On system boot up, one can see the login screen. We log in to the system using our user name, followed by our password. The login name is looked up in the system password file (usually /etc/passwd). If the login name is found, the password is verified. The encrypted password for a user can be seen in the file /etc/shadow, immediately preceded by the user name and a colon. Once the password is verified, we are logged into the system.