I'm new with Mac os and have few questions about the groups(I guess the question applies to unix too).

I know what Primary and Secondary groups are, but as I was reading the articles about the difference between those two, I came across with this terminology that I could not understand.

As I understand default groups are ones that are created on fresh install, but what is the difference between default and supplementary groups? Is supplementary group same as secondary groups? If not how can I differentiate that? thanks.


'Supplementary' is the traditional name for secondary groups.

'Default' groups can refer to a couple of different things:

  1. The standard groups on a regular system. On most BSD systems for example (including OS X), wheel is a default group used for administrators. In this context, it's completely orthogonal to the concept of supplementary groups.

  2. On many UNIX systems, especially Linux systems, it is common for every user to have a unique primary group with a name that matches their user name (and usually a GID that matches their UID). These groups are created by default by many tools, and are as such sometimes known as default groups.

  3. UNIX has traditionally had provisions for users to authenticate to add groups to their list of supplementary groups for permissions checks. This isn't used much these days, but when it was, the set of groups that a user is automatically a member of when they log in was sometimes called their list of default groups.

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