Files are shared in Mac OS X on your MacBook according to a set of rules called permissions, the ownership of the file (typically the person who saved the document the first time), and an access level shared by multiple users who are specified as a group. The combination of privileges, ownership, and group determines who can do what with the file.

When you (or the person with the administrator account on your MacBook) created your user account, you were automatically granted ownership of your Home folder and everything that it contains as well as any files or folders that you store in the Shared folder or another user’s Public folder.

Four possible actions are allowed through permissions:

  • Read Only: This action allows the user to open and read the file, which includes copying it to another location.

  • Read & Write: This permission grants full access to the file, including opening, reading, editing, saving, and deleting. Read & Write permission also allows the user to copy or move the file to another location.

  • Write Only (Drop Box): A neat permission setting that appears only with a folder — it allows access to copy an item to the folder, but not to see any files it contains. (Hence the informal name Drop Box, and the + [plus sign] icon added to the folder’s icon to identify it.)

    For example, a drop box is made to order for teachers: Students can submit homework by dragging their work to the teacher’s drop box.

  • No Access: This is just what it sounds like — the user can’t open the file, copy it, or move it.

No matter what permissions you’ve set, only the System Administrator (or root user) can copy items into another user’s Home folder using the Finder. Take my word for it on this one: Simply consider that this can’t be done, and stay as far away from the Root/System Administrator account as possible.

These permissions are set in the Info dialog for a file or folder (always accessible by pressing Command+I). If you’re setting the permissions for a folder, you can also elect to apply those same settings to all the enclosed items within the folder.