As a senior PHP and JS web developer, you may encounter scenarios where you need to restart Cassandra DB and enable encryption at rest. This process is crucial for ensuring the security and integrity of your data. Below are the steps you can follow to achieve this:

Restarting Cassandra DB:

1. Stop the Cassandra service by running the following command:

sudo systemctl stop cassandra

2. Verify that the Cassandra service has stopped successfully by checking its status:

sudo systemctl status cassandra

3. Restart the Cassandra service with the following command:

sudo systemctl start cassandra

4. Verify that the Cassandra service has started successfully:

sudo systemctl status cassandra

Enabling Encryption at Rest:

1. Open the Cassandra configuration file for editing. This file is usually located at /etc/cassandra/cassandra.yaml:

sudo nano /etc/cassandra/cassandra.yaml

2. Search for the enable_user_defined_functions parameter in the configuration file.

3. Set the enable_user_defined_functions parameter to true to enable encryption at rest:

enable_user_defined_functions: true

4. Save the changes to the configuration file and exit the editor.

5. Restart the Cassandra service to apply the changes:

sudo systemctl restart cassandra

Verifying Encryption at Rest:

1. Connect to the Cassandra shell by running the following command:

cqlsh

2. Run the following CQL query to verify if encryption at rest is enabled:

SELECT * FROM system_schema.keyspaces;

3. If encryption at rest is enabled, you should see encrypted data in the output.

By following these steps, you can successfully restart Cassandra DB and enable encryption at rest to enhance the security of your data.