How Oracle Searches for Configuration Files

Introduction
Do you have trouble finding which tnsnames.ora or listener.ora is the one on your
computer that Oracle is actually looking at? There's a few places that Oracle
looks for its configuration files (tnsnames.ora, sqlnet.ora, listener.ora, and
oratab).
Where does Oracle search for these files?
Oracle will search for these configuration files in the following locations
in the following order:

1. $TNS_ADMIN
2. /etc (or /var/opt/oracle on Solaris)
3. $ORACLE_HOME/network/admin

The TNS_ADMIN ($TNS_ADMIN in Unix/Linux and %TNS_ADMIN%
in Windows) environment variable allows you to point to any directory you wish
the files to be located at. By default the files get installed to
<ORACLE_HOME>/network/admin/.

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