MacOS – Sharing common folder in OS Mavericks and on Windows 8

You have just identified why directories were invented to allow one server to define for a group of computers what users belong to which groups so that when sharing files, the permissions match so that computer Y will see the restrictions hosted from computer Z properly.

The first step is to decide how and where you will enforce the mapping of users to groups so that you can then set up sharing in a way that will work for you.

You'll want to decide if unix permissions (number based users and groups) is workable or if you need real ACL. Nothing prevents you from setting up each computer to mirror the others, but this doesn't scale well as you add people and computers.

The default permissions for newly created (/copied) items allow read and write access only to the owner (whoever created it), read-only access to everyone else. The best way around this is to create an access control entry on the folder, and set it to be inherited to items created in (/copied into) it. 'Course, the Finder doesn't give you access to the inheritance controls, so you have to go to the command line:

chmod +a "group:staff allow list,add_file,search,delete,add_subdirectory,delete_child,readattr,writeattr,readextattr,writeextattr,readsecurity,writesecurity,chown,file_inherit,directory_inherit" ~/Public

Note that this gives read & write access to all accounts in the staff group (which basically means all user accounts); if you want a bit more control, create a group in System Preferences > Users & Groups, and add just yourself and your friend's account to it, then use "group:yourgroupname" in the above command. Also, the inheritance only applies to items as they're created, so it won't apply to files and folders already in your Public folder; if you want it to apply to existing items, add chmod's -R option (chmod -R +a ...)