How to setup SSH keys ?

Create the key pair on the client machine

ssh-keygen -t rsa

Enter file in which to save the key (/home/shaan/.ssh/id_rsa):

Enter passphrase (empty for no passphrase):

Public key will be located in /home/shaan/.ssh/id_rsa.pub 
Private key will be located in /home/shaan/.ssh/id_rsa

Copy the Public Key to server
Copy the public key into the server's authorized_keys file with the ssh-copy-id command : 
ssh-copy-id user@host_or_ip

or series of commands : 

• Copy the contents of ~/.ssh/id_rsa.pub into the file ~/.ssh/authorized_keys on the machine to which you want to connect.

• If the file ~/.ssh/authorized_keys exists , append the contents of the file ~/.ssh/id_rsa.pub to the file ~/.ssh/authorized_keys on the other machine.
         

cat ~/.ssh/id_rsa.pub | ssh user@host_or_ip "mkdir -p ~/.ssh && cat >>  ~/.ssh/authorized_keys"



Put the changes into effect by :
Restart SSH service

TROUBLESHOOTING

Check on local and remote servers, if OpenSSH is running 

ssh -V

Check and set permissions of .ssh directory on remote server
chmod 755 ~/.ssh
chmod 644 ~/.ssh/authorized_keys


Check and start the SSH Agent on local server, if not running
ps -ef | grep ssh-agent
ssh-agent $SHELL


Check SSH login to remote server from local
ssh -l username remote_host