Accessing Unix Server through Putty using Private Key

Type hostname or ipaddress


Then in the left side part of putty, click on SSH and expand.


Then you can see a section auth

Click on auth


There you will get a window with browse button.


Load your private key file (.ppk) and press open.

Then enter username and passphrase-key (if given) and login

This is the method we usually use to login to unix  cloud instances .


Creating a Public and Private Key using PuttyGen

On a Windows machine, you can use PuttyGen to generate a public/private key pair.

PuttyGen can be downloaded from

The private key is what you need on the client machine – for use with Putty for example. The public key goes to the host machine.

Open PuTTY Key Generator (puttygen.exe in the putty folder) which should look something like this.


PuTTYGen supports 3 key types:

  1. SSH-1 (RSA),
  2. SSH-2 RSA, and
  3. SSH-2 DSA

SSH-2 contains more features than SSH-1. SSH-1 has some design flaws which make it more vulnerable than SSH-2. Only choose SSH-1 if the server/client you want to connect to does not support SSH-2. The default SSH-2 RSA is probably better than SSH-2 DSA.

The Number of bits in a genereted key sets the size of your key, and thus the security level. For SSH-2 RSA, it’s recommended to set this at a minimum of 2048. PuTTYGen defaults to 1024. Setting this to 4096 would provide an even stronger key, but is probably overkill for most uses.


Click Generate to start the key generation. You will see something like the figure below ( move your mouse as suggested above the progress bar):


The result of the key generation is shown below. (in the box labelled Public key for pasting into OpenSSH authorized_keys file).


The Key comment enables you to generate multiple keys and easily tell them apart. It’s general recommended to set this to username@hostname, where the username is the username used for login, and hostname is, as it says on the tin, the name of the host machine. For example, for a user ‘amal’ on domain ‘’, set this to

The Key passphrase is an additional way to protect your private key, and is never transmitted over the internet. The strength of your key is not affected by the passphrase in any way. If you set one, you will be asked for it before any connection is made via SSH . Setting it might gain you a few extra moments if your key falls into the wrong hands, as the culprit tries to guess your passphrase. Obviously if your passphrase is weak, it rather defeats the purpose of having it.

If you don’t want the passphrase key, you can leave it empty.

Note that if your set a passphrase and forget it, there is no way to recover it. When you reload a previously saved private key (using the Load button), you will be asked for the passphrase if one is set.

Here is what PuTTYGen looks like after editing the key comment and the passphrase.


Now save your keys – one private and one public – using the Save private key and Save public key buttons respectively. You can save the public key in any format – *.txt is good. The private key is saved in PuTTY’s format – *.PPK. PuTTY will need this private key for authentication.



The public key in the highlighted box is all in one line as expected by OpenSSH, and is in the correct format (unlike the version you just saved). If you are using OpenSSH, this is what you paste in your .ssh/authorized_keys file.

SSH Key based access to Unix Servers

Access to Linux and Unix systems via Secure Shell (SSH) is standard practice.  It offers encrypted access to enable you to administer your server which is vital over the big bad internet.

There are different ways to access SSH: password, user keys and host-based keys.  Passwords are the most common but are less secure than key-based access.  Passwords are susceptible to keylogger attacks, as well as more likely to fool users into a “man-in-the-middle” attack (one where you think you’re logging onto your server, but you are actually proxying your connection through another server which has been compromised and is recording every keystroke and data transfer.)

Key based access is more secure as it requires two parts of a key to be present before access is granted.  When dealing with cloud based services such as Rackspace and Amazon Web Services, key based access is enabled by default.  Key based access is also known as “passwordless access” as access is granted by your key, not by asking for any passwords.  The exception to this is if you put a password on your key (but you can enable services that ask for this password once and it is cached for the rest of your session).

Setting this up on your Linux server is very simple, and most installations of SSH (OpenSSH) enable both password and key-based access by default.  Let’s assume user@client needs to access user@server

Ensure OpenSSH is installed on your Linux server (server)


sudo apt-get install openssh-server

CentOS/Fedora/RedHat/Oracle Enterprise Linux

sudo yum install openssh-server

Ensure the following lines has been uncommented from /etc/ssh/sshd_config

RSAAuthentication yes
PubkeyAuthentication yes

Restart OpenSSH


sudo /etc/init.d/ssh restart

CentOS/Fedora/RedHat/Oracle Enterprise Linux

sudo /etc/init.d/sshd restart

On your Linux client (desktop or other server you’ll be using to connect to the server configured in steps 1-3)

Generate your public and private keys

ssh-keygen -t rsa

You will see output like the following:

Generating public/private rsa key pair.
Enter file in which to save the key (/home/user/.ssh/id_rsa):
Created directory ‘/home/user/.ssh’.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/user/.ssh/id_rsa.
Your public key has been saved in /home/user/.ssh/
The key fingerprint is:
79:e1:08:77:c2:0d:c4:ff:35:22:64:9a:4d:03:b8:67 user@client
The key’s randomart image is:
+–[ RSA 2048]—-+
|       ++.                      |
|      …o=                    |
|      ..+O+.                 |
|      .oE*+.. o             |
|       oS oo o .            |
|         .  .                     |
|                                  |
|                                  |
|                                  |

This produces two important pieces of data.  Your PRIVATE KEY (~/.ssh/id_rsa) and your PUBLIC KEY (~/.ssh/  You must keep your PRIVATE KEY safe.  Your public key can be given to anyone.  Without your private key your public key is just a string of characters and you can’t generate a private key from a public key.  Equally, you can’t generate a public key from a private key.  Together they make your key-pair.
To enable your private key to access the server running SSH configured in steps 1-3 (server) you simply copy the contents of your public key onto the server.
Copy the public key from your client machine to server

scp .ssh/ user@server:
(enter your password)

Login to server

ssh user@server
(enter your password)

Copy the public key to authorized_keys

cat .ssh/ >> .ssh/authorized_keys

Change the permission of authorized_keys file to 600 (rw——-)

chmod 0600 .ssh/authorized_keys

This creates the directory .ssh/ and relevant authorized_keys file with the correct permissions (anything less strict will not work).  You can put in a number of public keys in here, line-by-line.  When there are multiple entries it allows multiple people to connect to that account using their keys.  This becomes useful when a team of system administrators require access to systems with minimal accounts installed, but each are accountable for audit purposes as to who logged onto the system.

Log out of that session and log back in again and you shouldn’t be asked for a password.

Hadoop FS Shell Commands

FS Shell

FS shell means FileSystem shell. The file system may be hdfs or the local file system(linux file system.

For HDFS the scheme is hdfs,

Eg: hdfs://namenodehost:<port>/user/test

For the local filesystem the scheme is file.

Eg: file:///testfile

If no schema is specified, the default scheme specified in the configuration is used. By default it is hdfs.

Majority of the commands in FS shell behave like corresponding Unix commands. Differences are described with each of the commands.


Usage: hadoop fs -cat URI [URI …]

Copies source paths to stdout.


  • hadoop fs -cat hdfs:// hdfs://
  • hadoop fs -cat file:///file3 /user/hadoop/file4

Exit Code:
Returns 0 on success and -1 on error.


Usage: hadoop fs -chgrp [-R] GROUP URI [URI …]

Change group association of files. With -R, make the change recursively through the directory structure. The user must be the owner of files, or else a super-user. Additional information is in the HDFS Admin Guide: Permissions.


Usage: hadoop fs -chmod [-R] <MODE[,MODE]… | OCTALMODE> URI [URI …]

Change the permissions of files. With -R, make the change recursively through the directory structure. The user must be the owner of the file, or else a super-user. Additional information is in the HDFS Admin Guide: Permissions.


Usage: hadoop fs -chown [-R] [OWNER][:[GROUP]] URI [URI ]

Change the owner of files. With -R, make the change recursively through the directory structure. The user must be a super-user. Additional information is in the HDFS Admin Guide: Permissions.


Usage: hadoop fs -copyFromLocal <localsrc> URI

Similar to put command, except that the source is restricted to a local file reference.


Usage: hadoop fs -copyToLocal [-ignorecrc] [-crc] URI <localdst>

Similar to get command, except that the destination is restricted to a local file reference.


Usage: hadoop fs -count [-q] <paths>

Count the number of directories, files and bytes under the paths that match the specified file pattern. The output columns are:

The output columns with -q are:


  • hadoop fs -count hdfs:// hdfs://
  • hadoop fs -count -q hdfs://

Exit Code:

Returns 0 on success and -1 on error.


Usage: hadoop fs -cp URI [URI …] <dest>

Copy files from source to destination. This command allows multiple sources as well in which case the destination must be a directory.

  • hadoop fs -cp /user/hadoop/file1 /user/hadoop/file2
  • hadoop fs -cp /user/hadoop/file1 /user/hadoop/file2 /user/hadoop/dir

Exit Code:

Returns 0 on success and -1 on error.


Usage: hadoop fs -du URI [URI …]

Displays aggregate length of files contained in the directory or the length of a file in case its just a file.
hadoop fs -du /user/hadoop/dir1 /user/hadoop/file1 hdfs://
Exit Code:
Returns 0 on success and -1 on error.


Usage: hadoop fs -dus <args>

Displays a summary of file lengths.


Usage: hadoop fs -expunge

Empty the Trash. Refer to HDFS Architecture for more information on Trash feature.


Usage: hadoop fs -get [-ignorecrc] [-crc] <src> <localdst>

Copy files to the local file system. Files that fail the CRC check may be copied with the -ignorecrc option. Files and CRCs may be copied using the -crc option.


  • hadoop fs -get /user/hadoop/file localfile
  • hadoop fs -get hdfs:// localfile

Exit Code:

Returns 0 on success and -1 on error.


Usage: hadoop fs -getmerge <src> <localdst> [addnl]

Takes a source directory and a destination file as input and concatenates files in src into the destination local file. Optionally addnl can be set to enable adding a newline character at the end of each file.


Usage: hadoop fs -ls <args>

For a file returns stat on the file with the following format:
filename <number of replicas> filesize modification_date modification_time permissions userid groupid
For a directory it returns list of its direct children as in unix. A directory is listed as:
dirname <dir> modification_time modification_time permissions userid groupid
hadoop fs -ls /user/hadoop/file1 /user/hadoop/file2 hdfs:// /nonexistentfile
Exit Code:
Returns 0 on success and -1 on error.


Usage: hadoop fs -lsr <args>
Recursive version of ls. Similar to Unix ls -R.


Usage: hadoop fs -mkdir <paths>

Takes path uri’s as argument and creates directories. The behavior is much like unix mkdir -p creating parent directories along the path.


  • hadoop fs -mkdir /user/hadoop/dir1 /user/hadoop/dir2
  • hadoop fs -mkdir hdfs:// hdfs://

Exit Code:

Returns 0 on success and -1 on error.


Usage: dfs -moveFromLocal <localsrc> <dst>

Similar to put command, except that the source localsrc is deleted after it’s copied.


Usage: hadoop fs -moveToLocal [-crc] <src> <dst>

Displays a “Not implemented yet” message.


Usage: hadoop fs -mv URI [URI …] <dest>

Moves files from source to destination. This command allows multiple sources as well in which case the destination needs to be a directory. Moving files across filesystems is not permitted.

  • hadoop fs -mv /user/hadoop/file1 /user/hadoop/file2
  • hadoop fs -mv hdfs:// hdfs:// hdfs:// hdfs://

Exit Code:

Returns 0 on success and -1 on error.


Usage: hadoop fs -put <localsrc> … <dst>

Copy single src, or multiple srcs from local file system to the destination filesystem. Also reads input from stdin and writes to destination filesystem.

  • hadoop fs -put localfile /user/hadoop/hadoopfile
  • hadoop fs -put localfile1 localfile2 /user/hadoop/hadoopdir
  • hadoop fs -put localfile hdfs://
  • hadoop fs -put – hdfs://
    Reads the input from stdin.

Exit Code:

Returns 0 on success and -1 on error.


Usage: hadoop fs -rm URI [URI …]

Delete files specified as args. Only deletes non empty directory and files. Refer to rmr for recursive deletes.

  • hadoop fs -rm hdfs:// /user/hadoop/emptydir

Exit Code:

Returns 0 on success and -1 on error.


Usage: hadoop fs -rmr URI [URI …]

Recursive version of delete.

  • hadoop fs -rmr /user/hadoop/dir
  • hadoop fs -rmr hdfs://

Exit Code:

Returns 0 on success and -1 on error.


Usage: hadoop fs -setrep [-R] <path>

Changes the replication factor of a file. -R option is for recursively increasing the replication factor of files within a directory.


  • hadoop fs -setrep -w 3 -R /user/hadoop/dir1

Exit Code:

Returns 0 on success and -1 on error.


Usage: hadoop fs -stat URI [URI …]

Returns the stat information on the path.


  • hadoop fs -stat path

Exit Code:
Returns 0 on success and -1 on error.


Usage: hadoop fs -tail [-f] URI

Displays last kilobyte of the file to stdout. -f option can be used as in Unix.


  • hadoop fs -tail pathname

Exit Code:
Returns 0 on success and -1 on error.


Usage: hadoop fs -test -[ezd] URI

-e check to see if the file exists. Return 0 if true.
-z check to see if the file is zero length. Return 0 if true
-d check return 1 if the path is directory else return 0.


  • hadoop fs -test -e filename


Usage: hadoop fs -text <src>

Takes a source file and outputs the file in text format. The allowed formats are zip and TextRecordInputStream.


Usage: hadoop fs -touchz URI [URI …]

Create a file of zero length.


  • hadoop -touchz pathname

Exit Code:
Returns 0 on success and -1 on error.

Hadoop Versions

Apache Hadoop Versions

Hadoop Versions

Hadoop 2.0.3-alpha (released on 14 February, 2013) 2.X.X – current alpha version
Hadoop 2.0.2-alpha (released on 9 October, 2012)
Hadoop 2.0.1-alpha (released on 26 July, 2012)
Hadoop 2.0.0-alpha (released on 23 May, 2012)

Hadoop 1.1.2 (released on 15 February, 2013) 1.1.X – current beta version
Hadoop 1.1.1 (released on 1 December, 2012)
Hadoop 1.1.0 (released on 13 October, 2012)
Hadoop 1.0.4 (released on 12 October, 2012) 1.0.X – current stable version
Hadoop 1.0.3 (released on 16 May, 2012)
Hadoop 1.0.2 (released on 3 Apr, 2012)
Hadoop 1.0.1 (released on 10 Mar, 2012)
Hadoop 1.0.0 (released on 27 December, 2011)

Hadoop 0.23.6 (released on 7 February, 2013) 0.23.X – simmilar to 2.X.X but missing NN HA
Hadoop 0.23.5 (released on 28 November, 2012)
Hadoop 0.23.4 (released on 15 October, 2012)
Hadoop 0.23.3 (released on 17 September, 2012)
Hadoop 0.23.1 (released on 27 Feb, 2012)
Hadoop 0.22.0 (released on 10 December, 2011) 0.22.X – does not include security
Hadoop 0.23.0 (released on 11 Nov, 2011)
Hadoop (released on 17 Oct, 2011)
Hadoop (released on 5 Sep, 2011)
Hadoop (released on 11 May, 2011) 0.20.203.X – old legacy stable version
Hadoop 0.21.0 (released on 23 August, 2010)
Hadoop 0.20.2 (released on 26 February, 2010) 0.20.X – old legacy version
Hadoop 0.20.1 (released on 14 September, 2009)
Hadoop 0.19.2 (released on 23 July, 2009)
Hadoop 0.20.0 (released on 22 April, 2009)
Hadoop 0.19.1 (released on 24 February, 2009)
Hadoop 0.18.3 (released on 29 January, 2009)
Hadoop 0.19.0 (released on 21 November, 2008)
Hadoop 0.18.2 (released on 3 November, 2008)
Hadoop 0.18.1 (released on 17 September, 2008)
Hadoop 0.18.0 (released on 22 August, 2008)
Hadoop 0.17.2 (released on 19 August, 2008)
Hadoop 0.17.1 (released on 23 June, 2008)
Hadoop 0.17.0 (released on 20 May, 2008)
Hadoop 0.16.4 (released on 5 May, 2008)
Hadoop 0.16.3 (released on 16 April, 2008)
Hadoop 0.16.2 (released on 2 April, 2008)
Hadoop 0.16.1 (released on 13 March, 2008)
Hadoop 0.16.0 (released on 7 February, 2008)
Hadoop 0.15.3 (released on 18 January, 2008)
Hadoop 0.15.2 (released on 2 January, 2008)
Hadoop 0.15.1 (released on 27 November, 2007)
Hadoop 0.14.4 (released on 26 November, 2007)
Hadoop 0.15.0 (released on 29 October 2007)
Hadoop 0.14.3 (released on 19 October, 2007)
Hadoop 0.14.1 (released on 4 September, 2007)

Hadoop Distributions

Below are the companies offering commercial implementations and/or providing support for Apache Hadoop, which is the base for all the below.

  • Cloudera offers CDH (Cloudera’s Distribution including Apache Hadoop) and Cloudera Enterprise.
  • Hortonworks (formed by Yahoo and Benchmark Capital), whose focus is on making Hadoop more robust and easier to install, manage and use for enterprise users. Hortonworks provides Hortonworks Data Platform (HDP).
  • MapR Technologies offers distributed filesystem and MapReduce engine, the MapR Distribution for Apache Hadoop.
  • Oracle announced the Big Data Appliance, which integrates Cloudera’s Distribution Including Apache Hadoop (CDH).
  • IBM offers InfoSphere BigInsights based on Hadoop in both a basic and enterprise edition.
  • Greenplum, A Division of EMC, offers Hadoop in Community and Enterprise editions.
  • Intel – the Intel Distribution for Apache Hadoop is the product includes the Intel Manager for Apache Hadoop for managing a cluster.
  • Amazon Web Services – Amazon offers a version of Apache Hadoop on their EC2 infrastructure, sold as Amazon Elastic MapReduce.
  • VMware – Initiate Open Source project and product to enable easily and efficiently deploy and use Hadoop on virtual infrastructure.
  • Bigtop – project for the development of packaging and tests of the Apache Hadoop ecosystem.
  • DataStax – DataStax provides a product of Hadoop which fully integrates Apache Hadoop with Apache Cassandra and Apache Solr in its DataStax Enterprise platform.
  • Cascading – A popular feature-rich API for defining and executing complex and fault tolerant data processingworkflows on a Apache Hadoop cluster.
  • Mahout – Apache project using Hadoop to build scalable machine learning algorithms like canopy clustering, k-means and many more.
  • Cloudspace – uses Apache Hadoop to scale client and internal projects on Amazon’s EC2 and bare metal architectures.
  • Datameer – Datameer Analytics Solution (DAS) is a Hadoop-based solution for big data analytics that includes data source integration, storage, an analytics engine and visualization.
  • Data Mine Lab – Developing solutions based on Hadoop, Mahout, HBase and Amazon Web Services.
  • BigDataEdge (Infosys) – An Insight creation product which contains hundreds of components to get accurate insights with no pains.
  • Debian – A Debian package of Apache Hadoop is available.
  • HStreaming – offers real-time stream processing and continuous advanced analytics built into Hadoop, available as free community edition, enterprise edition, and cloud service.
  • Impetus
  • Karmasphere – Distributes Karmasphere Studio for Hadoop, which allows cross-version development and management of Apache Hadoop jobs.
  • Nutch – Apache Nutch, flexible web search engine software.
  • NGDATA – Makes available Lily Open Source that builds upon Hadoop, HBase and SOLR. Distributes Lily Enterprise.
  • Pentaho – Pentaho provides a complete, end-to-end open-source BI and offers an easy-to-use, graphical ETL tool that is integrated with Apache Hadoop for managing data and coordinating Hadoop related tasks in the broader context of ETL and Business Intelligence workflow.
  • Pervasive Software – Provides Pervasive DataRush, a parallel dataflow framework which improvesperformance of Apache Hadoop and MapReduce jobs by exploiting fine-grained parallelism on multicore servers.
  • Platform Computing – Provides an Enterprise Class MapReduce solution for Big Data Analytics with high scalability and fault tolerance. Platform MapReduce provides unique scheduling capabilities and its architecture is based on almost two decades of distributed computing research and development.
  • Sematext International – Provides consulting services around Apache Hadoop and Apache HBase, along with large-scale search using Apache Lucene, Apache Solr, and Elastic Search.
  • Talend – Talend Platform for Big Data includes support and management tools for all the major Apache Hadoop distributions. Talend Open Studio for Big Data is an Apache License Eclipse IDE, which provides a set of graphical components for HDFS, HBase, Pig, Sqoop and Hive.
  • Think Big Analytics – Offers expert consulting services specializing in Apache Hadoop, MapReduce and relateddata processing architectures.
  • Tresata – Financial Industry’s first software platform architected from the ground up on Hadoop. Data storage, processing, analytics and visualization all done on Hadoop.
  • WANdisco is a committed member & sponsor of the Apache Software community and has active committers on several projects including Apache Hadoop.