Re:Stability? (Score 1)

Imagine a file that should be readable by the members of two groups, for example. No easy way in classical Unix except creating a new group with the members of them both, and you have to keep them in synch manually

It's possible to create a 3rd group and grant members of those 2 groups with `sg` and a group password (or a setuid wrapper like sudo). I doubt many people would do this, simply because the vast majority of *nix users don't seem to have heard of sg.