We did a "real" upgrade to 12c this weekend, where "real" means a production system, as opposed to my laptop, a play VM etc etc 🙂
It all went relatively smoothly except for one interesting thing, that I can’t 100% say was caused by the upgrade, but it would appear to be the case.
After the upgrade, our scheduler external jobs started failing. A quick look in the alert log revealed:
Sun Jun 29 09:26:11 2014 ORA-12012: error on auto execute of job "FIRE_SCHED_DAILY" ORA-27496: credential "LOCAL_OS_ACCT" is disabled
So its possible (not proven) that upgrading to 12c might disable credentials. In this particular case, the database went from standalone to a pluggable database.
The remedy was the simply drop and recreate the credential