Oracle Installation error: You do not have sufficient permissions to access the inventory

When I am trying to install oracle software I am getting error:
You do not have sufficient permissions to access the inventory '/u01/app/oraInventory'. Installation cannot continue. Make sure that you have read/write permissions to the inventory directory and restart the installer.: Permission denied

$ ./runInstaller
You do not have sufficient permissions to access
the inventory '/u01/app/oraInventory'. 
Installation cannot continue. 
Make sure that you have read/write permissions
to the inventory directory and restart 
the installer.: Permission denied

try to drop oraInventory and try again run installer

$ rm -rf /u01/app/oraInventory

$ ./runInstaller
You do not have sufficient permissions to access
the inventory '/u01/app/oraInventory'. 
Installation cannot continue. 
Make sure that you have read/write permissions
to the inventory directory and restart 
the installer.: Permission denied

Oracle thinks there is still a oraInventory, even I drop it.
There is a file somewhere (not in /u01) telling oracle that oraInventory exists.

It is here: /etc/oraInst.loc. After doind a few oracle installs I guessed it was in /etc, but you could use find or locate to find this file.

as root:
rm /etc/oraInst.loc

as oracle:

$ ./runInstaller
Starting Oracle Universal Installer...

Checking Temp space: must be greater than 120 MB. Actual 12603 MB Passed
Checking swap space: must be greater than 150 MB. Actual 2015 MB Passed
..

It works!