question about users and groups setup

I’m running one older server with virtualmin, and one new leaner server with just webmin.

I noticed that vitualmin makes something like creating a User, “John”, and group created named “John”. Then making john a “Primary group members” of group John, and user www-data a member also of group John.

Then even with a directory chmod 755, www-data can still write to it.

How does this work?

I tried to minic this setup with my webmin server, but i dont understand how virtualmin is doing this. There must be something like POSIX ACL in the background?


The group www-data wouldn’t be able to write to a directory that’s not group writable.

What’s likely writing to it is the user, rather than the group – in the scenario you’re describing, what user owns the file afterwards? And what user owns that directory?

The group ‘www-data’ is a member of the group ‘john’ to make sure that Apache can read static files belonging to john, such as HTML/CSS/Javascript --as those aren’t executed as the user. But that doesn’t grant Apache rights to write to those dirs.