ERROR: OPatch failed because of Inventory problem

Error:
=====
ERROR: OPatch failed because of Inventory problem.
Cannot open the file: /etc/oraInst.loc


Please use -invPtrLoc option and specify the correct file for OPatch to look for central inventory.

Scenario:
=======

$ cd $ORACLE_HOME

$ cd OPatch
$ opatch lsinventory

Oracle Interim Patch Installer version 1.0.0.0.57
Copyright (c) 2007 Oracle Corporation. All Rights Reserved..

We recommend you refer to the OPatch documentation under
OPatch/docs for usage reference. We also recommend using
the latest OPatch version. For the latest OPatch version
and other support related issues, please refer to document
293369.1 which is viewable from metalink.oracle.com

Cannot open the file: /etc/oraInst.loc
Please use -invPtrLoc option and specify the correct file for OPatch to look for central inventory.

ERROR: OPatch failed because of Inventory problem.

Solution:
=======
$ pwd
/home/applmgr
$ find /prddb02/apps -name "*oraInst.loc"
/prod/apps/tech_st/10.1.2/oraInst.loc
/prod/apps/tech_st/10.1.3/oraInst.loc

As a root user
cp /prod/apps/tech_st/10.1.2/oraInst.loc /etc/

Now retest the issue.