> 1) Members of the "administrators" group have unlimited read/write > access to /home/pub and below. > > 2) Members of the "agents" group have read-only access to /home/pub and > below. > > 3) All the others (that is, members of neither "administrators" and > "agents") have no access at all to /home/pub, not even for listing the > directory content. > > The thing is: I can't seem to formulate my problem in terms of > user/group/others, as there are no owners, but two distinct groups > involved. > > Any idea how to crack that nut? Have you looked at using ACLs? Just make sure that any backup software you use can handle them.