I finally figured out. It is in the "Definitive Guide" (2nd edition) Ch. 10 Administration/Monitoring/logging. Every daemons use the same log4j.properties file in the default $HADOOP_HOME/conf directory. However, one can change the log level dynamically in the web interface. In every daemon's web interface, (http://{taskTrackUrl}:50060, http://{dataNode}:50075, http://{jobTrackerUrl}:50030...) , put "/logLevel" in the path, e.g. http://{dataNode}:50075/logLevel, you can see the logLevel of one class and change the loglevel of some classes. Very nice feature. Too hard to find though.
Zhu, Guojun Modeling Sr Graduate 571-3824370 guojun_...@freddiemac.com Financial Engineering Freddie Mac
