Oracle clients (and programs that use Oracle clients/drivers) will search for TNS configuration files such as sqlnet.ora and tnsnames.ora in the following order.
Note that the first file to be found will be used -- so if there were files in both location 3 and location 5, then the one in location 3 would be found first and used.
For UNIX systems:
- $HOME for hidden (dot) files only -- e.g. .sqlnet.ora and .tnsnames.ora
- /etc or /var/opt/oracle (depending on platform)
For Windows systems:
- Current path (associated with the running client application)
- Environment variable TNS_ADMIN defined for the user/session
- Environment variable TNS_ADMIN defined for the system
- Windows Registry Key TNS_ADMIN (beware of virtualized applications that have their own private version of the registry which you cannot view).