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Hadoop Real-World Solutions Cookbook- Second Edition

You're reading from   Hadoop Real-World Solutions Cookbook- Second Edition Over 90 hands-on recipes to help you learn and master the intricacies of Apache Hadoop 2.X, YARN, Hive, Pig, Oozie, Flume, Sqoop, Apache Spark, and Mahout

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Product type Paperback
Published in Mar 2016
Publisher
ISBN-13 9781784395506
Length 290 pages
Edition 2nd Edition
Tools
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Author (1):
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Tanmay Deshpande Tanmay Deshpande
Author Profile Icon Tanmay Deshpande
Tanmay Deshpande
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Toc

Table of Contents (12) Chapters Close

Preface 1. Getting Started with Hadoop 2.X FREE CHAPTER 2. Exploring HDFS 3. Mastering Map Reduce Programs 4. Data Analysis Using Hive, Pig, and Hbase 5. Advanced Data Analysis Using Hive 6. Data Import/Export Using Sqoop and Flume 7. Automation of Hadoop Tasks Using Oozie 8. Machine Learning and Predictive Analytics Using Mahout and R 9. Integration with Apache Spark 10. Hadoop Use Cases Index

Exporting HDFS data to a local machine


In this recipe, we are going to export/copy data from HDFS to the local machine.

Getting ready

To perform this recipe, you should already have a running Hadoop cluster.

How to do it...

Performing this recipe is as simple as copying data from one folder to the other. There are a couple of ways in which you can export data from HDFS to the local machine.

  • Using the copyToLocal command, you'll get this code:

    hadoop fs -copyToLocal /mydir1/LICENSE.txt /home/ubuntu
    
  • Using the get command, you'll get this code:

    hadoop fs -get/mydir1/LICENSE.txt /home/ubuntu
    

How it works...

When you use HDFS copyToLocal or the get command, the following things occur:

  1. First of all, the client contacts NameNode because it needs a specific file in HDFS.

  2. NameNode then checks whether such a file exists in its FSImage. If the file is not present, the error code is returned to the client.

  3. If the file exists, NameNode checks the metadata for blocks and replica placements in DataNodes.

  4. NameNode...

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