B.1.1 In the Error Log
The Apache software does quite a reasonable job of reporting the details when it encounters problems. The reports are recorded in the server's error log, which is usually stored in one of the following places:
Where the error log is put depends upon how you installed and configured the server; the wealth of possible locations in the list above is because popular prepackaged installation kits (from Red Hat, SuSE, etc.) each has its own preferred location. Of course, the definitive location can be determined by examining your httpd.conf file for the ErrorLog directive(s).
So the very first thing you should do when Apache appears to be misbehaving is see if the server has any comments to make.
If the messages in the error log don't make the cause of the problem immediately clear, or if there aren't any messages that seem to relate to the problem, it's a good idea to crank the logging level up by changing the LogLevel setting in the httpd.conf file:
The debug setting enables all possible error messages and makes the server extremely verbose, so it's a good idea to set it back to warning or error after it has helped you locate the cause of your problem.
B.1.2 Characterize the Problem
When you're trying to diagnose a problem, here is a question you should ask yourself: "What is the current behavior, and in what ways is it different from the expected or desired behavior?"
If you ask this question, a natural successive question is, "What could cause the current behavior?"
Between the answers to these two questions often lies a "Eureka!" moment. At the very least, they narrow your area of research.