Nested POSIX groups in Linux If I want to add all of the members who belong to the supplemental group web_users to the apache group (as an additional supplemental group) can I just add web_users group to the apache group? Or do I have to recurse through the members of web_users and do a `usermod -G apache $USER` on each one?

You have to add each user independently to each group. There is no capability to add groups in a nested fashion in Unix.