SUMMARY
Oracle backup fails
ISSUE
Oracle DB fails with error, PAM Authentication Error: User not known to the underlying authentication module.
RESOLUTION
On the Linux box you should be able to run:
cat /etc/oratab
This will give you a list of databases deployed on the current system. It will be a : separated list of sid:home:boot. For each unique home path you should run the following:
export ORACLE_HOME=home
${ORACLE_HOME}/bin/osdbagrp
This will give you the oradba system group used to manage the Oracle Instance. Using this group run:
lid -g group
That command should give you a list of users that could be used as system level oracle dbas for that unique home.
CAUSE
The Oracle backup needs to have a user that is known by the Linux OS and the Oracle DB. A good choice is the user that was used while installing the Oracle instance.