Betalogue

In all my years of providing Mac troubleshooting services to Mac OS X users, I have never once had to use an external hard drive as a bootable device. I have certainly thought, on occasion, that it might have been convenient to have such a thing, but usually I am able to do all my work as long as I have the original system disks that came with the machine, and my DiskWarrior CD (a bootable disk) for hard disk problems. (Occasionally, I also have to boot a machine in Target Disk mode and access it from another machine. But it’s fairly rare.)

Then in the past couple of weeks I have had two different requests for help with the installation of Mac OS X 10.4 on computers without a DVD drive. This was an interesting challenge and I figured I should explore the issue further, knowing that Mac OS X is designed for network installations, etc. I suspected that this should be possible, even if not fully supported by Apple. But of course I would definitely need to be able to use an external drive as a bootable device and somehow run the installation from there.

By default, Mac OS X 10.4 comes on a single DVD, and most people I provide tech support services to are unaware of the exact nature of the built-in drive in their machine. It’s only when they try to load a DVD such as the Mac OS X 10.4 install disk that they realize that it’s not working and they need me to explain to them that their machine is rather old and only has a CD drive, which cannot read DVDs.

Now, when Mac OS X 10.4 first came out, Apple did provide an option to obtain a set of system installation CDs in replacement for the DVD installation disk. It is still mentioned on this page. But if you follow the link to the “Mac OS X Upgrade” web site, it actually redirects you to the main Mac OS X page.

The option might still be available somewhere, but Apple is obviously not putting much effort into making it available to their customers. In Apple’s view, Mac OS X 10.4 is now an old system for old machines, and we all know that Apple has more than a tendency to ignore the needs of people with older machines. (As far as I can tell, you cannot even purchase Mac OS X 10.4 from the Apple Store any longer.)

So, what to do? The two people asking for my help were the respective owners of an older eMac and an old Power Mac G4 (450 MHz). They both have FireWire connections, but I don’t have an external DVD drive, and I don’t know anyone who has one.

Based on my research online, in such a situation there are two options. One is to boot from the system disk on a machine that has an internal DVD drive (such as a laptop) and then boot the target machine in Target Disk mode and plug it into the other machine as an external drive, using the external drive as the destination volume for the system installation.

I didn’t try that, in part because my wife’s laptop was otherwise engaged at the time, and in part because this approach assumes that you always have a portable machine that can boot in Mac OS X 10.4 readily available. I was looking for a more convenient option.

The other option that I found during my research is to use an iPod as the system installation disk. I found this tip, which summarily described the procedure required to turn the iPod into such a system installation disk. The tip did not provide all the required information and I had to make several attempts before succeeding, so I thought I would share the additional information here.

First of all, I should note that I only tried this with a four-year-old FireWire iPod. iPods made in the past three or three-and-a-half years no longer work with a FireWire connection (they all use USB), and I don’t know if they can be turned into bootable volumes. In any case, the machines I am talking about here (the G4 and the eMac) are older machines without USB 2.0 connections, so a USB connection would be out of the question anyway. The iPod I used is my wife’s old iPod mini, which is still working fine after all these years. I imagine that if I had not used a FireWire iPod, I would have had to use an external FireWire drive.

The first problem I encountered was when trying to erase the iPod’s hard drive in Disk Utility. The operation failed and left the iPod in an unusable state. It would no longer mount or show up in Disk Utility. I suspect the failure might have had to do with the fact that iTunes was up and running at the time. It seems to me that, when an iPod is connected to your machine and iTunes is running, there can sometimes be problems with using the iPod as an external drive in the Finder or in Disk Utility.

In any case, I ended up using iTunes to restore the iPod to its factory defaults, and then I quit iTunes altogether. The iPod was still mounted as an external drive. I didn’t try to erase the iPod again. I simply moved on to the next step, which was to create a disk image of the Mac OS X 10.4 install disk which I could use to turn the iPod into a bootable Mac OS X 10.4 install volume.

What the tip mentioned above does not tell you is that there are only certain types of disk images that work for this purpose. I had to try several times until I found, via the man page for the asr command, that you need to create a disk image of the type “read-only” or “compressed”:

Use Disk Utility’s “Images -> New -> Image from Folder…” function and select the root of the
volume. Save the image as read-only or compressed. “Images->New->Image from ” is not
recommended on 10.3.x.

Admittedly, “compressed” was the default option when I first tried to create my disk image, but I didn’t trust Disk Utility (and didn’t see the point of creating a compressed image for what was essentially just a temporarily used disk image stored somewhere on one of my hard drives), so I changed it to “read/write.” The disk image creation process was fast enough, but when I then tried the next step (the “Restore” operation below), it didn’t work.

The “CD/DVD master” option (which creates a “.cdr” disk image) is even worse, as it creates a type of disk image that is not even recognized for the “Restore” operation.

Finally I created a “read-only” disk image, and that worked. I suspect, based on what the man page for asr says, that “compressed” would have worked as well. I should also note that I didn’t use the “Disk Image from Folder…” function as indicated by the man page for asr, but the “Disk Image from XXX…,” where “XXX” is the name of the Mac OS X 10.4 install DVD volume. It does not seem to make any difference in Mac OS X 10.5 whether you create the image from the DVD as a “device” or as a “folder,” at least for the purpose of creating a bootable system volume.

The next step is to use this disk image to turn the iPod into a bootable Mac OS X 10.4 install volume. For this, you need to use the “Restore” tab in Disk Utility. As far as I can tell, in spite of what the Disk Utility interface implies, this particular tab has nothing to do with which volume is currently selected in the list of volumes on the left-hand side. In the “Restore” tab, you simple select the disk image that you’ve just created as the source, and then drag and drop the iPod as a volume onto the “Destination” field.

Before you can proceed, however, you still have one more thing to do, which is to run the “Scan Image for Restore…” command in Disk Utility’s “Image” menu. This command performs checks that are described in detail in the man page for asr. They are required.

Once that is done, you should be able to click on the “Restore” button in Disk Utility’s “Restore” tab. You can also check the “Erase destination” option in order to get Disk Utility to erase the iPod’s contents before “restoring” the system.

The “restoring” process takes a little while, but once it is done, the contents of the iPod are indeed the same as the contents of the Mac OS X 10.4 install DVD. The iPod itself is even called “Mac OS X Install DVD.” And the iPod is ready to function as a bootable Mac OS X 10.4 install volume.

I was able to use it to install Mac OS X 10.4 on my client’s old Power Mac G4 (450 MHz) yesterday. It went without a hitch. It’s not particularly faster than installing from the DVD, but it works just as well, and of course it works with a machine that has no DVD drive. I see no reason why it won’t work on the eMac as well.

As far as I can tell, the iPod is still usable as an iPod, i.e. you can add music, notes, etc. to it without interfering with the ability of the iPod to function as a bootable Mac OS X 10.4 install volume. Both functions can coexist on the iPod, as long as you have enough room. (The Mac OS X 10.4 install takes up 2.75 GB of disk space, which leaves a little over 1 GB free on this particular iPod mini.)

I imagine you can also copy other applications into the iPod’s “Applications” folder, although I am not sure how you would access them from within the Mac OS X installer application, which is automatically launched when you boot from the iPod. (I’ll have to experiment with that later on.)

This entry was posted by Pierre Igot on Tuesday, August 26th, 2008 at 10:08 am and is filed under Macintosh. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.