Unable to lock Central Inventory Error

When YOU encounter OPATCH error "Unable to lock Central Inventory. 

Opatch usually throw below error

"

Oracle Home : /u01/app/oraprd/product/10.2.0/db_1
Central Inventory : /u01/app/oraInventory
from : /var/opt/oracle/oraInst.loc
OPatch version : 10.2.0.3.2
OUI version : 10.2.0.3.0
OUI location : /u01/app/oraprd/product/10.2.0/db_1/oui
Log file location : /u01/app/oraprd/product/10.2.0/db_1/cfgtoollogs/opatch/opatch2007-09-22_09-50-02AM.log

Unable to lock Central Inventory. OPatch will attempt to re-lock.
Do you want to proceed? [y|n]
n
User Responded with: N
Unable to lock Central Inventory. Stop trying per user-request?
OPatchSession cannot load inventory for the given Oracle Home /u01/app/oraprd/product/10.2.0/db_1. Possible causes are:
No read or write permission to ORACLE_HOME/.patch_storage
Central Inventory is locked by another OUI instance
No read permission to Central Inventory
The lock file exists in ORACLE_HOME/.patch_storage
The Oracle Home does not exist in Central Inventory

So how do i fix this ?

You can do the follwing to fix this error.

Go to $ORACLE_HOME/.patch_stage directory see if you can directory name called 'lock' if yes remove that direcoty and re-run opatch apply command , else go to oracle central inventory directory (ex:/u01/app/oraInventory)  and see if you can find out lock directory , if yes remove this and re-rin opatch apply command.

Else

export OPATCH_DEBUG=TRUE
and then run opatch apply.

this will give you the exact phase where your patch is failing