hadoop入门教程
参照官网到教程做hadoop到helloword遇到些问题，把它写在这 希望可以对大家有用
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:
- JavaTM 1.6.x, preferably from Sun, must be installed.
- ssh must be installed and sshd must be running to use the Hadoop scripts that manage remote Hadoop daemons.
Additional requirements for Windows include:
- 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:
| |
| |
| |
conf/hdfs-site.xml:
| |
| |
| |
conf/mapred-site.xml:
| |
| |
| |
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
加上这一个命令 #service sshd start 启动sshd
到此处，有点问题，如果不起动ssh服务的话，以后会报错服务拒绝，在往后运行就会有一系列 的错误。比如
（
ERROR org.apache.hadoop.mapred.TaskTracker: Caught exception: java.io.IOException: Call to localhost/127.0.0.1
）我的默认就没启动
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
如果你没按照我上面说到启动ssh服务的话这里会出错，你把ssh启动后再执行此步骤会有一
个目录input已经存在到警告，换个别到目录就可以了，比如说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.
如果你按照官网上到教程做不对到话可以看看这个链接
http://blog.ring.idv.tw/comment.ser?i=231
博客已搬到http://marspring.mobi/