Prevent Oracle DB passwords from expiring
In newer versions of Oracle DB, user passwords expire after 180 days. The user will get a warning a week before:
 ORA-28002: the password will expire within 7 days
If the password is not changed within the week, the user will be locked out:
ORA-28001: the password has expired
If the user is a human, this isn't a big problem. But if the user is another system (e.g. a web application), then the problem will propagate to the end-users, who will have no clue to what's going on.
For system users, the best solution is to prevent passwords for expiring. This can be done with the following (which will apply to all users):
ALTER PROFILE DEFAULT LIMIT PASSWORD_LIFE_TIME UNLIMITED;
If the password has already expired or is within 7 days of expiring, a little more is required: check one of the following articles:
ORA-28001: the password has expired
ORA-28002: the password will expire within 7 days
Update: Got this (relevant) comment from @hamsjaeld
It was new in Oracle 11g, that the default profile (normally used by all users except DBSNMP) expires in 180 days. Instead of simply disabling this enhanced security, it's probably better to setup appropriate profiles in the db, and assign users to them.
And, yes, the above might not be the best way to handle this, especially on production servers. For test and development servers I would think it's fine.