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How to Solve the Oracle Error ORA-12154: TNS:could not resolve the connect identifier specified

Author: Vijay Muthu | | February 4, 2021

The “ORA-12154: TNS:could not resolve the connect identifier specified” Oracle error is a commonly seen message for database administrators. When this occurs, there’s an issue with creating a connection with one of your Oracle services or database instances. In some Oracle database versions, this error may be called “ORA-12154: TNS:could not resolve service name.” The connect identifier is not able to resolve and may be caused by one or more of the following issues:

  • Inability to connect to the repository due to unplanned server and network outages
  • The entry is missing from tnsnames.ora
  • The entry in tnsnames.ora is malformed
  • The program is using tnsnames.ora from the wrong ORACLE_HOME
  • The program is not using a fully qualified service name, but no default domain is enabled in sqlnet.ora


Because there is more than one cause of the ORA-12154 error, you need to troubleshoot precisely what’s going on with your database connections. You’ll typically see this error in the Oracle client application during the connection process, not the server itself. While it can be frustrating to see this error when you’re working on an application, the fix is relatively straightforward.

Resolving ORA-12154 Error Codes

The Oracle client code uses one of three ways to look up connect data:

  • A flat file named tnsnames.ora
  • Oracle Names service
  • LDAP


When the complete ORA-12154 error appears with the text line, your program has found a working Oracle client install. However, the specified Oracle service is not listed in tnsnames.ora, Oracle Names or LDAP.

The first step in the troubleshooting process is to determine which name resolution method is deployed at your site. Most sites use tnsnames.ora, but enough use Oracle Names and LDAP, so it’s best to confirm this information.

If you are not the database administrator, get in touch with the people managing your Oracle systems and find out which method you should be using. They may be able to guide you in fixing the problem in accordance with your site’s standards.

The client code decides which mechanism to use based on the file sqlnet.ora. This file and tnsnames can usually both be found in the Oracle install directory (“ORACLE_HOME”), under network/admin/. This location may be overridden with the environment variable TNS_ADMIN.

If the sqlnet.ora file does not exist or does not specify a resolution method, then Oracle Net uses tnsnames.ora.

Example locations of Oracle networking files include:




UNIX / Linux

  • $ORACLE_HOME/network/admin/
  • /etc/
  • /var/opt/oracle/


If you fix the naming issues, but you still see the ORA-12154 error, check the Oracle service to confirm that it’s available for connections. A power outage, server failure, or network connectivity issue will make this resource inaccessible. It’s also possible that scheduled maintenance or repairs of an unrelated Oracle issue may take that resource temporarily offline.

Get Expert Help with Resolving Your ORA-12154 Errors

Datavail’s Oracle experts have an average of 15 years of experience and are well-versed in resolving common connection problems with this database technology. We offer Oracle services tailored to your needs, whether you need occasional assistance with troubleshooting or end-to-end solutions for your business.

Don’t let Oracle errors get in the way of creating high-availability, stable applications that your organization depends on. Get the most out of your technology investments by contacting us today.

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