n this tutorial I will describe the required steps for setting upa pseudo-distributed,single-node Hadoop cluster backed by theHadoop Distributed File System, running on Ubuntu Linux.
Hadoop is a framework written in Java for running applications onlarge clusters of commodity hardware and incorporates featuressimilar to those of the Google FileSystem (GFS) and ofthe MapReducecomputingparadigm. Hadoop’s HDFS isa highly fault-tolerant distributed file system and, like Hadoop ingeneral, designed to be deployed on low-cost hardware. It provideshigh throughput access to application data and is suitable forapplications that have large data sets.
The main goal of this tutorial is to get a simple Hadoopinstallation up and running so that you can play around with thesoftware and learn more about it.
This tutorial has been tested with the following softwareversions:
- UbuntuLinux 10.04 LTS (deprecated: 8.10 LTS, 8.04,7.10, 7.04)
- Hadoop 1.0.3,released May 2012
Figure 1: Cluster of machines running Hadoop at Yahoo! (Source:Yahoo!)
Prerequisites
Sun Java 6
Hadoop requires a working Java 1.5+ (aka Java 5) installation.However, using Java 1.6 (akaJava 6) is recommended for running Hadoop. Forthe sake of this tutorial, I will therefore describe theinstallation of Java 1.6.
Important Note: The apt instructions below are takenfrom
thisSuperUser.com thread. I got notified that the previousinstructions that I provided no longer work. Please be aware thatadding a third-party repository to your Ubuntu configuration isconsidered a security risk. If you do not want to proceed with theapt instructions below, feel free to install Sun JDK 6 viaalternative means (e.g. by
downloadingthe binary package from Oracle) and then continue with the nextsection in the tutorial.
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| # Add the Ferramosca Roberto's repository to your apt repositories
# See https://launchpad.net/~ferramroberto/
#
$ sudo apt-get install python-software-properties
$ sudo add-apt-repository ppa:ferramroberto/java
# Update the source list
$ sudo apt-get update
# Install Sun Java 6 JDK
$ sudo apt-get install sun-java6-jdk
# Select Sun's Java as the default on your machine.
# See 'sudo update-alternatives --config java' for more information.
#
$ sudo update-java-alternatives -s java-6-sun
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The full JDK which will be placed in /usr/lib/jvm/java-6-sun (well,this directory is actually a symlink on Ubuntu).
After installation, make a quick check whether Sun’s JDK iscorrectly set up:
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| user@ubuntu:~# java -version
java version "1.6.0_20"
Java(TM) SE Runtime Environment (build 1.6.0_20-b02)
Java HotSpot(TM) Client VM (build 16.3-b01, mixed mode, sharing)
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Adding a dedicated Hadoop system user
We will use a dedicated Hadoop user account for running Hadoop.While that’s not required it is recommended because it helps toseparate the Hadoop installation from other software applicationsand user accounts running on the same machine (think: security,permissions, backups, etc).
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| $ sudo addgroup hadoop
$ sudo adduser --ingroup hadoop hduser
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This will add the user hduser andthe group hadoop toyour local machine.
Configuring SSH
Hadoop requires SSH access to manage its nodes, i.e. remotemachines plus your local machine if you want to use Hadoop on it(which is what we want to do in this short tutorial). For oursingle-node setup of Hadoop, we therefore need to configure SSHaccess to localhost forthe hduseruserwe created in the previous section.
I assume that you have SSH up and running on your machine andconfigured it to allow SSH public key authentication. If not, thereare severalonline guides available.
First, we have to generate an SSH key forthe hduser user.
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| user@ubuntu:~$ su - hduser
hduser@ubuntu:~$ ssh-keygen -t rsa -P ""
Generating public/private rsa key pair.
Enter file in which to save the key (/home/hduser/.ssh/id_rsa):
Created directory '/home/hduser/.ssh'.
Your identification has been saved in /home/hduser/.ssh/id_rsa.
Your public key has been saved in /home/hduser/.ssh/id_rsa.pub.
The key fingerprint is:
9b:82:ea:58:b4:e0:35:d7:ff:19:66:a6:ef:ae:0e:d2 hduser@ubuntu
The key's randomart image is:
[...snipp...]
hduser@ubuntu:~$
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The second line will create an RSA key pair with an empty password.Generally, using an empty password is not recommended, but in thiscase it is needed to unlock the key without your interaction (youdon’t want to enter the passphrase every time Hadoop interacts withits nodes).
Second, you have to enable SSH access to your local machine withthis newly created key.
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| hduser@ubuntu:~$ cat $HOME/.ssh/id_rsa.pub >> $HOME/.ssh/authorized_keys
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The final step is to test the SSH setup by connecting to your localmachine with the hduser user.The step is also needed to save your local machine’s host keyfingerprint to the hduser user’s known_hosts file.If you have any special SSH configuration for your local machinelike a non-standard SSH port, you can define host-specific SSHoptions in $HOME/.ssh/config (see manssh_config for more information).
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| hduser@ubuntu:~$ ssh localhost
The authenticity of host 'localhost (::1)' can't be established.
RSA key fingerprint is d7:87:25:47:ae:02:00:eb:1d:75:4f:bb:44:f9:36:26.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added 'localhost' (RSA) to the list of known hosts.
Linux ubuntu 2.6.32-22-generic #33-Ubuntu SMP Wed Apr 28 13:27:30 UTC 2010 i686 GNU/Linux
Ubuntu 10.04 LTS
[...snipp...]
hduser@ubuntu:~$
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If the SSH connect should fail, these general tips might help:
- Enable debugging with
ssh-vvv localhost and investigate the error indetail. - Check the SSH server configuration in
/etc/ssh/sshd_config,in particular the options PubkeyAuthentication (whichshould be set to yes)and AllowUsers (ifthis option is active, add the hduser userto it). If you made any changes to the SSH server configurationfile, you can force a configuration reloadwith sudo/etc/init.d/ssh reload.
Disabling IPv6
One problem with IPv6 on Ubuntu is thatusing 0.0.0.0 forthe various networking-related Hadoop configuration options willresult in Hadoop binding to the IPv6 addresses of my Ubuntu box. Inmy case, I realized that there’s no practical point in enablingIPv6 on a box when you are not connected to any IPv6 network.Hence, I simply disabled IPv6 on my Ubuntu machine. Your mileagemay vary.
To disable IPv6 on Ubuntu 10.04 LTS,open /etc/sysctl.conf inthe editor of your choice and add the following lines to the end ofthe file:
/etc/sysctl.conf
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| # disable ipv6
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
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You have to reboot your machine in order to make the changes takeeffect.
You can check whether IPv6 is enabled on your machine with thefollowing command:
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| $ cat /proc/sys/net/ipv6/conf/all/disable_ipv6
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A return value of 0 means IPv6 is enabled, a value of 1 meansdisabled (that’s what we want).
Alternative
You can also disable IPv6 only for Hadoop as documentedin HADOOP-3437.You can do so by adding the following lineto conf/hadoop-env.sh:
conf/hadoop-env.sh
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| export HADOOP_OPTS=-Djava.net.preferIPv4Stack=true
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Hadoop
Installation
DownloadHadoop from the Apache DownloadMirrors and extract the contents of the Hadooppackage to a location of your choice. Ipicked /usr/local/hadoop.Make sure to change the owner of all the files tothe hduser userand hadoop group,for example:
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| $ cd /usr/local
$ sudo tar xzf hadoop-1.0.3.tar.gz
$ sudo mv hadoop-1.0.3 hadoop
$ sudo chown -R hduser:hadoop hadoop
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(Just to give you the idea, YMMV – personally, I create a symlinkfrom hadoop-1.0.3 to hadoop.)
Update $HOME/.bashrc
Add the following lines to the end ofthe $HOME/.bashrc fileof user hduser.If you use a shell other than bash, you should of course update itsappropriate configuration files insteadof .bashrc.
$HOME/.bashrc
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| # Set Hadoop-related environment variables
export HADOOP_HOME=/usr/local/hadoop
# Set JAVA_HOME (we will also configure JAVA_HOME directly for Hadoop later on)
export JAVA_HOME=/usr/lib/jvm/java-6-sun
# Some convenient aliases and functions for running Hadoop-related commands
unalias fs &> /dev/null
alias fs="hadoop fs"
unalias hls &> /dev/null
alias hls="fs -ls"
# If you have LZO compression enabled in your Hadoop cluster and
# compress job outputs with LZOP (not covered in this tutorial):
# Conveniently inspect an LZOP compressed file from the command
# line; run via:
#
# $ lzohead /hdfs/path/to/lzop/compressed/file.lzo
#
# Requires installed 'lzop' command.
#
lzohead () {
hadoop fs -cat $1 | lzop -dc | head -1000 | less
}
# Add Hadoop bin/ directory to PATH
export PATH=$PATH:$HADOOP_HOME/bin
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You can repeat this exercise also for other users who want to useHadoop.
Excursus: Hadoop Distributed File System (HDFS)
Before we continue let us briefly learn a bit more about Hadoop’sdistributed file system.
The Hadoop Distributed File System (HDFS) is a distributed filesystem designed to run on commodity hardware. It has manysimilarities with existing distributed file systems. However, thedifferences from other distributed file systems are significant.HDFS is highly fault-tolerant and is designed to be deployed onlow-cost hardware. HDFS provides high throughput access toapplication data and is suitable for applications that have largedata sets. HDFS relaxes a few POSIX requirements to enablestreaming access to file system data. HDFS was originally built asinfrastructure for the Apache Nutch web search engine project. HDFSis part of the Apache Hadoop project, which is part of the ApacheLucene project.
TheHadoop Distributed File System: Architecture andDesign
hadoop.apache.org/hdfs/docs/…
The following picture gives an overview of the most important HDFScomponents.
Configuration
Our goal in this tutorial is a single-node setup of Hadoop. Moreinformation of what we do in this section is available onthe HadoopWiki.
hadoop-env.sh
The only required environment variable we have to configure forHadoop in this tutorial is JAVA_HOME.Open conf/hadoop-env.sh inthe editor of your choice (if you used the installation path inthis tutorial, the full path is /usr/local/hadoop/conf/hadoop-env.sh)and set the JAVA_HOME environmentvariable to the Sun JDK/JRE 6 directory.
Change
conf/hadoop-env.sh
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| # The java implementation to use. Required.
# export JAVA_HOME=/usr/lib/j2sdk1.5-sun
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to
conf/hadoop-env.sh
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| # The java implementation to use. Required.
export JAVA_HOME=/usr/lib/jvm/java-6-sun
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Note: If you are on a Mac with OS X 10.7 you can use the followingline to set up JAVA_HOME in conf/hadoop-env.sh.
conf/hadoop-env.sh (on Mac systems)
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| # for our Mac users
export JAVA_HOME=`/usr/libexec/java_home`
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conf/*-site.xml
In this section, we will configure the directory where Hadoop willstore its data files, the network ports it listens to, etc. Oursetup will use Hadoop’s Distributed FileSystem, HDFS,even though our little “cluster” only contains our single localmachine.
You can leave the settings below “as is” with the exception ofthe hadoop.tmp.dir parameter– this parameter you must change to a directory of your choice. Wewill use the directory /app/hadoop/tmp inthis tutorial. Hadoop’s default configurationsuse hadoop.tmp.dir asthe base temporary directory both for the local file system andHDFS, so don’t be surprised if you see Hadoop creating thespecified directory automatically on HDFS at some later point.
Now we create the directory and set the required ownerships andpermissions:
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| $ sudo mkdir -p /app/hadoop/tmp
$ sudo chown hduser:hadoop /app/hadoop/tmp
# ...and if you want to tighten up security, chmod from 755 to 750...
$ sudo chmod 750 /app/hadoop/tmp
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If you forget to set the required ownerships and permissions, youwill see a java.io.IOExceptionwhenyou try to format the name node in the next section).
Add the following snippets between the ... tags in the respective configurationXML file.
In file conf/core-site.xml:
conf/core-site.xml
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hadoop.tmp.dir
/app/hadoop/tmp
A base for other temporary directories.
fs.default.name
hdfs://localhost:54310
The name of the default file system. A URI whose
scheme and authority determine the FileSystem implementation. The
uri's scheme determines the config property (fs.SCHEME.impl) naming
the FileSystem implementation class. The uri's authority is used to
determine the host, port, etc. for a filesystem.
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In file conf/mapred-site.xml:
conf/mapred-site.xml
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mapred.job.tracker
localhost:54311
The host and port that the MapReduce job tracker runs
at. If "local", then jobs are run in-process as a single map
and reduce task.
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In file conf/hdfs-site.xml:
conf/hdfs-site.xml
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dfs.replication
1
Default block replication.
The actual number of replications can be specified when the file is created.
The default is used if replication is not specified in create time.
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See GettingStarted with Hadoop and the documentationin Hadoop’sAPI Overview if you have any questions aboutHadoop’s configuration options.
单节点Hadoop集群搭建
本文详细介绍如何在Ubuntu Linux上搭建单节点伪分布式Hadoop集群，并配置Hadoop Distributed File System (HDFS)。教程覆盖了从Java安装到Hadoop配置的所有步骤。
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