Common Hadoop Problems

Today we will learn some common problems, that a person faces while installing Hadoop. Here are few problems  listed below.

 1. Problem with ssh conguration.
 error: connection refused to port 22

2. Namenode node not reachable
    error: Retrying to connect 127.0.0.1

 1. Problem with ssh configuration: In this case you may face many kind of errors, but most common one while installing hadoop is connection refused to port 22. Here you should check if machine on which you are trying to login, should have ssh server installed.
   
If you are using Ubuntu/Lubuntu, you can install ssh server using following command.
   
   sudo apt-get install openssh-server
   
   On CentOs or Redhat you can install ssh server using yum package manager
   
   sudo yum install openssh-server
   
   after installing ssh server, make sure you have configured the keys properly and share public key with the machine that you want to login into. If the problem persists then check for configurations of ssh in your machine. you can check configuration in /etc/ssh/sshd_config file. use following command to read this file
   
   sudo gedit /etc/ssh/sshd_config
   
   In this file RSAAuthentication should be set to yes, password less authentication also should be yes.
   
   after this close the file and restart ssh with following command
   
   sudo /etc/init.d/ssh restart
   
   Now your problem should be resolved. Apart from this error you can face one more issue. Even though you have configured keys correctly, ssh is still prompting for password. In that case check if keys are being managed by ssh. For that run following command. your keys should be in 
   $HOME/.ssh folder
   
   ssh-add
   
 2. If your namenode is not reachable, first thing you should check is demons running on namnode machine. you can check that with following command

   jps
   
   This command tells you all java processes running on your machine. If you donot see Namenode in the output list, do the following. Stop the hadoop with following command.
   
   $HADOOP_HOME/bin/stop-all.sh
   
   Format the Namenode using following command
   
   $HADOOP_HOME/bin/hadoop namenode -format
   
   start hadoop with following command
   
   $HADOOP_HOME/bin/start-all.sh
   
   this time namenode should run. if you are still not able to start namenode. then check for core-site.xml file in conf directory of hadoop with following command
   
   gedit $HADOOP_HOME/conf/core-site.xml
   
   check for value for property hadoop.tmp.dir. it should be set to a path where user who is trying to run hadoop has write permissions. if you dont want to scratch your head on this set it to $HOME/hadoop_tmp directory. Now save and close this file. Format the namenode again and try starting hadoop again. Things should work this time.

    Thats all for this posts, Please share problems that you are facing, we will try to solve them together. stay tuned for more stuff :)   
   

Comments

  1. Unknown29 January 2014 at 08:46

    I too faced similar problems during my initial Hadoop installation.
    This saves a lot of time for the beginners.
    Again nice post Harjeet.

    ReplyDelete
  2. Unknown5 November 2014 at 05:42

    Thanks for InformationHadoop Course will provide the basic concepts of MapReduce applications developed using Hadoop, including a close look at framework components, use of Hadoop for a variety of data analysis tasks, and numerous examples of Hadoop in action. This course will further examine related technologies such as Hive, Pig, and Apache Accumulo. HADOOP Online Training

    ReplyDelete
  3. Poonam18 January 2016 at 04:22

    This comment has been removed by the author.

    ReplyDelete
  4. Poonam18 January 2016 at 04:24

    Hi Harjeet,

    I found your post quite informative and helpful. Could you please add some more common types of issues/problems coming while working with hadoop.

    Thanks for your posts! Keep posting :)

    ReplyDelete

Post a Comment

Popular posts from this blog

Hive UDF Example

UDF(User Defined Function) is a Very important functionality provided by Hive. It is very simple to create a UDF for Hive. In this tutorial we will learn creating UDF and how to use it with hive. There are two possible ways to create UDF. 1. using org.apache.hadoop.hive.ql.exec.UDF 2. using  org.apache.hadoop.hive.ql.udf.generic.GenericUDF        If input and output to your custom function is basic type eg. Text, FloatWritable, DoubleWritable,IntWritable etc the use  org.apache.hadoop.hive.ql.exec.UDF.        If yor input and output can be Map, set, list type of data structure the use  using  org.apache.hadoop.hive.ql.udf.generic.GenericUDF. We will discuss the first type of UDF here. I will write one more post to discuss the second approach. First of all lets assume I want to create a hive function called toUpper which will convert a string to uppercase. Follow the following steps to achieve it. 1. Download and install eclipse from  here 2. Hive should be installed, if
Read more

Custom UDF in Apache Spark

Image
Apache Spark has become very widely used framework to build Big data application. Spark SQL has made adhoc analysis on structured data very easy, So it is very popular among users who deal with huge amount of structured data. However many times you will realise that some functionality is not available in Spark SQL. For example in Spark 1.3.1 , when you are using sqlContext basic functions like variance , standard deviation and percentile are not available(You can access these using HiveContext). In a similar situation, you may like to do some string operation on an input column but functionality may not be available in sqlContext. In such situations , we can use spark udf to add new constructs in sqlContext. I have found them very handy, specially while processing string type columns. In this post we will discuss how to create UDFs in Spark and  how to use them. Use Case : Let us keep this example very simple. We will create a udf which will take a string as input and it will conve
Read more

Hadoop series : Pseudo Distributed Mode Hadoop Instalation

In this tutorial, we will learn required steps of setting up Hadoop on single node also called pseudo distributed mode. How ever as part of this series we will also setup hadoop on multiple machines. We will also learn Map Reduce, hive , Pig etc.So stay tuned, Here it comes .... :) We need Following this to start with. Ubuntu: I always prefer ubuntu as my linux flavour. However if you are using a very low end machine with very small ram, you can install Lubuntu also. Lubuntu is very light weight and any low end machine should work. If you have a windows machine. you can install hadoop using cygwin or VirtualBox or Vmware player.  Here we go... Steps for installation of Hadoop. If you are using Windows follow steps from 1 to 4 1. Download  and install Virtual box from https://www.virtualbox.org/wiki/Downloads   2. Download ubuntu from  http://www.ubuntu.com/download/desktop . If you have low  configuration machine then you can use Lubuntu. download Lubuntu from 
Read more