how to configure passwordless ssh in linux

SSH PASSWORDLESS LOGIN 

SSH (Secure Shell) is a network protocol, It also allows a user to establish a secure channel over an insecure network.
The Main difference between SSH, TELNET, RSH is security, for Telnet, rsh and rexec protocols send information, notably passwords, in plaintext.

{Note:-  ~/.ssh  is a main directory for ssh which should be present under all users home directory [~ represents the home directory of a user]. Permission for this ssh directory should be 700.}

sshd

This is the daemon service that implements the ssh server. By default it must be listening on port 22 TCP/IP [Note:- Daemon is nothing but the process that is running on the background]

Step1:- log in  as any user  on machine1 (server) and generate a pair of authentication keys. Please do not enter a passphrase

[root@server ~]# ssh-keygen

Step1:- copy the generated key from machine1(server) to machine2(client) by using this command

[root@server ~]# ssh-copy-id -i ~/.ssh/id_rsa.pub 192.168.58.129

{Note:- 192.168.58.129 is machine 2(client) IP}
Now public key file is successfully copied to machine B so you can able to login machine 2 without entering the password.

[root@server ~]# ssh 192.168.58.129
Last login: Thu Mar 19 19:20:39 2015 from 192.168.58.128
[root@client ~]#