ORA-12154: TNS: Could Not Resolve the Connect Identifier Specified

The ORA-12154 error, TNS: Could Not Resolve the Connect Identifier Specified , typically occurs when attempting to connect to an Oracle database using a service name or alias that cannot be resolved by the Oracle client. This error indicates that the client cannot locate the database specified in the connection string.

Following are some steps you can take to resolve the ORA-12154 error :

1. Check the connection string: Verify that the connection string you are using is correct. Ensure that the hostName, port number, and service name are accurate. Pay attention to any typographical errors or missing information.

2. Verify the tnsnames.ora file: The tnsnames.ora file contains the connection information for Oracle databases. It is usually located in the $ORACLE_HOME/network/admin directory. Open the file and check if the entry for your database is present and correct. Verify the service name, host, port, and other connection details.

3. Ensure the Oracle Net service is running: The Oracle Net service, often referred to as the TNS Listener needs to be running on the database server. If the LISTENER is not running, start it using the following command: For Linux
lsnrctl start LISTENER_NAME  

4. Test the connection using tnsping: Use the tnsping utility to test the connectivity to the database. Open a command prompt and run the following command:
tnsping service_name  

Replace service_name with the service name or alias specified in your connection string. If tnsping is successful and returns the proper response, it indicates that the connection information is correctly configured.

5. Check the environment variables: Ensure that the ORACLE_HOME and TNS_ADMIN environment variables are correctly set. ORACLE_HOME should point to the Oracle installation directory, and TNS_ADMIN should point to the directory containing the tnsnames.ora file. Update these variables if necessary.

6. Restart the Oracle services: If you made any changes to the tnsnames.ora file or environment variables, restart the Oracle services, including the listener service and any relevant database services.

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