When connecting a Node.js app to a MySQL database, an error message may appear indicating that there's a problem connecting to the local MySQL server through the socket file `/tmp/mysql.sock`. The issue typically arises from incorrect configuration or mismanagement of the socket file location. To resolve this error, one must first verify the MySQL server status by running `service mysql status`, and then check the MySQL server configuration to ensure that the socket file location matches the actual path on the system. After making necessary changes, restarting the MySQL server is crucial for the updates to take effect. Finally, when connecting to MySQL in the Node.js app, it's essential to verify that the specified socket file path in the connection settings matches the correct location of the socket file.