There is one very special user account on every Unix system: the one with the user name root . This account is also called the superuser , because it has the power to override every safeguard on the system.
The root account on a Unix system has full control over every file on the system.
The root account is what is sometimes called a role account , meaning it exists to fill a role rather than being intended for a specific person to use. On some systems more than one person will be able to use the account.
On most Unix systems, you use the root account to perform system-administration tasks . In practice, this means that on those Unix systems you either log in as the root user or use the su ( switch user ) command to assume the role of the root user after having logged in with your regular account.
Mac OS X uses a slightly different approach, in which you never actually log in as root but instead use a command called sudo ( superuser do ) to perform specific commands with the power of root (see the sidebar "Why Mac OS X Uses sudo Instead of a Root Login" for a discussion of why Mac OS X does this differently). Using the sudo command is covered in Chapter 11, but you need to be aware at this point that there is a way to override any of the permission restrictions described in this chapter.