Understanding Users and Groups

A user account provides you with access to the Unix system, whether by a shell, an ftp account, or other means. To use the resources that the Unix system provides, you need a valid user account and resource permissions (permissions are discussed in Chapter 4). Think of your account as your passport, identifying who you are to the Unix system.

For further Mac OS X–specific information regarding users and groups, see Chapter 20.

This chapter discusses the basics of accounts and what accounts are on the various Unix systems, examines how to administer accounts, and explores the purposes of groups and how groups work. It also includes other pertinent information about users and groups in Unix.

Account Basics

There are three primary types of accounts on a Unix system: the root user (or superuser) account, system accounts, and user accounts. Almost all accounts fall into one of those categories.

Root Account

The root account's user has complete and unfettered control of the system, to the point that he can run commands to completely destroy the system. The root user (also called root) can do absolutely anything on the system, with no restrictions on files that can be accessed, removed, and modified.

The Unix methodology assumes that root users know what they want to do, so if they issue a command that will completely destroy the system, Unix allows it. If you are used to working with Microsoft Windows, its administrator account is most like Unix's root ...

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