ACL

Using ACL to make an actually useable shared folder

Sadly the built in UNIX way of doing permissions, with it's notions of users, groups, and "others" is in practice quite difficult to use to make "shared folders". FACL (for file access control lists) is an extension to these mechanisms that gives more flexibility.

So, the command to Allow anyone in the users group to write files to path/to/some/folder

 setfacl -Rm g:users:rwX /path/to/some/folder/
 setfacl -d -Rm g:users:rwX /path/to/some/folder/