[Hadoop-common-user] How to debug (log4j.properties),

I am trying to debug my map/reduce (Hadoop) app with help of the logging.
When I do grep -r in $HADOOP_HOME/logs/*

There is no line with debug info found.
I need your help. What am I doing wrong?
Thanks in advance,
Tali

In my class I put :
________________________________________________________________________________
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;


LOG.warn("======");
System.out.println("====");
_________________________________________________________________________________


Here is my Log4j.properties:

log4j.rootLogger=WARN, stdout, logfile

log4j.appender.stdout=org.apache.log4j.ConsoleAppender
log4j.appender.stdout.layout=org.apache.log4j.PatternLayout
log4j.appender.stdout.layout.ConversionPattern=%d %p [%c] - <%m>%n

log4j.appender.logfile=org.apache.log4j.RollingFileAppender
log4j.appender.logfile.File=app-debug.log


#log4j.appender.logfile.MaxFileSize=512KB
# Keep three backup files.
log4j.appender.logfile.MaxBackupIndex=3
# Pattern to output: date priority [category] - message
log4j.appender.logfile.layout=org.apache.log4j.PatternLayout
log4j.appender.logfile.layout.ConversionPattern=MYLINE %d %p [%c] - %m%n
log4j.logger.org.apache.hadoop.mapred.TaskTracker=DEBUG