Groups

Each account is assigned membership in a group when it is created. Privileges assigned to a group are available to all accounts in the group. An account can belong to more than one group at a time.

Groups are a useful way to grant privileges to an account. For instance, suppose you have a program, called destroy, that only certain people should use. You can set up this program so it's available for use by people in the expert group, but not by all users. When you install a new account that needs to run the destroy program, you assign the account to the expert group. If you install a new program, destroy2, for the use of this group of people, you set up the new program so that only the expert group can run it.

At least one group must be assigned to each account when it's created. A group must exist before any account can be assigned to it. Linux allows you to set a system default group that is assigned to each new account. Some Linux systems assign the same group, usually named users, to all new accounts. The user group has no extraordinary privileges. Other Linux systems assign an individual group to each new account. For instance, when Fedora creates a user account, it also creates a group with the same name and assigns the group to the new account. Thus, the account janet belongs to the group janet. The group janet has no extra privileges.

Linux installs several groups by default. Root is one group installed by Linux; the root account is a member of the root group. If a new account is assigned to the root group, the new account will have the same privileges that are assigned to root.

You can create groups for your own purposes. Group names should represent the purpose of the group, such as the sales group or the mail group. Group names are limited to 16 or fewer characters.

Groups allow privileges to accounts by means of file permissions. File permissions are discussed in Chapter 9.