I have received several emails asking help with why oracle does not write information into the alert log files during database startup failures.. Due to practice we tend to look for instance or database related information in our standard log directories such as $ORACLE_BASE/admin/…/bdump or $ORACLE_HOME/network/log directories. This causes panic and anxiety, searching Google, open entries on OTN forums or open an SR with Oracle support. The Oracle documentation has also not done a good job in this area.
Entries are not found in the alert log because the database/instance was not started using SQL*Plus entries are not added to the db alert log. Depending on what we are trying to look for, what area of the stack is being examined, or at what state of the application is running under, there are different kinds and flavors and locations where you could find logs.
Note: This is not a complete list, but a start for the beginners to navigate their way through the troubleshooting process.