Single Node Hadoop Installation

HADOOP INSTALLATION

This section refers to the installation settings of Hadoop on a standalone system as well as on a system existing as a node in a cluster.

SINGLE-NODE INSTALLATION

Running Hadoop on Ubuntu 

The report here will describe the required steps for setting up a single-node Hadoop cluster backed by the Hadoop Distributed File System, running on Ubuntu Linux. Hadoop is a framework written in Java for running applications on large clusters of commodity hardware and incorporates features similar to those of the Google File System (GFS) and of the MapReduce computing paradigm. Hadoop’s HDFS is a highly fault-tolerant distributed file system and, like Hadoop in general, designed to be deployed on low-cost hardware. It provides high throughput access to application data and is suitable for applications that have large data sets.

DataNode:

A DataNode stores data in the Hadoop File System. A functional file system has more than one DataNode, with the data replicated across them.

NameNode:

The NameNode is the centrepiece of an HDFS file system. It keeps the directory of all files in the file system, and tracks where across the cluster the file data is kept. It does not store the data of these file itself.

Jobtracker:

The Jobtracker is the service within hadoop that farms out MapReduce to specific nodes in the cluster, ideally the nodes that have the data, or atleast are in the same rack.

TaskTracker:

A TaskTracker is a node in the cluster that accepts tasks- Map, Reduce and Shuffle operatons – from a Job Tracker.

Secondary Namenode:

Secondary Namenode whole purpose is to have a checkpoint in HDFS. It is just a helper node for namenode

Prerequisites :

1) Java 6 JDK :

Hadoop requires a working Java 1.5+ (aka Java 5) installation.

Update the source list :-  user@ ubuntu:~$  sudo apt-get update 

OR

Install Sun Java 6 JDK  

If you already have Java JDK installed on your system, 

then you need not run the above command.

 2)  To install it   : > user@ubuntu:~$ sudo apt-get install sun-java6-jdk

The full JDK which will be placed in /usr/lib/jvm/java-6-openjdk-amd64 After installation, check whether java JDK is correctly installed or not, with the following command

   user@ubuntu:~$ java -version

3) Adding a dedicated Hadoop system user


   We will use a dedicated Hadoop user account for running Hadoop.

   user@ubuntu:~$ sudo addgroup hadoop_group
   user@ubuntu:~$ sudo adduser --ingroup hadoop_group hduser1

This will add the user hduser1 and the group hadoop_group to the local

 machine.

Add hduser1 to the sudo group

user@ubuntu:~$ sudo adduser hduser1 sudo

4) Configuring SSH

The hadoop control scripts rely on SSH to peform cluster-wide operations. For example, there is a script for stopping and starting all the daemons in the clusters. To work seamlessly, SSH needs to be setup to allow password-less login for the hadoop user from machines in the cluster. The simplest way to achive this is to generate a public/private key pair, and it will be shared across the cluster.

Hadoop requires SSH access to manage its nodes, i.e. remote machines plus your local machine. For our single-node setup of Hadoop, we therefore need to configure SSH access to localhost for the hduser user we created in the earlier.

We have to generate an SSH key for the hduser user.

user@ubuntu:~$ su – hduser1
hduser1@ubuntu:~$ ssh-keygen -t rsa -P "" 

// # P “”, here indicates an empty password 

The second line will create an RSA key pair with an empty password. 

5) You have to enable SSH access to your local machine with this newly 

created key which is done by the following command.

hduser1@ubuntu:~$cat $HOME/.ssh/id_rsa.pub >> $HOME/.ssh/authorized_keys

 6)  The final step is to test the SSH setup by connecting to the local machine with the hduser1 user. The step is also needed to save your local machine’s host key fingerprint to the hduser user’s known hosts file.

hduser@ubuntu:~$ ssh localhost

 7) Main Installation

     Now, I will start by switching to hduser

  

 hduser@ubuntu:~$ su - hduser1

 Now, download and extract Hadoop 1.2.0 

 Setup Environment Variables for Hadoop

 8) Add the following entries to .bashrc file

# Set Hadoop-related environment variables
export HADOOP_HOME=/usr/local/hadoop
# Add Hadoop bin/ directory to PATH
export PATH= $PATH:$HADOOP_HOME/bin

9) Configuration  :   hadoop-env.sh

 Change the file: conf/hadoop-env.sh

#export JAVA_HOME=/usr/lib/j2sdk1.5-sun

to in the same file

# export JAVA_HOME=/usr/lib/jvm/java-6-openjdk-amd64  (for 64 bit)
# export JAVA_HOME=/usr/lib/jvm/java-6-openjdk-amd64  (for 32 bit)

 

10 ) conf/*-site.xml

Now we create the directory and set the required ownerships and permissions
 

hduser@ubuntu:~$ sudo mkdir -p /app/hadoop/tmp
hduser@ubuntu:~$ sudo chown hduser:hadoop /app/hadoop/tmp
hduser@ubuntu:~$ sudo chmod 750 /app/hadoop/tmp

last line gives reading and writing permissions to the/app/hadoop/tmpdirectory

Error: If you forget to set the required ownerships and permissions,

you will see a java.io.IO Exception when you try to format the name node.

11)  Paste the following between <configuration>

 In file conf/core-site.xml

<property>
    <name>hadoop.tmp.dir</name>
    <value>/app/hadoop/tmp</value>
    <description>A base for other temporary directories.</description>
</property>

<property>
    <name>fs.default.name</name>
    <value>hdfs://localhost:54310</value>
    <description>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.</description>
</property>

12 ) In file conf/mapred-site.xml

• <property>
  <name>mapred.job.tracker</name>
      <value>localhost:54311</value>
      <description>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.
      </description>
  </property> 

 13) In file conf/hdfs-site.xml

• <property>
      <name>dfs.replication</name>
      <value>1</value>
      <description>Default block replication.

   The actual number of replications can be specified when the file iscreated.
   The default is used if replication is not specified in create time.
      </description>
  </property>
  

 14) Formatting the HDFS filesystem via the NameNode

To format the filesystem (which simply initializes the directory specified by the dfs.name.dir variable). Run the command

 hduser@ubuntu:~$ /usr/local/hadoop/bin/hadoop namenode –format

15) Starting your single-node cluster

 

Before starting the cluster, we need to give the required permissions to the directory with the following command

hduser@ubuntu:~$ sudo chmod -R 777 /usr/local/hadoop

Run the command

hduser@ubuntu:~$ /usr/local/hadoop/bin/start-all.sh

This will startup a Namenode, Datanode, Jobtracker and a Tasktracker on the machine.

hduser@ubuntu:/usr/local/hadoop$ jps

==================================================================

Errors:

1. If by chance your datanode is not starting, then you have to erase the contents of the folder /app/hadoop/tmp

    

   The command that can be used

   
   

   hduser@ubuntu:~:$ sudo rm –Rf /app/hadoop/tmp/*

2. You can also check with netstat if Hadoop is listening on the configured ports.

   The command that can be used

   
   

   hduser@ubuntu:~$ sudo netstat -plten | grep java

3. Errors if any, examine the log files in the /logs/ directory.

Stopping your single-node cluster

Run the command to stop all the daemons running on your machine.

hduser@ubuntu:~$ /usr/local/hadoop/bin/stop-all.sh 

========================================================

 ERROR POINTS:

If datanode is not starting, then clear the tmp folder before formatting the namenode using the following command

hduser@ubuntu:~$ rm -Rf /app/hadoop/tmp/* 

=======================Thank You ==============================