Using Linux Groups
User accounts are great for controlling security for individual users, but they aren't so good at allowing groups of users to share resources. To accomplish this, the Linux system uses another security concept, called groups.
Group permissions allow multiple users to share a common set of permissions for an object on the system, such as a file, directory, or device (more on that later in the “Decoding File Permissions” section).
Linux distributions differ somewhat on how they handle default group memberships. Some Linux distributions create just one group that contains all the user accounts as members. You need to be careful if your Linux distribution does this, because your files may be readable by all other users on the system. Other distributions create a separate group account for each user to provide a little more security.
Each group has a unique GID, which, like UIDs, is a unique numerical value on the system. Along with the GID, each group...
