SSH Setup for Hadoop

Install openssh (at master and data node)
master node and datanodes install ssh using apt-get to use ssh communication.
$ sudo apt-get update sudo apt-get install openssh-server ## or sudo apt-get install
$ssh sudo ufw allow 22
Set ssh (at master node)
In the server make rsa key
$ ssh-keygen -t rsa
Make directory at datanode
$ cat $HOME/.ssh/id_rsa.pub >> $HOME/.ssh/authorized_keys
// for connection between master.
$ ssh hadoop@data01 mkdir -p .ssh
public key copy from master node to datanode

1. to its own user account on the master - i.e. ssh master in this context.
2. to the master user account on the slave via a password-less SSH login.

$ cat ~/.ssh/id_rsa.pub | ssh hadoop@data01 cat >> ~/.ssh/authorized_keys