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1. Cloned Image: Create Restore Image

When using the tools built into Mac OS X to create a deployable system disk image, you have a choice between two different methodologies: cloned system images and modular system images. With a cloned system image, you first set up a model computer that is configured with all the software and settings you intend to deploy. Create Image For Deployment Mac With Two. If you are using one Mac with two separate bootable volumes, one volume will be used to build. You should always use the new volume to build your model system image. When a user restarts the computer, the Setup.

Cloned Image: Create Restore Image

Once you have prepared and cleaned your model system volume, it’s finally time to create a restorable image from the model. The method covered in this section is essentially the “manual” method for creating a restorable image of a cloned system.

Create the Cloned Disk Image

Before you create the image, it’s a good idea to use Disk Utility’s Repair Disk feature on the model system volume. This will clean up potential volume structure issues that could have cropped up while you were building your system volume. If Disk Utility reports issues, you should run the Repair Disk process again until no issues are reported.

As you learned in Chapter 2, “Deploying Individual Items and Containers,” it’s fairly easy to create a disk image using the contents of a folder or volume. You can create disk images in the graphical interface using the Disk Image application and at the command line using the hdiutil command.

Here are a few tips to keep in mind when creating a cloned system disk image:

• It’s usually best to choose a new Disk Image from Folder and then select the model system volume as the source. This will always build an image with zero additional free space, so you can restore it to any drive that’s larger than the system image contents.
• Make sure to specify just the model system image volume, not the physical drive, as the source for the cloned system image.
• The cloned system image format must be read-only (optionally compressed) and not encrypted.
• If you choose to create a compressed image, make sure to have roughly twice the amount of free space available on the creation volume as the amount of used space on the model system volume.
• Using separate physical drives for the model system volume and the destination for the cloned system image will greatly speed up the disk image creation process.
• If you are unable to create the cloned system image because the system is reporting Resource Busy errors, unmount, but do not eject, the model system volume and then remount it again to create the cloned system image.

Preparing the Cloned System Image for Deployment

There is one last step to prepare your cloned system image for deployment. The cloned system image must be scanned in preparation for the Apple Software Restore (ASR) process. As you will learn in greater detail in Chapter 5, “Deploying System Images,” the ASR process is used to restore the system image contents to a storage volume for deployment. The image scanning process can be performed by the Disk Utility application or the asr command.

The image scan process calculates additional data checksums for the cloned system image and stores this information in the disk image file. This checksum data is later used to verify the system restoration process. The image scan process will also reorder the cloned system disk image file if it is not properly ordered for the network ASR process. If the disk image file needs to be reordered, the system will have to rewrite the file to the same volume. This reordering process is why you need roughly twice the free space on the creation system to prepare the cloned system image for deployment.

To scan your cloned system image from the Disk Utility application:

1. Open Disk Utility and choose Images > Scan Image for Restore.
2. In the Open dialog that appears, select your cloned system image.
3. Authenticate as an administrative user to initiate the scan process.

   Depending on the size of your system image and the speed of your hardware, it can take anywhere from a few minutes to a few hours to complete the image scan process. During this time Disk Utility will show a progress bar dialog. When the process is complete, this dialog will let you know whether the image scan process was successful.

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Scanning your cloned system image from the asr command is nearly as easy. The syntax is sudo asr imagescan -source followed by the path to the cloned system image. In the following example, Michelle scans the cloned system image she previously created, ClonedSystem.dmg, on the external Storage volume. The asr command also displays image scan progress and success messages.

Updating a Cloned System Image

One of the primary disadvantages of a cloned system image is that updates and changes are not easily made. Once a deployable system image is created, the image file itself can never be changed. Essentially, you have to replace your outdated cloned system image with a new cloned system image.

This process of having to build new cloned system images with every change is especially frustrating when you are testing and trying to work the kinks out of a new system deployment. Even the smallest change requires that you completely rebuild the entire system image.

There are three methods that you can use to update an existing cloned system image and still use your previous work as a starting point:

• Retain the original model system volume and apply your updates to the model system. Once the model system is updated, create a new cloned system image as outlined previously in this section.
• Restore the cloned system to a bootable volume as outlined in Chapter 5, “Deploying System Images.” Treat this restored volume as the new model system and apply your updates. Once your updates are complete, create a new cloned system image.
• Convert the cloned system image to a read/write disk image as outlined in Chapter 2, “Deploying Individual Items and Containers.” Mount the new read/write disk image that contains your cloned system and apply the changes to the mounted volume. Once your updates are complete, convert the system disk image back to a read-only format and then rescan the image for restore.

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Home > Articles > Apple > Operating Systems

1. Understanding System Image Creation

For many deployments, the best solution is a unified system disk image, which involves creating an ideal system, saving it to a disk image, and then deploying that system to all your computers. A unified system image requires a significant time investment up front, but it saves a great deal of time in the long run. Computers with identical configurations are much easier to manage; the fewer the differences between your deployed systems, the more uniform their performance and the less time spent diagnosing problems, updating software, and reconfiguring hardware.

A unified system image also greatly accelerates the deployment process for any deployment larger than a dozen computers. Once you have fully configured, tested, and created a custom system image on one computer, it can take as little as five minutes to copy it to another machine. Compare this with the time needed to deploy the system individually on every computer, and it’s easy to see the benefit of a deployable system disk image. In this chapter you will learn two general methods for creating deployable system disk images: cloning from a model system and building a modular system.

Understanding System Image Creation

Before starting the process of creating a system image, you must consider your deployment requirements: what software and configuration settings will be part of your system image? Consider your users, your systems, and the limitations of identical-system deployment on multiple computers. You also need to consider which of the two image creation methodologies will best suit your needs and abilities. The choices you make while planning your system image will affect every computer on which this system is deployed.

Defining System Image Requirements

When identifying all the specific items and configuration settings that you want to include in your system image, you must take into consideration the requirements of your users, the technical requirements of your systems, and the limitations of deploying an identical system on multiple computers.

User Requirements

Your primary focus when developing system image requirements should be on maximizing system usability, for both users and administrators. In some cases your target audience or usage policies may require tighter system control. This is often the case when users are inexperienced or cannot be trusted to manage any part of their systems. In this scenario you would limit application access and lock down as many system configuration settings as possible. You would also want to make things easy for the user by preconfiguring any system setting you can. In scenarios where you will be performing a significant amount of client management, you should incorporate directory services–based managed preferences.

In professional or creative environments, you may not need to be as restrictive in the application or settings, but you should still make sure to prepare the system based on the users’ needs; for instance, install third-party applications and peripheral drivers for inclusion with your system image.

No matter the level of your users, your system image should be as fully configured as possible, with both Apple and third-party software installed and updated, any necessary support files such as third-party drivers and fonts installed, and any systemwide configuration settings implemented. Note, though, that many settings are not well suited to deployment via a unified system image—more on this topic later in this section.

Computer-Specific System Requirements

Before you create your system image, you must determine which version of Mac OS X you intend to use. A major administrative advantage of using Mac OS X v10.6 and Mac OS X Server v10.6 is that they include all the hardware drivers necessary to work with any Mac that meets the minimum system requirements, allowing you to build a single system image that can work on any Mac.

Although creating a unified system image for computers that support Mac OS X v10.6 is simple, creating a system image for brand-new Macs can present a significant problem. In many cases, because the release of new Mac computers is not in sync with the release of the retail version of Mac OS X, a custom intermediate version of Mac OS X is created just to support the new hardware. However, new Macs cannot run versions of Mac OS X released prior to their introduction—that is, the oldest version of Mac OS X supported by a new Mac computer is the version that it ships with from the factory.

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Thus, a previously created system image will not work on new Mac computers, and you will have to create a new system image based on the version of Mac OS X that shipped with the new Macs. Further, these custom intermediate versions of Mac OS X may technically work with older Mac computers, but they are not officially supported by Apple to do so, presenting a problem when you are trying to build a single unified system image.

Fortunately, every general Mac OS X version update includes support for all Mac computers introduced prior to the update. For example, if you were to acquire new Macs that were introduced this week, the next general update of Mac OS X will include support for those new Macs and will support older hardware as well. Therefore, if you can wait to build your system image until you can base it on the next general update for Mac OS X, you can create a single system image for all your Macs. If you can’t wait that long, you will need to create a separate system image just for your new Macs.

It’s important to note that custom intermediate versions of Mac OS X for new computers do not use different version numbers from the general releases. They do, however, have different build numbers, which can be identified by clicking once on the version number from the About This Mac window.

Software Update Requirements

You should strive to build your system image using the latest versions of your selected software. To do this, you’ll need to collect and keep track of all the necessary software update installers that you’ll apply when building your system image.

First you need to determine and acquire the latest version updates for Apple software. Apple’s downloads website, www.apple.com/downloads/, lists all the latest updates and can be searched and browsed so you can locate and then download specific Apple software updates. However, it may not seem obvious which Apple updates are needed; for this reason you can open Software Update from the Apple menu.

Apple Software Update will compare your Mac’s current installed software with the latest versions available from Apple. Obviously, you should run this on one of your test deployment systems to verify exactly which updates are necessary. The Mac OS X v10.6 version of Software Update no longer allows you to download updates without installing them. Thus, if you want to acquire the updates for later installation or deployment, you will have to do so from Apple’s downloads website.

You should also verify that you are using the latest versions of third-party applications and drivers. Many third-party products feature a built-in automatic update system that will check online for updates. However, few of these third-party update systems will allow you to download the individual update installer so that you can later use it to build your system image. Again, in this case, visit the software developer’s website to download the individual update installers.

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Limitations of a Unified System Image

You should include as many configured settings as possible with your system image so you don’t have to spend time setting these items on each individual computer. However, there are many settings that you should not, or cannot, deploy with the same configuration to every computer.

For example, in most cases, user-specific settings should not be included with your system image. Computer-specific settings also should not be configured on the system image. For instance, a unique IP address and network name needs to be set for every Mac. Both user- and computer-specific settings are best handled using dedicated client management tools and techniques.

In deploying a Mac OS X Server system image, your primary goal will be to strike a balance between what you can safely configure as part of the generic server system image and what settings you must leave for after deployment.

Choosing a System Image Methodology

When using the tools built into Mac OS X to create a deployable system disk image, you have a choice between two different methodologies: cloned system images and modular system images.

With a cloned system image, you first set up a model computer that is configured with all the software and settings you intend to deploy. Then you create a duplicate copy of the system volume saved to a disk image that has been specially prepared for deployment.

The modular system image methodology, a newer method, requires a bit more work up front, but it has several advantages over the older method and is the Apple-recommended best practice. With this method you build a fresh system by installing a series of installation packages to a sparse disk image. The installations include the full Mac OS X system, any software updates, any additional Apple software, any third-party software, and any custom installation packages that you have created to set up your system image. This sparse image is then converted to a disk image that has been prepared for deployment.

Cloned System Image Pros and Cons

• Pro—Easier workflow for novice administrators

• Pro—Less time spent creating initial system images

• Con—Requires that the model computer be purged of any unnecessary or troublesome files

• Con—Prone to issues if model not properly “cleaned”

• Con—Prone to more issues when deploying to different models

• Con—Increased workload when creating multiple system images

• Con—Increased workload when it’s time to update system images

• Con—New system images are never consistent with prior images

• Con—Difficult to document and audit system image configurations

• Con—Increased workload to test system image modifications

Modular System Image Pros and Cons

• Pro—System images are clean because they have never been booted.

• Pro—System images have no model-specific settings.

• Pro—Apple updates won’t interfere with your customizations because they are always applied before your customizations.

• Pro—Your workload is lighter when creating multiple system images that require unique software and configurations.

• Pro—Your workload is decreased when it’s time to update system images.

• Pro—Multiple and updated system images are perfectly consistent for similar items every single time.

• Pro—All configurations are easily documented and easily audited.

• Pro—Testing of updates and image modifications are simpler.

• Pro—System image creation process is automated.

• Pro—It’s easy to integrate modular system images with system maintenance workflows and third-party deployment tools.

• Con—Workflow is more difficult for novice administrators.

• Con—You must create custom installation packages for some third-party items and any configuration settings.

• Con—You will spend more time creating an initial system image.

The cloned system image methodology requires less effort up front, and you can get your first image set up quickly. However, in the long run you’ll have to spend much more time fixing bugs, updating software, and adding modifications than with a modular system image. The modular system image methodology requires more initial effort to properly configure your first system image, but maintaining your systems will be much easier because you’ll be able to build new modular images with additional items and updated software.

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