hadoop入門教程

參照官網到教程做hadoop到helloword遇到些問題，把它寫在這 希望可以對大家有用
Purpose

The purpose of this document is to help you get a single-node Hadoop installation up and running very quickly so that you can get a flavour of the Hadoop Distributed File System (see
HDFS Architecture) and the Map/Reduce framework; that is, perform simple operations on HDFS and run example jobs.

Pre-requisites

Supported Platforms

• GNU/Linux is supported as a development and production platform. Hadoop has been demonstrated on GNU/Linux clusters with 2000 nodes.
• Win32 is supported as a development platform. Distributed operation has not been well tested on Win32, so it is not supported as a
  production platform.

Required Software

Required software for Linux and Windows include:

1. JavaTM 1.6.x, preferably from Sun, must be installed.
2. ssh must be installed and sshd must be running to use the Hadoop scripts that manage remote Hadoop daemons.

Additional requirements for Windows include:

1. Cygwin - Required for shell support in addition to the required software above.

Installing Software

If your cluster doesn't have the requisite software you will need to install it.

For example on Ubuntu Linux:

$ sudo apt-get install ssh
$ sudo apt-get install rsync

On Windows, if you did not install the required software when you installed cygwin, start the cygwin installer and select the packages:

• openssh - the Net category

Download

To get a Hadoop distribution, download a recent
stable release from one of the Apache Download Mirrors.

Prepare to Start the Hadoop Cluster

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:

• Local (Standalone) Mode
• Pseudo-Distributed Mode
• Fully-Distributed Mode

Standalone Operation

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/*

Pseudo-Distributed Operation

Hadoop can also be run on a single-node in a pseudo-distributed mode where each Hadoop daemon runs in a separate Java process.

Configuration

Use the following:
conf/core-site.xml:

<configuration>

<property>

<name>fs.default.name</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>

Setup passphraseless ssh

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

加上這一個命令
#service sshd start 啟動sshd到此處，有點問題，如果不起動ssh服務的話，以後會報錯服務拒絕，在往後運行就會有一系列 的錯誤。比如

（

ERROR org.apache.hadoop.mapred.TaskTracker: Caught exception: java.io.IOException: Call to localhost/127.0.0.1

）我的預設就沒啟動

Execution

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_HOME}/logs).

Browse the web interface for the NameNode and the JobTracker; by default they are available at:

• NameNode - http://localhost:50070/
• JobTracker -
  http://localhost:50030/

Copy the input files into the distributed filesystem:
$ bin/hadoop fs -put conf input

如果你沒按照我上面說到啟動ssh服務的話這裡會出錯，你把ssh啟動後再執行此步驟會有一

個目錄input已經存在到警告，換個別到目錄就可以了，比如說inputset。

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

Fully-Distributed Operation

For information on setting up fully-distributed, non-trivial clusters see
Hadoop Cluster Setup.

Java and JNI are trademarks or registered trademarks of Sun Microsystems, Inc. in the United States and other countries.

 

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http://blog.ring.idv.tw/comment.ser?i=231

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