Mac OS X for Unix Geeks

Disk Images

Many applications in Mac OS X do not require a special installer. Often, they can be installed by simply dragging the application’s folder or icon to a convenient location in the directory structure, usually the /Applications folder. Applications that are distributed this way are typically packaged as a disk image. A disk image is a file that, when double-clicked, creates a virtual volume that is mounted on the user’s desktop, as shown in Figure 6-7.

Figure 6-7. A disk image and its mounted volume

Inside Applications

Actually, an application is a folder with the extension .app , which is typically hidden from the user. This folder contains all of the application’s resources. To view the contents of an application bundle, Control-click on the application icon and select Show Package Contents from the pop-up menu. This will open the application’s Contents folder in the Finder.

Tip

You can turn a Java application into a .app with MRJAppBuilder (/Developer/Applications). Since Mac OS X comes with Java, you can place your Java application on a disk image, secure in the knowledge that any Mac OS X user can double-click on the application to launch it.

Disk images can be created either using Disk Copy (/Applications/Utilities) or via the command line (described later). There are two types of disk images. One is a dual fork disk image with an .img extension, and the other is a ...