A user’s my account allows a user to authenticate to a system and potentially to receive authorization to access resources provided by or connected to that system; however, authentication does not imply authorization. To log into an account, a user is typically required to authenticate oneself with a password or other credentials for the purposes of accounting, security, logging, and resource management.
Once the user has logged on to my account, the operating system will often use an identifier such as an integer to refer to them, rather than their username, through a process known as identity correlation. In Unix systems, the username is correlated with a user identifier or user id. Computer systems operate in one of two types based on what kind of users they have:
Single-user systems do not have a concept of several user accounts. Multi-user systems have such a concept, and require users to identify themselves before using the system. Each user account on a multi-user system typically has a home directory, in which to store files pertaining exclusively to that user’s activities, which is protected from access by other users (though a system administrator may have access). User accounts often contain a public user profile, which contains basic information provided by the account’s owner. The files stored in the home directory (and all other directories in the system) have file system permissions which are inspected by the operating system to determine which users are granted access to read or execute a file, or to store a new file in that directory.
While systems expect most user accounts to be used by only a single person, many systems have a special account intended to allow anyone to use the system, such as the username “anonymous” for anonymous FTP and the username “guest” for a guest account.