Problem while executing hadoop code

Question

I just started with Hadoop. I wrote a sample hadoop code as was written in the book. But still, during the time of execution exceptions arise. The snippet of what I get :

[harsh@geek hadoop-0.20.2]$ hadoop MaxTemperature input/ncdc/sample.txt output Exception in thread "main" java.lang.NoClassDefFoundError: MaxTemperature Caused by: java.lang.ClassNotFoundException: MaxTemperature at java.net.URLClassLoader$1.run(URLClassLoader.java:202) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:190) at java.lang.ClassLoader.loadClass(ClassLoader.java:307) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:248) Could not find the main class: MaxTemperature. Program will exit.

What shall I do?

did you compile your code with a compiler (javac)?

KARASZI István
– KARASZI István

2010-09-28 22:17:00 +00:00
Commented Sep 28, 2010 at 22:17 — KARASZI István
– KARASZI István, Commented Sep 28, 2010 at 22:17

Joe Stein · Accepted Answer · 2010-09-29 00:32:45Z

0

When you run a hadoop jar this is the command which you should run in the directory you put the jar in (e.g. /usr/lib/hadoop-0.20/bin )

hadoop jar NAMEOFJAR.jar arg1 arg2 argN

from your question this could be how to run it (make the cd to hadoop directory for the version of hadoop your running)

cp MaxTemperature.jar /usr/lib/hadoop-0.20/bin
su hadoop
cd /usr/lib/hadoop-0.20/bin
hadoop jar MaxTemperature.jar input/ncdc/sample.txt output

answered Sep 29, 2010 at 0:32

Joe Stein

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2 Comments

Harsh Over a year ago

does that mean that I have to create a jar file for my code? the book also said this but it was written in the way as if it were just an option. and if I have to, how do I make one?

coffeepac Over a year ago

you do have to make a jar file. if you're using eclipse, there's an option for it. a tutorial shouldn't be hard to find.

Woot4Moo · Accepted Answer · 2010-09-28 19:58:36Z

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Add the MaxTemperature class to your class path.

answered Sep 28, 2010 at 19:58

Woot4Moo

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5 Comments

Harsh Over a year ago

I tried it. It still didn't work. "set CLASSPATH=/home/harsh/hadoop/hadoop-0.20.2/MaxTemp.java "

Harsh Over a year ago

or probably you asked me to do something else? because I am totally new to Hadoop as I mentioned in the post.

Woot4Moo Over a year ago

I was under the impression it would work much the same as the java classpath issues that resemble this problem, based on your tags.

Harsh Over a year ago

my bad! the book also says about setting classpath. "export HADOOP_CLASSPATH=build/classes" I did even this but still I get the same error.

Harsh Over a year ago

I am doing this through command line and i have been stuck for almost a day now with this.

RFT · Accepted Answer · 2011-12-08 19:17:25Z

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It always looks for the entry point which is the main class, the piece of code which sets your mapper and reducer class. If it cant find it, it throws classnotfound exception.

answered Dec 8, 2011 at 19:17

RFT

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Bajingan Keparat · Accepted Answer · 2012-05-18 12:25:35Z

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I experienced the same thing. I documented a step by step solution on http://digitallibraryworld.com/?p=256. Hope it helps someone

answered May 18, 2012 at 12:25

Bajingan Keparat

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1 Comment

Lix Over a year ago

Whilst this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference.

Mad Echet · Accepted Answer · 2013-02-24 21:48:02Z

0

Did you put MaxTemperature in a package?

If so, say your MaxTemperature.class file is in yourdir/bin/yourpackage/. You need to do:

export HADOOP_CLASSPATH=yourdir/bin
hadoop yourpackage.MaxTemperature

answered Feb 24, 2013 at 21:48

Mad Echet

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LakshmiNarayana · Accepted Answer · 2014-02-21 09:53:45Z

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For Map Reduce Execution first you need to create Jar file with the classes i.e. Mapper,Reducer,Driver class. Move to folder where jar file is located and execute

bin/hadoop Sample.jar SampleDriver InputFileName OutPutFileName

Try it. should Work with these flow.

answered Feb 21, 2014 at 9:53

LakshmiNarayana

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