What should you do in case a central inventory gets lost? There are a couple of scenarios here; you could have a valid Oracle Home either intact or restored from a backup, but the central inventory is lost, if this is the case Oracle will work, but you will notice the missing inventory when you try to do an upgrade or apply a patch. In Oracle 10gR1 and earlier releases there is no other option but to restore the inventory from a backup, so you should include in your backup policies a periodic ORACLE_BASE backup which includes the different Oracle Homes and the central inventory. In Oracle 10gR2 and 11gR1, you can register it using the following procedure:

Change to the oui/bin directory inside the target Oracle Home:

cd $ORACLE_HOME/oui/bin

From this point, run the runInstaller (or setup.exe command in Windows) and use the attachHome and invPtrLoc modifiers:

./runInstaller -silent -attachHome -invPtrLoc ./oraInst.loc ORACLE_HOME="<Oracle_Home_Location>" ORACLE_HOME_NAME...