TNS_ADMIN Environment Variable in Oracle
If you have multiple Oracle homes on a servers, I'm pretty sure that you must have multiple listener.ora file and tnsnames.ora files in their respective Oracle Homes. Is there a better way to maintain only one copy of listener.ora and tnsnames.ora files so that all Oracle Homes can refer to one location? Yes, we can achieve this using TNS_ADMIN parameter in Oracle.
Watch video TNS_ADMIN environment variable
Create TNS_ADMIN Location
First we create a directory which will act as a central location for listener.ora & tnsnames.ora. Preferably keep it outside any specific ORACLE_HOME
mkdir -p $ORACLE_BASE/network
Copy listener.ora file and tnsnames.ora file into above new folder. You may have to re-create listener.ora file to accept connections for multiple ORACLE_HOMEs.
At this stage, you can delete any listener.ora & tnsnames.ora files from all the $ORACLE_HOEM/network/admin locations
Set TNS_ADMIN Parameter
It's a good idea to set this parameter inside the .bash_profile and add below line
Great, no matter which ORACLE_HOME you are connected to, the lsnrctl utility will ready listener.ora file from TNS_ADMIN location. Also, any tns connections will be using tnsnames.ora file placed inside TNS_ADMIN location!