I'm trying to get acquainted with Linux after dealing with Windows for decades, but here's a question regarding file/directory permissions:

I have a shared directory and members of 2 groups need to access it. Group A should have read-only access, Group B should have read-write access, and Groups C+ should have no access whatsoever.

In Windows this would be a breeze to set up the group permissions accordingly. From what I understand about Linux though, I can specify one set of permissions for the owner, another set of permissions for a specified group, and then a third set of permissions for everyone else. This makes setting 3 different group access policies seemingly impossible.

What would be the best way to control access to this folder in the manner I need to do so? The folder is shared via Samba (if that provides any additional functionality).

Thanks

It's been a while since I've dived into the the samba manuals, but you can definitely set it up.

One thing you might want to setup is http://www.webmin.com/samba-howto.html which will put a web interface on your samba server / configuration.

What we did for our server was set the FS owner/permissions as follows:

drwxrwx--- 33 root DOMAIN+domain users 4096 May 8 11:22 some_folder.

Using Domain users is a safe group because everyone is in it, then limit users rights with smb.conf.

Add the following for the [share] in smb.conf

[some_folder]
comment = some_folder
path = /some_path/some_folder
create mask = 0770
directory mask = 0770
directory security mask = 0770
read list = "@DOMAIN+domain users"
write list = DOMAIN+username "@DOMAIN+Domain Admins"
valid users = "@DOMAIN+domain users"


For your group C make sure they are not in your valid users group.

Of course change your "winbind separator = +" so whatever you are using.