As stated, the Selenium Grid Hub receives requests from the automation scripts and redirects them to the appropriate Selenium node. When the request is received, the Hub will analyze the request contents to find a node that can be used to execute the test. For example, if the request wants to run a test using Chrome on macOS, the Hub will go through the existing nodes until it finds one that matches these criteria.

To launch the Grid, follow these steps on your chosen physical or virtual machine:

1. Open a Command Prompt window.
2. Navigate to the directory where the selenium-server-standalone file is located.
3. Write and run this command to launch the Hub of the Selenium Grid:

java -jar selenium-server-standalone-<version>.jar -role
hub

The default value of the Hub port is 4444, but it can be changed by adding the parameter -port to this command.

You should receive a confirmation message, similar to the following one:

20:51:16.748 INFO [GridLauncherV3.launch] - Selenium build info:
version: '3.13.0', revision: '2f0d292'
20:51:16.750 INFO [GridLauncherV3$2.launch] - Launching Selenium
Grid hub on port 4444
2018-07-15 20:51:17.112:INFO::main: Logging initialized @668ms to
org.seleniumhq.jetty9.util.log.StdErrLog
20:51:17.253 INFO [Hub.start] - Selenium Grid hub is up and
running
20:51:17.254 INFO [Hub.start] - Nodes should register to
http://192.168.1.8:4444/grid/register/
20:51:17.254 INFO [Hub.start] - Clients should connect to
http://192.168.1.8:4444/wd/hub