From Linux machine
1. Open terminal.
2. Execute the command "ssh <username>@<ip address>".
Eg: ssh firstname.lastname@example.org
3. Enter the password for the user.
4. Execute the command 'sudo su - '.
From windows machine
1. Download putty software into the windows machine.
2. Once you have downloaded, Just click putty.exe.
3. You will get 'Basic Options for your putty session'.
-> Provide the IP address or hostname
-> provide the port number ( 22 for ssh )
-> Click 'open'.
3. A new window is opened now . Provide the following details there.
->Login as : username
4. You have logged into linux machine now.
5. Starting a session from the command line.