Tomcat: The Definitive Guide, 2nd Edition

Chapter 8. Debugging and Troubleshooting

Troubleshooting application servers can be intimidating. In this chapter, we show you some ways to look for information that will help you to find out why things aren't working and give you examples of mistakes we and others have made where it was not immediately obvious where the error occurred. We also discuss why Tomcat may not shut down gracefully and what you can do about this common problem, as well as ways of preventing abnormal shutdowns from recurring.

Reading Logfiles

Tomcat's logging is quite configurable and a great help in diagnosing problems. Virtually every object in Tomcat's container system has a configurable log level that may be set in conf/logging.properties. Set the log level to the verbosity you would like and restart Tomcat.

If you're having problems with Tomcat and you're not seeing any hints in the logfiles, it's probably a good idea to turn up some of the logging levels and try again. First, make a backup copy of your logging.properties file:

# cd $CATALINA_HOME/conf
# cp logging.properties logging.properties.stock

Then, edit your logging.properties file. It's probably a good idea to change logging levels one at a time because you can easily end up getting too much logging information. Set one of the log levels higher, restart Tomcat, and try to reproduce your problem. Then, look at the logfiles again. If you still don't see any hints about your problem, go back and change another element's log level. Repeat this process ...