The operating system must know who you are in order to provide you with the correct environment. To identify yourself to the operating system, log in by entering your login name (also known as your user ID or user name) and a password. Passwords are a form of security. People who know your login name cannot log in to your system unless they know your password.
If your system is set up as a multiuser system, each authorized user will have an account, password, and login name on the system. The operating system keeps track of the resources used by each user. This is known as system accounting. Each user will be given a private area in the storage space of the system, called the file system. When you log in, the file system appears to contain only your files, although there are thousands of other files on the system.
It is possible to have more than one valid login name on a system. If you want to change from one login name to another, you do not have to log off the system. Rather, you can use the different login names simultaneously in different shells or consecutively in the same shell without logging out. In addition, if your system is part of a network with connections to other systems, you can log in to any of the other systems where you have a login name. This is referred to as a remote login.
When you have finished working on the operating system, you log off to ensure that your files and data are secure.
This section discusses the following:
Customizing the User Environment and System Information
Customizing the User Environment