Configuring PasswordLess SSH for Apache Hadoop

In pseudo-distributed mode, we have to start daemons, and to do that, we need to have SSH installed. Hadoop doesn’t actually distinguish between pseudo-distributed and fully distributed modes: it merely starts daemons on the set of hosts in the cluster (defined by the slaves file) by SSH-ing to each host and starting a daemon process. Pseudo-distributed mode is just a special case of fully distributed mode in which the (single) host is localhost, so we need to make sure that we can SSH to localhost and log in without having to enter a password.

If you cannot ssh to localhost without a passphrase, execute the following commands:

unmesha@unmesha-hadoop-virtual-machine:~$ ssh-keygen
Generating public/private rsa key pair.
Enter file in which to save the key (/home/unmesha/.ssh/id_rsa): [press enter]
Enter passphrase (empty for no passphrase): [press enter]
Enter same passphrase again: [press enter]
Your identification has been saved in /home/unmesha/.ssh/id_rsa.
Your public key has been saved in /home/unmesha/.ssh/id_rsa.pub.
The key fingerprint is:
61:c5:33:9f:53:1e:4a:5f:e9:4d:19:87:55:46:d3:6b unmesha@unmesha-virtual-machine
The key's randomart image is:
+--[ RSA 2048]----+
|         ..    *%|
|         .+ . ++*|
|        o  = *.+o|
|       . .  = oE.|
|        S    ..  |
|                 |
|                 |
|                 |
|                 |
+-----------------+

unmesha@unmesha-hadoop-virtual-machine:~$ ssh-copy-id localhost
unmesha@localhost's password: 
Now try logging into the machine, with "ssh 'localhost'", and check in:

  ~/.ssh/authorized_keys

to make sure we haven't added extra keys that you weren't expecting.

Now you will be able to ssh without password.

unmesha@unmesha-hadoop-virtual-machine:~$ ssh localhost
Welcome to Ubuntu 12.04 LTS (GNU/Linux 3.2.0-23-generic x86_64)

 * Documentation:  https://help.ubuntu.com/

Last login: Tue Apr 29 17:48:55 2014 from amma-hp-probook-4520s.local
unmesha@unmesha-virtual-machine:~$ 

Happy Hadooping ...