Question

I am trying to build a collaborative filtering based Recommendation System as part of an academic project. I think Mahout project has a lot of potential and I want to use it.

I installed, Mahout, hadoop and Java on my ubuntu 10.1. Hadoop and Java have been checked to be working fine together. (Ran the Hadoop word count example job)

I am following this tutorial to run the ‘Taste Grouplens Example’ with 1 million dataset.
I typed the following

chirayu@chirayu-laptop:~/hadoop-0.20.2$ mvn -e exec:java 

-Dexec.mainClass="org.apache.mahout.cf.taste.example.grouplens.GroupLensRecommenderEvaluato

rRunner" -Dexec.args="-i /home/chirayu/mahout_source/trunk/examples/data/ratings.dat"

then i followed the running it on the hadoop cluster part of the tutorial
i did mvn install in the examples directory,it generated the jar files in examples/target/ directory,
then i proceeded to the next part where I have to run the job on hadoop
i typed in the following :

    chirayu@chirayu-laptop:~/hadoop-0.20.2$ sudo bin/hadoop jar /home/chirayu/mahout_source
/trunk/examples/target/mahout-examples-0.5-SNAPSHOT.jar 

org.apache.mahout.cf.taste.example.grouplens.GroupLensRecommenderEvaluatorRunner 

i get the following error :

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/mahout/cf/taste/eval/RecommenderEvaluator
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:247)
    at org.apache.hadoop.util.RunJar.main(RunJar.java:149)
Caused by: java.lang.ClassNotFoundException: org.apache.mahout.cf.taste.eval.RecommenderEvaluator
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:307)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
    ... 3 more

I am not too sure what to put in place of the
I am not too sure if i am deploying the jar file correctly , anybody have any ideas ?

Answer 1

Quoting my email reply to you: the GroupLens example has nothing to do with Hadoop. You should not need that at all. It looks like you’re trying to run the example via Maven, but from the Hadoop install directory. Hadoop is not Mahout so of course it can’t find Mahout classes that way. Try running from the Mahout dir.