Debugging / Logging in Hadoop?

[Scott Whitecross]

I'm curious to what the best method for debugging and logging in  
Hadoop?  I put together a small cluster today and a simple application  
to process log files.  While it worked well, I had trouble trying to  
get logging information out.  Is there any way to attach a debugger,  
or get log4j to write a log file?  I tried setting up a Logger in the  
class I used for the map/reduce, but I had no luck.

Thanks.