I don't think that su an issue on to check the existence of oratab file. BTW, did you do the install? what is the oracle version that you are looking at?. One of the things that could have happen was that who ever had installed the oracle on this system, would have not run the root.sh script. You could run that to create the oratab file. Inorder to run this you need to have su or sudoer permission on the system. It is there at
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