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“ORA-12154: TNS: could not resolve the connect identifier specified” error while creating a linked server to Oracle

“ORA-12154: TNS: could not resolve the connect identifier specified” error while creating a linked server to Oracle

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This is one of the most common errors while creating linked server to Oracle database. Today I will discuss the reason for this error and possible resolutions.

Full error message:

OLE DB provider "MSDAORA" for linked server "LINKED_ORA" returned message "ORA-12154: TNS:could not resolve the connect identifier specified".

Msg 7303, Level 16, State 1, Line 1

Cannot initialize the data source object of OLE DB provider "MSDAORA" for linked server "LINKED_ORA".

First of all make sure you have reviewed the following Microsoft KB article that has a lot of good information on troubleshooting Oracle linked server issues.

How to set up and troubleshoot a linked server to an Oracle database in SQL Server

Also make sure you have installed Oracle Client on the SQL server. If the SQL server is 64 bit then we need to install 64 bit Oracle provider. You can also create linked server using Oracle ODBC driver together with Microsoft OLE DB provider for ODBC. Once again on a 64 bit SQL server you need to install the 64-Bit OLEDB Provider for ODBC (MSDASQL) and 64 bit Oracle ODBC drivers. However 64-Bit OLEDB Provider for ODBC (MSDASQL) is already there in Windows Vista/Windows Server 2008 and later OS.

This particular error message is a very general error message and can happen for quite a number of reasons. For general understanding of the error, you can review oracle documentation like this

In SQL Server Linked Server, it could indicate a few things (not limited to)–

1.       SQL Server (and oracle net libraries) is not able to get the TNS alias from tnsnames.ora file.

2.       Something is wrong with the way the alias is created in the tnsnames.ora file (incorrect syntax)

3.       TNS alias could not be resolved into a connect descriptor

Below is a list of things that you can try to resolve this issue.

1. Verify that the tnsnames.ora file has the alias and the service name that the customer is using.

TNS entry for the Oracle database


 OracleDB_Dev =



      (ADDRESS = (PROTOCOL = TCP)(HOST = = 1521))



      (SERVICE_NAME = OracleDB)





In the above tnsnames.ora file Alias = OracleDB_Dev

Service Name: OracleDB (Actual Oracle service name [instance name in SQL])

2.  Check the sqlnet.ora file under ‘Admin’ folder in Oracle home [Dir:\app\product\11.1.0\client_1\network\admin] and ensure that we have TNSNames in NAMES.DIRECTORY_PATH


3. Verify if you can connect to Oracle from the SQL server machine using tools installed with Oracle Client [For example "SQL Developer" or “SQL Plus”] with the same user id/password or TNS alias.

5. Check if the environment variable 'PATH' has the path for tnsnames.ora file specified.

Sample Value of Environment Variable PATH:

E:\app\product\11.1.0\client_1\bin;C:\Program Files\Business Objects\Common\3.5\bin\NOTES\;C:\Program Files\Business Objects\Common\3.5\bin\NOTES\DATA\;%Systemroot%\Microsoft.NET\Framework\v1.1.4322;%SystemRoot%\system32;%SystemRoot%;%SystemRoot%\System32\Wbem;C:\Program Files\Dell\SysMgt\oma\bin;C:\Program Files\Microsoft SQL Server\80\Tools\BINN;C:\Program Files\Common Files\Microsoft Shared\web server extensions\60\TEMPLATE\ADMIN\1033\;C:\Program Files\Microsoft SQL Server\80\Tools\Binn\;C:\Program Files\Microsoft SQL Server\90\DTS\Binn\;C:\Program Files\Microsoft SQL Server\90\Tools\binn\;C:\Program Files\Microsoft SQL Server\90\Tools\Binn\VSShell\Common7\IDE\;C:\Program Files\Microsoft Visual Studio 8\Common7\IDE\PrivateAssemblies\;C:\Program Files\Microsoft Network Monitor 3\

Note: make sure that the path is a valid path and there is no space.

6. Check the value of the key  Oracle_Home” in the registry under  HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\KEY_OraClient11g_home1  and verify that it has the right path for the Oracle home.

7.  Check for the registry key “TNS_ADMINat HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE. If it exists then make sure it has the right value as “Dir:\app\product\11.1.0\client_1\network\admin”. If you don’t see the key then create the key and set appropriate value as below.

Regedit->HKEY_LOCAL_MACHINE->Software->Oracle->RightClick NEW->StringValue and name
it TNS_ADMIN and give the value  “X:\app\product\11.1.0\client_1\network\admin”

Note: This is not a must but in some cases this is what fixed the issue.

8.   Check if SQL server start up account has permission to the Oracle Home. Also collect Process monitor log and check for “access denied”.  Process monitor log should show if we are able to find the tnsnames.ora file.

9. Make sure you don’t have multiple Oracle homes or multiple Oracle clients installed. Check the "HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\ALL_HOMES\HOME_COUNTER" key value.

10. Check if Oracle OLE DB provider is running InProcess. If ‘yes’ then try to run out-of- process and see if that resolves the issue.

Note: You can check and verify if MS OLE DB Provider for Oracle is running InProcess from the registry key at HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSSQLServer\Providers\MSDAORA

11. You can try collecting simultaneous Network trace from both SQL and Oracle servers and check if there are any communications between the two servers.

12. Try to connect to Oracle from the SQL server using the UDL.  Use the same TNS name. If you get the same error that means the issue is not specific to SSMS or linked server.

Creating and Configuring Universal Data Link (.udl) Files

13.  Try to specify all the information in the data source instead of using the TNS alias to connect to the Oracle database (this is a way to bypass tnsnames.ora file when connecting to Oracle).

Sample Data Source:


Author : Mohammad(MSFT) SQL Developer Engineer, Microsoft 

Reviewed by : Azim(MSFT), SQL Developer Technical Lead , Microsoft

Leave a Comment
  • Please add 8 and 1 and type the answer here:
  • Post
  • how to give network path while creating oracle directory.

  • This could help

  • Excellent article! Error started occurring out of a sudden. Worked on the issue on and off for four days. This article solved my issue and my code is working once more. Thank you very very much.

  • The following link has useful information,


    check environment for this error

    ORA-12154: TNS:could not resolve the connect identifier specified


  • If username/password@db is like - abc/welc@12@database. I am getting error. Since it is considering db name - 12@database. I tried giving password in double quotes. Still does't work. Please help.

  • Thanks the sample complete datasource was really helpful for connectivity.


  • How Can Write Code in Access So That Link To Specified Table In ORacle Without Using ODBC, When Give A Message 'Need Admin Permission '

    Can Someone Help Me?

  • Very helpful article. I was struggling to establish connection on my new installation and Step 7 fixed it for me.

  • Very helpful - Oracle 64-Bit on Windows 2008 64 bit

    The problem I have - the Oracle Net Manager list the 11.2.0\Client_2\Netowrk\Admin  and shows successful login under the test.

    But... The Oracle Installer was used twice as it failed because it was not installed with As Admin. It is one of the problems Oracle has. Was able to edit the TNS_Names and to get it working after a 2nd Oracle Client attempt was made.

    The Oracle De-Installer Won't work (another Oracle problem).

    My ODBC Create New Data Source shows OraClient11g_Home1 - but doesn't show OraClient11g_Home2.  

    How can I get out of this ORACLE LIMBO?

  • Hi,

    Thank you for the article. i was in trouble for around 4 days and was resolceed at last.

    Please make sure you add the Key TNS_ADMIN in the registry and create a enviroinment variable with name TNS_ADMIN and specify the correct path where the oracle is installed for Example:C:\oracle\product\32bit\\NETWORK\ADMIN.



  • Regedit->HKEY_LOCAL_MACHINE->Software->Oracle->RightClick NEW->StringValue and name

    it TNS_ADMIN and give the value  “X:\app\product\11.1.0\client_1\network\admin”

    This solved my issue.

    I was trying to connect using Entity framework with  LDAP instead of TNSNAMES

  • I am able to connect by specifyingl the information in the data source instead of using the TNS alias.

    This works great.

  • I read all the way down and when I got to #13 I knew that was the problem. Everything else had checked out. I remembered a few years ago when I was trying to create a database link with a locked down remote server and I had to do the same thing. Sometimes that is what Oracle needs and wants - the whole connection.

  • I went right to 13.  Worked beautifully...

    I wish ORACLE would get their act together on making integration with other systems easier.  

    I always groan out load (GOL?) whenever I have to deal with a new configuration/installation...

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