If you want to SSH login without password or automate your task between two servers, you need to setup SSH login via certificate.

This topic has detail steps on How to setup an SSH cetificate.

Step1: Generating RSA key

You login to your server and type the following command:

[root@lifelinux~]#ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa):
Created directory '/root/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
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:
a5:4c:29:3f:92:be:ee:41:03:8d:aa:59:c0:3e:f1:85 root@lifelinux

The command ssh-keygen -t rsa initiated the creation of the key pair.
No passphrase your was entered.
After this is completed, two files generated. The private key was saved in .ssh/id_rsa and public key was saved in .ssh/id_rsa.pub
Copy the public key to .ssh/authorized_keys with command:

[root@lifelinux~]#cat .ssh/id_rsa.pub >> .ssh/authorized_keys

Step2: Edit SSH config

[root@lifelinux~]#vi /etc/ssh/sshd_config

Make sure that the following settings as shown:

RSAAuthentication yes
PubkeyAuthentication yes
AuthorizedKeysFile      .ssh/authorized_keys
PasswordAuthentication no

Step3: Restart SSH service

[root@lifelinux~]#/etc/init.d/sshd restart

Please note that for Putty you will need to import the generated private key into puttygen and export it into a new private key. This is because Putty does not support the SSH generated private key.

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