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Creating Basic Images with SIU

In this section you will learn how to create and modify basic network disk images. You can create network disk images using SIU from any Mac OS X v10.6 computer. All you need is a system with access to your source media and enough storage space to save the newly created image files. Similar to when you create cloned system images, the destination volume needs roughly two times the amount of available space as there is used space on the source volume.

Once you have created your network disk images, you can host them from a NetBoot server, as detailed in Chapter 5, “Deploying System Images.” It’s important to note that you don’t have to create the network disk image on the server where it will eventually be hosted. You can save the image to your Mac client’s system drive or an external drive, and then copy it to the appropriate location on your NetBoot server.

Create a Basic Network Disk Image

To create a basic NetBoot, NetInstall, or NetRestore image:

  1. Mount your source system volume.

    The source system can be either Mac OS X v10.6.x or Mac OS X Server v10.6.x. The source volume can be the original installation media, a nonbooted system volume, or a disk image containing either.

  2. Open /Applications/Server/System Image Utility.

    You will be presented with the basic NetBoot image-creation interface. System Image Utility automatically scans all mounted volumes for valid sources and lists them under Sources in the left column.

  3. Select the system volume you wish to make an image of from the Sources list.
  4. Select the appropriate button to define the type of image you want to create; NetBoot, NetInstall, or NetRestore.
  5. Click the Continue button once you have made your selections.
  6. Enter an image name and description.

    The image name will be displayed by any interface that allows you to select this image, including the Server Admin application and Startup Disk preferences.

  7. If you intend to host this network disk image on multiple servers, select the “Image will be served from more than one server” checkbox.

    Selecting this option will set the network image ID to a range that tells the NetBoot service to automatically provide load balancing if the image is shared from more than one source. If you’re not sure, simply leave the default setting, as this can be easily changed later.

  8. If you are creating a NetBoot or NetRestore image from installation media, you will need to configure a local administrator account.

    Enter a name, short name, and password (twice) to define the new local administrator account. You can also set the account picture by clicking the image at the right.

  9. When you are satisfied with your network disk image settings, click the Create button.
  10. Agree to the software license agreement to continue with the network disk image creation process.
  11. When prompted, enter a name and select a location to save the network disk image.

    The name you choose here is only used to set the name of the folder that contains the network disk image resources; it does not affect the image name you specified earlier.

    The save location can be any writable destination that has enough space to hold a copy of your network disk image. However, if you’re creating this image on the server that will be hosting it, you can save time by choosing the NetBoot share point. The default location for the NetBoot share point is the /Library/NetBoot/NetBootSP0/ folder.

  12. Click the Save button and then authenticate as an administrative user to initiate the network disk image creation process.

Creating a network disk image can take from a few minutes to a few hours, depending on the size of the image source, the type of image you’re creating, and the speed of your hardware configuration. SIU will show the progress of the creation process, and you can always click the Cancel button to stop it. For a more detailed log of the creation process, choose View > Show Log.

Modifying Network Disk Images

Modifying an existing network disk image is easy, as long as you don’t need to apply a major Mac OS X update to the system volume. System updates that change the Mac OS X version—for instance, from version 10.6.1 to 10.6.2—usually replace core system components such as the UNIX kernel. Because of the special system image format of a network disk image, a major Mac OS X update installation will not properly replace these items. If you need to update the version of Mac OS X in a network disk system volume, you will have to create a new image.

Network disk images are created by SIU as folders named with the .nbi extension. The system image file that Mac computers start up from when using the NetBoot service is inside the network disk .nbi folder. Inside a NetBoot image folder you will find “NetBoot.dmg,” while inside NetInstall and NetRestore images you will find “NetInstall.dmg.” Most modifications of network disk images are as simple as mounting this read/write system image volume, applying your changes, and then ejecting the volume. NetBoot system images usually have about a gigabyte of free space for making changes, but NetInstall and NetRestore images have very little room for making changes.

Modifying the Deployable System

Standard NetInstall images created from Mac OS X installation media can technically be modified, but making any useful change is difficult because the Mac OS X installation process is not easily editable.

However, you can easily access and replace the system image that is restored by a NetRestore image. Inside the NetRestore image folder you’ll find the “NetInstall.dmg” system image; mount this image by simply double-clicking on it. You’ll note the content of this disk image is the system used to start up Mac computers via the NetBoot service. This image content also includes the prepared system restore disk image located at /Volumes/NetInstall/System/Installation/Packages/System.dmg.

If you wish to use another deployment mechanism to restore this system image, simply copy the System.dmg out of the mounted NetInstall volume and deploy it as you wish. Conversely, you can replace this disk image with any other prepared (scanned for ASR) system image. Providing the system image file is named “System.dmg” and is in the correct folder, the NetRestore process will restore that system instead.

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