SSH login without password in linux

You can login to a remote Linux server without entering password using ssh-keygen.

Create public and private keys using "ssh-keygen" on local-host. ssh-keygen have two algorithm  tsa and rsa.

 root@manivel-admin:~#   ssh-keygen   -t  rsa

Generating public/private rsa key pair.

Enter file in which to save the key (/root/.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 /root/.ssh/id_rsa.

Your public key has been saved in /root/.ssh/id_rsa.pub.

The key fingerprint is:

94:94:60:5a:5f:e8:ef:7f:6d:02:3b:f9:88:39:d2:6f root@manivel-admin

The key's randomart image is:

+--[ RSA 2048]----+

|      +..o.      |

|     + ooo       |

|    .  .+        |

|       ..        |

|        S.       |

|          . .    |

|         o   + . |

|        . +oE.o o|

|         .o=++.o |

+-----------------+

root@manivel-admin:~# 

Copy the public key localhost to remote-host using "scp" command.

  root@manivel-admin:~# scp  -r  .ssh/id_rsa.pub  test@10.2.12.1:/home/test/.ssh/authorized_keys

Notes: If  .ssh directory is not there in /home/test/ .You will create .ssh

We need to set permission for .ssh directory and authorized_keys file in "Remote host".

  test@manivel:~$  chmod  755  .ssh/

  test@manivel:~$  chmod  644  .ssh/authorized_keys

Login to remote-host without entering the password

  root@manivel-admin:~#   ssh   test@10.2.12.1

                    [Note: SSH did not ask for password.]

  test@manivel:~$  [Note: You are on remote-host here]