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Oracle Troubleshooting

ORA-03121: no interface driver connected


When trying to connect to Oracle the following error is returned:

ORA-03121: no interface driver connected – function not performed


This error indicates that Oracle does not know which database to connect to.

Possible remedies:

  • Specify the TNS alias to use as part of the connection string.
  • In order to connect to a database without specifying an explicit TNS alias (i.e. setting it 'by default') either:
    • set the environment variable ‘LOCAL’ to the required alias.
    • Set the registry value ‘HKEY_LOCAL_MACHINE\ SOFTWARE\ ORACLE\ LOCAL’ to the required alias.
  • If the workstation has not been rebooted since Oracle client was installed then try rebooting it now.

This page represents one page of many pages of notes I made whilst working with Oracle 7 through to 10i. I now no longer work with Oracle databases, but hope that these notes will continue to be of benefit to others.

About the author: is a dedicated software developer and webmaster. For his day job he develops websites and desktop applications as well as providing IT services. He moonlights as a technical author and consultant.