Overview:

The customer has encountered an issue where the Ambari monitoring system indicates that the NameNode service in their Hadoop cluster is stopped. The NameNode is a critical component of Hadoop responsible for managing the file system metadata. To resolve this issue, we will outline the steps to start the NameNode service using the Ambari tool.

Solution:

To start the NameNode service using Ambari, follow these steps:

1. Access the Ambari web interface using a web browser.
2. Log in with the appropriate credentials.
3. Navigate to the "Services" page.
4. Locate and click on the "HDFS" service.
5. In the HDFS service summary page, find and click on the "NameNode" component.
6. In the NameNode component page, locate the "Service Actions" section.
7. Select "Start" from the drop-down menu in the "Service Actions" section.
8. Monitor the progress and status displayed by Ambari.
9. Verify the NameNode status on the HDFS service summary page.

If the Ambari GUI is not accessible then command line method can be followed as specified below:

Command Line Method:

1. Open a terminal or command prompt.
2. Navigate to the Hadoop installation directory.
3. Locate the sbin folder.
4. Run the command: ./hadoop-daemon.sh start namenode.
5. If prompted, run the command with administrative privileges (e.g., sudo on Linux or macOS).
6. Monitor the output for confirmation that the NameNode has started.
7. Verify the NameNode service by running: jps.
8. Look for the NameNode process in the output.

Verification

By following these steps, the NameNode service should be started, and the Ambari monitoring system should reflect the correct status of the service.