In this recipe, we are going to export/copy data from HDFS to the local machine.
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
When you use HDFS copyToLocal
or the get
command, the following things occur:
First of all, the client contacts
NameNode
because it needs a specific file in HDFS.NameNode
then checks whether such a file exists in itsFSImage
. If the file is not present, the error code is returned to the client.If the file exists,
NameNode
checks the metadata for blocks and replica placements inDataNodes
.NameNode...