Recently, several intrepid Mac administrators have demonstrated ways to create a "universally" bootable install of Mac OS X 10.4.5 - a boot disk/image that boots both PowerPC-based and Intel-based Macintoshes. This development could simplify an administrator's life, or usher in a new set of challenges.
Universal OS X install creation
Andrew Mortenson was the first to post his method for creating a universal OS X install using radmind.
Sam Agnew extended this technique to create a Universal NetBoot image.
Rolf Kocherhans posted another technique here.
Apple does not support such a beast, but has indicated that a "Universal" OS is a future goal.
Why Universal?
A Universal image is appealing for several reasons. An admin need carry only a single FireWire drive with a single partition, containing the Universal boot image and any diagnostic and repair utilities. A single, universal NetBoot image could be created. In theory, a universal image would decrease the work an admin would need to do - instead of maintaining two images (one for PowerPC and one for Intel), our admin could focus his/her efforts on a single image.
Issues
But there are several potential issues to consider before using a home-grown universal image for anything beyond testing and administrative tasks.
The first issue to consider is stability: since Apple does not support this configuration, and has not tested this configuration, you may experience issues with kernel extensions or hardware drivers. For example, USB drivers from the Intel build have not been tested against PowerPC USB hardware. There may be bugs that cause data loss lurking in a home-grown Universal build.
A more important consideration is ongoing supportability of a home-grown universal image. It's difficult to apply updates and patches from Apple to such an image. If you run a home-grown universal image on an Intel Mac, Software Update will show and allow you to install all applicable Intel updates. But the same image on a PowerPC Mac confuses Software Update, presumably because it sees a build number that it thinks is for Intel running on PowerPC hardware. Therefore, Software Update refuses to display any OS updates or patches at all.
It would not be safe to assume that applying the Intel version of a given update to your universal build is sufficient - there's no guarentee that the Intel version is a superset of the PowerPC version. Therefore, to update a home-grown universal image, you'd really need to maintain seperate PowerPC and Intel builds, update them seperately, and then use the same mechanism to combine them into a single build that you used to create your original universal build. (And then repeat all the testing you should have done when you did your original universal build.)
The need to do this eliminates a lot of the attractiveness of a universal build: you still need to maintain seperate PowerPC and Intel builds. In fact, it actually adds more work, since you pick up the additional task of recombining the two architectures. Finally, you now have an unsupported version of the OS, so if you encounter any problems, you'll need to revert to the processor-specific version of OS to troubleshoot.
These considerations may not be as important for a diagnostic drive or NetBoot image. These may not need to be updated or patched very frequently, and if there are problems with some parts of the OS, these problems may not be important as long as the machine boots and utilites you wish to use run.
Conclusions
Given these issues, a prudent administrator would not rush to deploy a universal 10.4.5 on production machines. A universal image is a helpful and convienent addition to an administrator's set of tools, but comes with a set of risks and challenges. Consider these challenges carefully before deploying this solution. |
