seems to be a known bug.
Thanks for the reply. They gave this solution.
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What it actually means?
When the "/bin/su ..." command is run, the .profile (or .bashrc or .cshrc) of the oracle user is loaded.
If there is a menu or a prompt in the .profile (or .bashrc or .cshrc), the command will hang until we select a menu option or answer the question at the prompt. So you have to disable the prompt command in order to avoid the hang.