This document describes how to set up and configure a single-node Hadoop installation so that you can quickly perform simple operations using Hadoop MapReduce and the Hadoop Distributed File System (HDFS).
To get a Hadoop distribution, download a recent stable release from one of the Apache Download Mirrors.
Unpack the downloaded Hadoop distribution. In the distribution, edit the file conf/hadoop-env.sh to define at least JAVA_HOME to be the root of your Java installation.
Try the following command:
$ bin/hadoop
This will display the usage documentation for the hadoop script.
Now you are ready to start your Hadoop cluster in one of the three supported modes:
By default, Hadoop is configured to run in a non-distributed mode, as a single Java process. This is useful for debugging.
The following example copies the unpacked conf directory to use as input and then finds and displays every match of the given regular expression. Output is written to the given output directory.
$ mkdir input $ cp conf/*.xml input $ bin/hadoop jar hadoop-*-examples.jar grep input output 'dfs[a-z.]+' $ cat output/*
Hadoop can also be run on a single-node in a pseudo-distributed mode where each Hadoop daemon runs in a separate Java process.
Use the following:
conf/core-site.xml:
<configuration>
<property>
<name>fs.defaultFS</name>
<value>hdfs://localhost:9000</value>
</property>
</configuration>conf/hdfs-site.xml:
<configuration>
<property>
<name>dfs.replication</name>
<value>1</value>
</property>
</configuration>conf/mapred-site.xml:
<configuration>
<property>
<name>mapred.job.tracker</name>
<value>localhost:9001</value>
</property>
</configuration>Now check that you can ssh to the localhost without a passphrase:
$ ssh localhost
If you cannot ssh to localhost without a passphrase, execute the following commands:
$ ssh-keygen -t dsa -P '' -f ~/.ssh/id_dsa $ cat ~/.ssh/id_dsa.pub >> ~/.ssh/authorized_keys
Format a new distributed-filesystem:
$ bin/hadoop namenode -format
Start the hadoop daemons:
$ bin/start-all.sh
The hadoop daemon log output is written to the $HADOOP_LOG_DIR directory (defaults to $HADOOP_PREFIX/logs).
Browse the web interface for the NameNode and the JobTracker; by default they are available at:
Copy the input files into the distributed filesystem:
$ bin/hadoop fs -put conf input
Run some of the examples provided:
$ bin/hadoop jar hadoop-*-examples.jar grep input output 'dfs[a-z.]+'
Examine the output files:
Copy the output files from the distributed filesystem to the local filesytem and examine them:
$ bin/hadoop fs -get output output $ cat output/*
or
View the output files on the distributed filesystem:
$ bin/hadoop fs -cat output/*
When you're done, stop the daemons with:
$ bin/stop-all.sh
For information on setting up fully-distributed, non-trivial clusters see Cluster Setup.
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