If login is invoked without an argument, it asks for a user name, and, if appropriate, a password. Echoing is turned off (if possible) during the typing of the password, so it will not appear on the written record of the session.
After a successful login, accounting files are updated and the user is informed of the existence of .mail and message-of-the-day files. Login initializes the user and group IDs and the working directory, then executes a command interpreter (usually sh(I)) according to specifications found in a password file.
Login is recognized by the Shell and executed directly (without forking).