56f1136b_Hadoop_Troubleshooting__Possible_Problem
[Symptom] You can run Hadoop jobs written in Java (like the grep example), but your HadoopStreaming jobs (such as the Python example that fetches web page titles) won't work. [Possible Solution] Use absolute paths like this from the tutorial: bin/hadoop jar contrib/hadoop-0.15.2-streaming.jar \ -mapper $HOME/proj/hadoop/multifetch.py \ -reducer $HOME/proj/hadoop/reducer.py \ -input urls/* \ -output titles [Possible Problem] 
You might have given only a relative path to the mapper and reducer programs. The tutorial originally just specified relative paths, but absolute paths are required if you are running in a real cluster.
Hadoop Troubleshooting
Possible Problem