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Configuring Components

Here you can see how each Grid component can be configured individually based on common configuration values and component-specific configuration values.

1 - Config help

Get information about all the available options to configure Grid.

The help commands display information based on the current code implementation. Hence, it will provide accurate information in case the documentation is not updated. It is the easiest way to learn about Grid 4 configuration for any new version.

Info Command

The info command provides detailed docs on the following topics:

  • Configuring Selenium
  • Security
  • Session Map setup
  • Tracing

Config help

Quick config help and overview is provided by running:

java -jar selenium-server-<version>.jar info config


To get details on setting up the Grid servers for secure communication and node registration:

java -jar selenium-server-<version>.jar info security

Session Map setup

By default, Grid uses a local session map to store session information. Grid supports additional storage options like Redis and JDBC - SQL supported databases. To set up different session storage, use the following command to get setup steps:

java -jar selenium-server-<version>.jar info sessionmap

Setting up tracing with OpenTelemetry and Jaeger

By default, tracing is enabled. To export traces and visualize them via Jaeger, use the following command for instructions:

java -jar selenium-server-<version>.jar info tracing

List the Selenium Grid commands

java -jar selenium-server-<version>.jar --config-help

It will show all the available commands and description for each one.

Component help commands

Pass –help config option after the Selenium role to get component-specific config information.


java -jar selenium-server-<version>.jar standalone --help


java -jar selenium-server-<version>.jar hub --help


java -jar selenium-server-<version>.jar sessions --help

New Session Queue

java -jar selenium-server-<version>.jar sessionqueue --help


java -jar selenium-server-<version>.jar distributor --help


java -jar selenium-server-<version>.jar router --help


java -jar selenium-server-<version>.jar node --help

2 - CLI Options

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.




--grid-modelstringorg.openqa.selenium.grid.distributor.GridModelFull classname of non-default grid model. This is used to store the states of all the registered Nodes.
--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-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


--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.
--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 processos 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.


--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


--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.
--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

3 - Toml Options

Grid configuration examples using Toml files.

All the options shown in CLI options can be configured through a TOML file. This page shows configuration examples for the different Grid components.

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.


Selenium Grid uses TOML format for config files. The config file consists of sections and each section has options and its respective value(s).

Refer to the TOML documentation for detailed usage guidance. In case of parsing errors, validate the config using TOML linter.

The general configuration structure has the following pattern:



Below are some examples of Grid components configured with a Toml file, the component can be started in the following way:

java -jar selenium-server-<version>.jar <component> --config /path/to/file/<file-name>.toml


A Standalone server, running on port 4449, and a new session request timeout of 500 seconds.

port = 4449

session-request-timeout = 500

Specific browsers and a limit of max sessions

A Standalone server or a Node which only has Firefox and Chrome enabled by default.

drivers = ["chrome", "firefox"]
max-sessions = 3

Configuring and customising drivers

Standalone or Node server with customised drivers, which allows things like having Firefox Beta or Nightly, and having different browser versions.

detect-drivers = false
max-sessions = 100
display-name = "Firefox Nightly"
stereotype = "{\"browserName\": \"firefox\", \"browserVersion\": \"93\", \"platformName\": \"MAC\", \"moz:firefoxOptions\": {\"binary\": \"/Applications/Firefox\"}}"
display-name = "Chrome Beta"
stereotype = "{\"browserName\": \"chrome\", \"browserVersion\": \"94\", \"platformName\": \"MAC\", \"goog:chromeOptions\": {\"binary\": \"/Applications/Google Chrome Chrome Beta\"}}"
display-name = "Chrome Dev"
stereotype = "{\"browserName\": \"chrome\", \"browserVersion\": \"95\", \"platformName\": \"MAC\", \"goog:chromeOptions\": {\"binary\": \"/Applications/Google Chrome Chrome Dev\"}}"
webdriver-executable = '/path/to/chromedriver/95/chromedriver'

Standalone or Node with Docker

A Standalone or Node server that is able to run each new session in a Docker container. Disabling drivers detection, having maximum 2 concurrent sessions. Stereotypes configured need to be mapped to a Docker image, and the Docker daemon needs to be exposed via http/tcp.

detect-drivers = false
max-sessions = 2

configs = 
        "selenium/standalone-chrome:93.0", "{\"browserName\": \"chrome\", \"browserVersion\": \"91\"}", 
        "selenium/standalone-firefox:92.0", "{\"browserName\": \"firefox\", \"browserVersion\": \"92\"}"
url = "http://localhost:2375"
video-image = "selenium/video:latest"

Relaying commands to a service endpoint that supports WebDriver

It is useful to connect an external service that supports WebDriver to Selenium Grid. An example of such service could be a cloud provider or an Appium server. In this way, Grid can enable more coverage to platforms and versions not present locally.

The following is an en example of connecting an Appium server to Grid.

port = 5555

detect-drivers = false

# Default Appium server endpoint
url = "http://localhost:4723/wd/hub"
status-endpoint = "/status"
# Stereotypes supported by the service
configs = [
  "1", "{\"browserName\": \"chrome\", \"platformName\": \"android\", \"appium:platformVersion\": \"11\"}"

Basic auth enabled

It is possible to protect a Grid with basic auth by configuring the Router/Hub/Standalone with a username and password. This user/password combination will be needed when loading the Grid UI or starting a new session.

username = "admin"
password = "myStrongPassword"

Here is a Java example showing how to start a session using the configured user and password.

URL gridUrl = new URL("http://admin:myStrongPassword@localhost:4444");
RemoteWebDriver webDriver = new RemoteWebDriver(gridUrl, new ChromeOptions());