A user's 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, 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.
Password storage On
Unix systems, local user accounts are stored in the file
/etc/passwd, while user passwords may be stored at
/etc/shadow in its
hashed form. On
Microsoft Windows, user passwords can be managed within the Credential Manager program. The passwords are located in the Windows profile directory.
Username format Various computer operating-systems and applications expect/enforce different rules for the format. In
Microsoft Windows environments, for example, note the potential use of: • User Principal Name (UPN) format – for example: UserName@Example.com • Down-Level Logon Name format – for example: DOMAIN\UserName ==Terminology==