ORA-12154 database link | tns:could not resolve the connect identifier specified solutions and commands

The Oracle error ORA-12154: TNS

not resolve the connect identifier specified occurs when Oracle is unable to find the specified connect identifier in your TNSNAMES.ORA configuration file. This error generally arises when there is a problem with the database link or when the connection identifier is incorrect or missing. Here are some solutions and steps to resolve this issue:

Solutions

1. Check TNSNAMES.ORA File

Make sure that the TNSNAMES.ORA file is correctly configured and includes the required connect identifier.

The TNSNAMES.ORA file is usually located in the ORACLE_HOME/network/admin/ directory.

Example of an entry in TNSNAMES.ORA:

DB_ALIAS =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = myhost.example.com)(PORT = 1521))
    (CONNECT_DATA =
      (SERVICE_NAME = myservice)
    )
  )

Ensure that the alias (e.g., DB_ALIAS) is correct and used in your connection string.

2. Verify Connection String

Double-check the connection string in your application or SQL script.

Example connection string:

CONNECT user/password@DB_ALIAS

The alias DB_ALIAS must match an entry in the TNSNAMES.ORA file.

3. Ensure Correct Environment Variables

Ensure that the ORACLE_HOME and TNS_ADMIN environment variables are set correctly, pointing to the correct Oracle installation and network directory.

Use the following commands to check the environment variables:

On Windows:

echo %ORACLE_HOME%

echo %TNS_ADMIN%

On Linux/Unix:

echo $ORACLE_HOME

echo $TNS_ADMIN

If these variables are not set or are incorrect, set them appropriately.

4. Use the Full Connection String

Instead of relying on the TNSNAMES.ORA file, try using the full connect string in your connection command:

Example:

CONNECT user/password@(DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=myhost.example.com)(PORT=1521))(CONNECT_DATA=(SERVICE_NAME=myservice)))

5. Check Oracle Listener

Ensure that the Oracle listener is running and configured correctly. You can check the listener status with the following command:

lsnrctl status

If the listener is not running, start it using:

lsnrctl start

6. Firewall/Network Configuration

Ensure that there are no firewall or network issues preventing the connection.

Test the connection by pinging the host or using the tnsping utility:

tnsping DB_ALIAS

7. Check for Typographical Errors

Verify that there are no spelling errors in the connection alias, host name, or service name in both the TNSNAMES.ORA file and the connection string.

Commands

Check TNSNAMES.ORA Location:

find $ORACLE_HOME -name tnsnames.ora

Test Connection with tnsping:

tnsping DB_ALIAS

Check Listener Status:

lsnrctl status

Set Environment Variables (Linux/Unix):

export ORACLE_HOME=/path/to/oracle_home

export TNS_ADMIN=$ORACLE_HOME/network/admin

Restart Oracle Listener (if necessary):

lsnrctl stop

lsnrctl start