In our discussion about the filesystem, you’ve no doubt identified a certain amount of redundancy. There’s a Library folder at the root of the filesystem, one in your Home folder, and one in the System folder. And if you create an Applications folder in your Home folder to store applications that aren’t for use by others, you’ll note that it automatically gets the same folder icon as the Applications folder at the root of the filesystem, as shown in Figure 3-5.
This is the result of a concept known as filesystem domains and is structured to allow multiple users to share the same system or to be hosted on a server so they can use multiple systems and yet provide a consistent experience.
There are four domains in Mac OS X:
- User
Contains the resources for a user logged into the system. As you would expect from the similarity of descriptions, this domain is contained within the user’s Home folder.
- Local
Contains the resources that users of a particular system share with each other. The Local domain consists of the Applications and Library folders at the root of the filesystem. These resources are available to users of the system but are not available to users on networked computers.
- Network
Contains the resources available to all users of a local area network. Applications, documents, and other resources located in this domain are available on any machine that is part of the network. The folders that hold this domain vary according to network setup but typically appear as a Network folder in the Finder.
- System
Contains the resources required for the system to run. These resources are part of the operating system installation and can be modified only by administrative users.
When a resource is requested by an application, Mac OS X searches these domains—in the order above—to satisfy the request. For example, when an application requests a particular font, the system will search the Fonts directory in the User domain first. If the system doesn’t find the font there, it will look in the Local domain. If it doesn’t find it there, it will look in the Network domain , and finally it will look in the System domain .
This hierarchical search allows a user’s configuration file to override a system-wide preference. Furthermore, the consistency in naming of directories between the domains, such as the Library directory that appears in each domain, allows for easy management of resources.