Usually users don’t have access on UNIX box to modify the global TNSNAMES.ORA in the $ORACLE_HOME/network/admin. In this case all they need to do is create a .tnsnames.ora [notice the DOT before the file name] in their home directory. Next
time when you login oracle notices this file and when you try to
connect it looks up this file before the global tnsnames.ora is
referred. In case of conflicts user’s version takes precedence.
Interested read more - http://oracledoug.com/
Flag for the DBA - when a user on UNIX says he is not able to connect the culprit could be his copy of .tnsnames.ora too!
Oh I love Oracle :)
