Or instead of invoking mahout in format "$ hadoop jar mahout-core-0.5.jar ",
you should try "$mahout ......".
in $MAHOUT_HOME/bin, there lies the mahout script which will load all
necessary jar files before run any classes. the jars that required by
mahout are normally put in $MAHOUT_HOME/lib

e.g.

$mahout seq2sparse -i /group/tbdev/zhimo.bmz/mahout/data/vtitle_seq -o
/group/tbdev/zhimo.bmz/mahout/vectors/vtitle-vectors -ow \
-a org.apache.lucene.analysis.WhitespaceAnalyzer \
-wt tfidf \
-x 90 \
-seq \
-n 2


On Sun, Aug 26, 2012 at 10:50 PM, Sean Owen <[email protected]> wrote:

> The JAR you ship to Hadoop needs to have all the required class files
> including third-party dependencies. Right now you're just sending it
> Mahout classes. Use the ".job" file that is built by the Maven
> targets. mvn package should make them. That has all the dependencies
> packaged up.
>
> On Sun, Aug 26, 2012 at 3:32 AM, Mizrachi, Dror <[email protected]>
> wrote:
> > Hi
> >
> > I'm a new Mahout user.
> > I tried running the follow command and got this exception - any idea why
> and how to solve it?
> >
> > $ hadoop jar mahout-core-0.5.jar
> org.apache.mahout.cf.taste.hadoop.item.RecommenderJob
> -Dmapred.input.dir=/user/xxx/input -Dmapred.output.dir=/user/xxx/output
> --recommenderClassName
> org.apache.mahout.cf.taste.impl.recommender.GenericItemBasedRecommender
> --numRecommendations 10
> > Exception in thread "main" java.lang.NoClassDefFoundError:
> org/apache/commons/cli2/Option
> >         at java.lang.Class.forName0(Native Method)
> >         at java.lang.Class.forName(Class.java:247)
> >         at org.apache.hadoop.util.RunJar.main(RunJar.java:179)
> > Caused by: java.lang.ClassNotFoundException:
> org.apache.commons.cli2.Option
> >         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:306)
> >         at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
> >         ... 3 more
> >
> >
> > Thanks,
> > Dror
> >
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