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This article mainly shows you "how hadoop runs mapreduce tasks", which is easy to understand and well organized. I hope it can help you solve your doubts. Let me lead you to study and learn this article "how hadoop runs mapreduce tasks".

Usually my practice is to write mapper and reduce classes in eclipse, as well as driver classes, and then type jar to run on the hadoop server.

Run the task with the following command

Hadoop aboutMapReduce.MaxTemperature / opt/ncdc/micro/ output

But

If the CLASSPATH environment variable is not set or the aboutMapReduce.MaxTemperature cannot be found under CLASSPATH, an error that the class cannot find will be reported.

Error: Could not find or load main class aboutMapReduce.MaxTemperature

So what I did:

Set environment variables in / etc/profile or .bash _ profile

HADOOP_CLASSPATH=

CLASSPATH=$CLASSPATH:$HADOOP_CLASSPATH

Export HADOOP_CLASSPATH

Export CLASSPATH

But when running the above command, you should also pay attention to: the output directory should not exist, otherwise an error will be reported.

These are all the contents of the article "how hadoop runs mapreduce tasks". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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