Start the Node B with custom cap set to false
java -jar selenium-server-<version>.jar node --detect-drivers false --driver-configuration display-name="Chrome (custom capability true)" max-sessions=1 stereotype='{"browserName":"chrome","gsg:customcap":false}' --port 6262
Matching Node A
ChromeOptions options = new ChromeOptions();
options.setCapability("gsg:customcap", true);
WebDriver driver = new RemoteWebDriver(new URL("http://localhost:4444"), options);

Set the custom capability to false in order to match the Node B.

Specifying path from where downloaded files can be retrieved

At times a test may need to access files that were downloaded by it on the Node. To retrieve such files, following can be done.

Start the Hub
java -jar selenium-server-<version>.jar hub
Start the Node with downloads path specified
java -jar selenium-server-<version>.jar node --downloads-path /usr/downloads
Important information when dowloading a file:
  • The endpoint to GET from is /session/<sessionId>/se/file?filename=
  • The session needs to be active in order for the command to work.
  • The response blob contains two keys,
    • filename - Same as what was specified in the request.
    • contents - Base64 encoded zipped contents of the file.
  • The file contents are Base64 encoded and they need to be unzipped.
Sample that retrieves the downloaded file

Assuming the downloaded file is named my_file.pdf, and using curl, the file could be downloaded with the following command:

curl -X GET "http://localhost:4444/session/<sessionId>/se/file?filename=my_file.pdf"

Below is an example in Java that shows how to download a file named my_file.pdf.

import static org.openqa.selenium.remote.http.Contents.string;

import java.util.Map;
import java.util.concurrent.TimeUnit;
import org.openqa.selenium.By;
import org.openqa.selenium.WebElement;
import org.openqa.selenium.firefox.FirefoxOptions;
import org.openqa.selenium.json.Json;
import org.openqa.selenium.remote.RemoteWebDriver;
import org.openqa.selenium.remote.http.HttpClient;
import org.openqa.selenium.remote.http.HttpMethod;
import org.openqa.selenium.remote.http.HttpRequest;
import org.openqa.selenium.remote.http.HttpResponse;

public class DownloadsSample {

  public static void main(String[] args) throws InterruptedException, IOException {
    // Make sure the following directory exists on your machine
    File dirToCopyTo = new File("/usr/downloads/file");
    // Assuming the Grid is running locally.
    URL gridUrl = new URL("http://localhost:4444");
    RemoteWebDriver driver = new RemoteWebDriver(gridUrl, firefoxOptions());
    // This public website resets the available files for dowload on a daily basis, 
    // check the name of the file that will be downloaded and replace it below.
    WebElement element = driver.findElement(By.cssSelector(".example a"));;

    // The download happens in a remote Node, which makes difficult to know when the file 
    // has been completely downloaded. For demonstration purposes, this example uses a 
    // 10 second sleep which should be enough time for a file to be downloaded. 
    // We strongly recommend to avoid hardcoded sleeps, and ideally, to modify your 
    // application under test so it offers a way to know when the file has been completely 
    // downloaded. 

    HttpRequest request = new HttpRequest(HttpMethod.GET, String.format("/session/%s/se/file", driver.getSessionId()));
    request.addQueryParameter("filename", "my_file.pdf");
    try (HttpClient client = HttpClient.Factory.createDefault().createClient(gridUrl)) {
      HttpResponse response = client.execute(request);
      Map<String, Object> map = new Json().toType(string(response), Json.MAP_TYPE);
      // The returned map would contain 2 keys,
      // filename - This represents the name of the file (same as what was provided by the test)
      // contents - Base64 encoded String which contains the zipped file.
      String encodedContents = map.get("contents").toString();

      //The file contents would always be a zip file and has to be unzipped.
      Zip.unzip(encodedContents, dirToCopyTo);
    } finally {

  private static FirefoxOptions firefoxOptions() {
    FirefoxOptions options = new FirefoxOptions();
    // Options specific for Firefox to avoid prompting a dialog for downloads. They might 
    // change in the future, so please refer to the Firefox documentation for up to date details.
    options.addPreference("", false);
        "images/jpeg, application/pdf, application/octet-stream");
    options.addPreference("pdfjs.disabled", true);
    return options;
Last modified February 22, 2023: Changing value for flag (e99c6d18dc2)