Sharing Locally: The Public and Shared Folders

User Level:	any
Affects:	individual user
Terminal:	no

The simplest form of sharing in OS X is to make files available for other people who actually sit at your computer. Mac OS X has two ways of doing this.

What Does It Share?

Mac OS X has two special types of folders specifically designed to share files with other users of your computer. The first is a special folder called Shared, located in the main /Users directory. The Shared folder is different from other user folders in two significant ways. First, it does not correspond to any particular user; rather, it exists regardless of how many (or few) user accounts exist on your Mac. Second, all users can view the contents of the Shared directory, can move files to it, and can create files inside of it. In other words, as the name implies, it is a folder that is shared by all users.

The second way to share files with other local users is to use your personal Public folder, located at /Users/username/Public. Whereas most user-level folders prevent other users from even viewing their contents, the Public folder allows other users to view its contents and access files inside of it. You can make files available to other users by placing them in your own Public folder, and other users can share files with you by placing them in their own Public folder.

Tip 

The Public folder has a special folder inside of it called Drop Box. If you Get Info on this folder, you'll see that, for everyone but the owner, its permissions are set to "Write only (Drop Box)." Think of this folder as your own personal mailbox—other users can drop files inside, but no one except you can get them out, or even verify that they exist. This folder is OS X's way for users to exchange files securely.

There are two caveats I should mention when it comes to the Shared and Public directories. The first is that file permissions still apply. Documents created in these folders are set, by default, to allow other users Read Only access, and documents copied or moved to them retain their original permissions. In other words, if you want others to be able to edit a file that you place in one of these directories, you may need to manually change its permissions as discussed in Chapter 1. This includes the Drop Box—if you give someone a file you want them to be able to edit, be sure to give them Write access before putting it in their Drop Box.

The second caveat is that by default, placing files in the Public or Shared folders provides the same level of access to all other users. If you have a sensitive document to which you want to limit access to a single individual, a better approach is to use their Drop Box. However, what if you want to provide access to a file to a group of users, but not all users? The answer is to use groups, as discussed in Chapter 1. You can create a group that includes only those users to which you want to give access to a file. Using the Finder's Get Info command or a utility like XRay or FileXaminer, you would give the members of that group Read Only or Read & Write access, while restricting Others to No Access. You can then place the file in the Shared folder or your Public directory—even though the file will be in plain sight, only members of the group will be able to access it.

Finally, you may be wondering what the difference is between the Public and Shared folders. Besides the existence of the Drop Box in Public folders, there are two main differences. First, Public folders are set to allow Read & Write access to the owner, but Read Only access to other users, whereas the Shared folder allows Read & Write access for all users. Second, Public folders are accessible remotely via Personal File Sharing (which I'll talk about in a bit) by default, whereas the Shared folder is not.

Who Can Access Files?

Any user who has an account on your Mac has access to the main Shared folder and to every user's Public folder.

How Do I Configure It?

Other than being careful with the permissions of files you place in the Public or Shared directories, no configuration is necessary.

How Do Others Access Files?

Other users can access files in these folders by simply navigating to them in the Finder.

Sharing Files Locally Using Multiple Volumes/Drives

Although I cover the topic of multiple volumes and drives in more detail in Appendix B, I want to mention it here as it relates to sharing files and file security. If you have multiple hard drives or volumes (including multiple partitions of a single hard disk), you should be aware that the default permissions for files created on any non-boot volume are Read & Write for the owner, and Read Only for everyone else. Thus, saving a file to a non-boot volume is identical to saving it to a Public folder. This may be exactly what you want—many people use such a secondary volume as a place to share files. However, if it's not, you can change permissions for individual folders or documents on the volume (or for the entire volume) using the Finder's Get Info command. Another solution is to create files in a "private" area of your own user folder first, and then copy them to the non-boot volume (since files copied to a shared area retain their original permissions).

At the other extreme, perhaps you have an extra hard drive that you want to use for shared projects—what if you want all users to be able to read and write to all files? Simply select the drive on the Desktop or in a Finder window and select File ➣ Get Info. In the Ownership & Permissions panel, check the box next to "Ignore ownership on this volume." Now OS X will ignore any and all permissions and restrictions on files on that volume. (Note that this change requires admin access.)