Mac OS X Tiger in a Nutshell

Owners and Groups

Now, who gets these permissions? To allow people to work together, Unix has three levels of permission: owner, group, and other. The other covers everybody who has access to the system and who isn’t the owner or a member of the group.

The idea behind having groups is to give a set of users, such as a team of programmers, access to a file or set of applications. For instance, a programmer creating source code may reserve write permission to himself, but allow members of his group to have read access through a group permission. As for other, it might have no permission at all.

Each file has an owner and a group. The owner is generally the user who created the file. Each user also belongs to a default group that has the same name as the user account, if that account was created in Tiger (older versions of Mac OS X assigned the group staff to new accounts). Therefore, by default, each user is the only member or their group. That group, then, is assigned to every file the user creates. You can create other groups, though, and assign each user to multiple groups. By changing the group assigned to a file, you can give this level of access to any collection of people you want.

Mac OS 9 had something similar to this system with its Users & Groups Control panel, but this was relevant mainly to configuring who could mount your machine’s hard drive over a network. Mac OS X’s permission system also applies itself to this use but is far more pervasive, affecting every user’s interaction ...