opatch lsinventory error : LsInventorySession failed: OracleHomeInventory gets null oracleHomeInfo

$ /u01/app/R12/product/11.2.0/OPatch/opatch lsinventory --invPtrLoc=/etc/oraInst.loc
Oracle Interim Patch Installer version 11.2.0.3.2
Copyright (c) 2012, Oracle Corporation.  All rights reserved.


Oracle Home       : /u01/app/R12/product/11.2.0
Central Inventory : /u01/app/R12/oraInventory
   from           : /u01/app/R12/product/11.2.0/oraInst.loc
OPatch version    : 11.2.0.3.2
OUI version       : 11.2.0.3.0
Log file location : /u01/app/R12/product/11.2.0/cfgtoollogs/opatch/opatchAM_1.log

List of Homes on this system:

Inventory load failed... OPatch cannot load inventory for the given Oracle Home.
Possible causes are:
   Oracle Home dir. path does not exist in Central Inventory
   Oracle Home is a symbolic link
   Oracle Home inventory is corrupted
LsInventorySession failed: OracleHomeInventory gets null oracleHomeInfo

OPatch failed with error code 73
$

Fix
=====

$ cd $ORACLE_HOME/oui/bin
$ ./attachHome.sh
Starting Oracle Universal Installer...

Checking swap space: must be greater than 500 MB.   Actual 2006 MB    Passed
The inventory pointer is located at /etc/oraInst.loc
The inventory is located at /u01/app/R12/oraInventory
'AttachHome' was successful.
$