1. Automatic authentication to remote machine

Note:- with this you don't need to type password every time to do the ssh connection.

Step One—Create the RSA Key Pair (your machine)

ssh-keygen -t rsa

Step Two—Store the Keys and Passphrase (your machine)

Once you have entered the Gen Key command, you will get a few more questions:

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

You can press enter here, saving the file to the user home (in this case, my example user is called demo).

Enter passphrase (empty for no passphrase):

The entire key generation process looks like this:

ssh-keygen -t rsa

Generating public/private rsa key pair.
Enter file in which to save the key (/home/demo/.ssh/id_rsa): 
Enter passphrase (empty for no passphrase): 
Enter same passphrase again: 
Your identification has been saved in /home/demo/.ssh/id_rsa.
Your public key has been saved in /home/demo/.ssh/id_rsa.pub.
The key fingerprint is:
4a:dd:0a:c6:35:4e:3f:ed:27:38:8c:74:44:4d:93:67 demo@a
The key's randomart image is:
+--[ RSA 2048]----+
|          .oo.   |
|         .  o.E  |
|        + .  o   |
|     . = = .     |
|      = S = .    |
|     o + = +     |
|      . o + o .  |
|           . o   |
|                 |
+-----------------+

The public key is now located in /home/demo/.ssh/id_rsa.pub. The private key (identification) is now located in /home/demo/.ssh/id_rsa.

Step Three—Copy the Public Key (your machine to remote_machine)

Once the key pair is generated, it’s time to place the public key on the server that we want to use.

You can copy the public key into the new machine’s authorized_keys file with the ssh-copy-id command. Make sure to replace the example username and IP address below.

ssh-copy-id demo@198.51.100.0

2. Custom host name for ssh connection

Note:- instead of typing ``ssh user@remote.machine.ip`` you can use ``ssh host_name`` to connect easily.

First we need to modify the config file in our machine to automatically resolve the ip address of the host_name when we will ssh into it.

vim ~/.ssh/config

The general format looks like this

Host firsthost
    SSH_OPTION_1 custom_value
    SSH_OPTION_2 custom_value
    SSH_OPTION_3 custom_value

Host secondhost
    ANOTHER_OPTION custom_value

Host *host
    ANOTHER_OPTION custom_value

Host *
    CHANGE_DEFAULT custom_value

To add a new host name consider this example:

Host my_remote_machine
    HostName 192.168.0.142
    User neo

This host allows us to connect as neo@192.168.0.142 by typing this on the command line:

ssh my_remote_machine