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Creating an Emergency Startup Volume

Troubleshooters often find it useful to have a startup disk other than the one that's normally used—typically, the Mac's internal drive. Alternative startup disks can be convenient when you're doing something that cannot be done to the current startup drive (such as disk repairs with some utilities). They become especially valuable if the data on your default drive gets corrupted in such a way that your computer cannot start up from the disk. At these times, a bootable emergency disk becomes an essential tool for repairing the problem drive, or at least recovering data from it.

Because the Mac OS Install disc is bootable and provides access to Disk Utility, you can use it as an emergency boot disc. Third-party repair utilities also typically come on their own bootable CDs. Still, these discs may prove less useful as updated versions of the software are released, for which you do not have a CD. (In addition, as new models of Macs are released, it often takes time before an updated version of a third-party utility's CD, modified to start up the latest Macs, is released.) In any case, it's convenient to be able to create your own custom bootable emergency disk—one that contains all the software of your choosing.

In past years, emergency bootable volumes took the form of floppy disks or (more recently) CD-Rs or Zip disks. More recently, that emergency volume could have been a portable FireWire hard drive. In this section, I discuss how to set up an emergency volume using several different media. Of special interest are the procedures for making a custom bootable CD.

Creating a bootable volume in Mac OS 9 was about as simple as it could possibly be: You just dragged a copy of a System Folder to the volume, and (assuming the software was recent enough to run on the Mac in question) you were able to start up your Mac from that drive. This method worked with hard drives as well as most removable media (such as Zip disks). CDs, however, presented a special problem: A CD needed some special boot code for the Mac to recognize the disc as a startup volume at a point in the startup process when it typically would not yet have loaded the code needed to recognize CDs in the first place! This problem was solved by utilities such as Roxio's Toast, which created a bootable CD with the needed special code from any original that contained a System Folder. Even Mac OS X's Disk Utility can burn a bootable Mac OS 9 CD if you first create a disk image of a bootable CD for it to copy.

Creating a custom bootable Mac OS X volume presents considerably more difficulties. The primary reason is that the essential System files are not all in the Mac OS X System directory. In addition, numerous invisible files, mostly related to the underlying Unix OS, need to be copied as well. And there is the potential issue of setting up a default user account.

Thus, you cannot simply copy a Mac OS X System folder to a Zip disk, for example, and expect it to function as a startup volume. In fact, given that Zip discs max out at 250 MB, and a typical Mac OS X system can require more than 600 MB, it's unlikely that you'll be able to use a Zip disk as a Mac OS X startup disc under any circumstances.

Bootable hard drive

If you've divided your internal hard drive into several partitions, the simplest way to create an emergency startup volume would be to use a Mac OS X Install CD to install Mac OS X on more than one partition. You could then use the second Mac OS X installation as your emergency partition. One weakness of this approach is that if the entire hard drive fails, you will not be able to start up from any partition.

A better alternative is an external hard drive. Especially convenient when traveling are small, portable FireWire drives.

Bootable CD or DVD

For troubleshooters, by far the most useful and commonly used bootable disc is a bootable CD or DVD. So, if you own a CD or DVD burner (Apple's SuperDrive will make things go most smoothly), can you create one of these bootable discs yourself? Yes, with some limitations.

You can certainly create an exact copy of a bootable CD or DVD that will also be bootable, but making a useful customized bootable disc is not as simple.

Making a duplicate bootable CD/DVD

If all you want is to make an exact copy of a bootable disc (such as the Mac OS X Install disc) for use as an emergency disk, it's relatively easy to do.

However, don't expect to use the Finder's Burn Disc command (in the File menu) to accomplish this feat. At least as of Mac OS X 10.4, you could not create a copy of a bootable disc using this feature.

Toast, a commercial disc-burning application, can make a bootable Mac OS X disc—and using it is as simple as clicking the Copy tab, inserting the disc to be copied, and clicking the red Record button. This works especially well if you have two optical drives (only one needs to be RW)—one for the blank CD-R or DVD-R and another for the Mac OS X Install disc. If this doesn't work for some reason, first create a .dmg of the Install disc and then use Toast to copy the unmounted image file to the blank disc. You could do this by creating the image file via Disk Utility in Mac OS X. However, if you need to go this route, you might as well skip Toast altogether and just use Disk Utility.

To create a bootable copy of a Tiger Mac OS X Install DVD with Disk Utility:

  1. Booting from your hard drive, insert and mount the Mac OS X Install DVD.
  2. Launch Disk Utility.
  3. In the left-hand column, the Mac OS X Install DVD will be listed in the following manner: At the top of the hierarchy will be the name of the drive itself (for example, 2.6 GB PIONEER DVD-RW DVR-117D); the subheading under that name will be either Mac OS X Install DVD or Session 1; if the latter, the subheading under that name will be Mac OS X Install DVD.
  4. Select Mac OS X Install DVD (or, if Session 1 is listed, select it instead). Note: For multisession discs, each session would be listed separately. To create a multisession disc, check the "Leave disc appendable" box in Disk Utility's Burn Disc dialog (in Step 9, below). Otherwise, the instructions here assume you have a single-session disc.
  5. From the File > New submenu, choose "Disk image from {name of device}." The name of the device should be something like "disk1s3 (Mac OS X Install DVD)."
  6. In the Convert Image dialog, name the image. For Image Format, typically choose either "read-only" or "DVD/CD master" (which is what I recommend). Leave Encryption as "none." Note: The "read/write" format should be used if you intend to modify the contents of the image (which we are not doing here) before burning it. With this format, you can later mount the image and drag files to or from the mounted volume. Changes you make are saved to the image (.dmg) file. You then unmount the image before burning the image to a disc. Ideally, you should still choose DVD/CD master, read-only, or even compressed (if needed to conserve space) when setting up to burn the modified image.
  7. Click Save.
  8. Returning to the left-hand column of the Disk Utility window, select the image you just created. Click the Burn icon in the toolbar or select Burn from the Images menu.
  9. Insert a CD-R or DVD-R at the prompt in the Burn Disc dialog that appears. At this point, the Burn button in the dialog will become undimmed. Click it and wait for the burn to complete.

Making minor changes to the exact procedures and selections I have described here may still produce a successful bootable disc. I have not tried them all. But I have tried several different combinations, and this was the one that worked best for me. Feel free to experiment with other combinations if you don't share my success.

Note: In some cases, you may be able to download a .dmg file of a bootable disc from a Web site. Or you may create your own image with software other than Disk Utility. If so, you can drag the image file to the lower half of the left column of Disk Utility (where image files are listed). Once the image file appears in the list, you can go directly to Step 8 above.


Figure 3.24 Disk Utility's Burn Disc dialog in Tiger.

Making a modified copy of a bootable disc

The above procedure is all well and good. But what if you want to make a customized disc with your own utilities on it?

It may at first seem that the solution is to create a read/write image from the Mac OS X Install disc (as described in the previous section), and then add your own utilities to the image (deleting unneeded and nonessential files already on the image, if necessary). The problem is, a bootable disc created in this way does not load the Finder. In fact, the Finder is not even on the disc. Instead, the disc boots directly into the Installer utility, which is the only way the disc can start. Thus, although you may have other utilities on the drive, you would have no way to access them. Could you get the disc to boot into another utility instead of the Installer? It's possible to modify the rc.cdrom file (located in the /etc directory of a bootable CD) to get it to boot into another utility, but doing so is tricky enough that I wouldn't bother.

Apple has created software that developers can use to create custom bootable CDs. It is this software that the developers of programs such as Alsoft's DiskWarrior ( and Micromat's TechTool Pro ( use to create the bootable discs. However, Apple has not made this development tool available to the public. In fact, Apple even limits its availability to "qualified" developers who can demonstrate a need for making such discs. Clearly, Apple does not want to encourage the creation of custom bootable discs. And even in these cases, the discs typically do not include a Finder and thus cannot access the Desktop.

So what can you do here? Get the shareware utility BootCD (which can also be used to make a bootable DVD).

Making a custom bootable CD with Boot CD

BootCD ( allows you to create a bootable CD that contains a Finder and a Dock. The Dock can be set up to contain any applications you choose. Here is an overview of how to use it.

  1. Launch BootCD. Type in the desired name in the Volume Name field. Note: If you are going to make a bootable DVD, change the Disk Size here from the default of 650 MB to the size of the DVD (typically, 2600 MB). Otherwise, leave this value alone. Although this should work to make the disc bootable, it will still install only the same limited system software that it would install on a CD. If you want to change the RAM Disk Size, you can also do so; however, there should rarely be a need to so this, so I don't recommend it.
  2. Click the Create Bootable CD Image button.
  3. Give a name to the .dmg file that BootCD will create; then click Save.
  4. Choose which applications you would like to include on the CD and put in the Dock that is used when you boot from the CD. You do this via a file-browser window that appears. Typically, you would add utilities that you might need for repair or recovery in an emergency. Click Open to add a utility. Click Cancel when finished. Disk Utility, Console, and Terminal are automatically included, so you don't need to select them.
  5. Quit BootCD, launch Disk Utility, and burn a CD of the disk image you created.

To use your newly created bootable CD, insert it into your CD/DVD drive and then restart. Boot from the CD (by holding down the C key at startup). When startup is complete, you should be at the Finder. There will be a Dock that contains all the utilities you selected (plus Disk Utility, Console, and Terminal). Your startup-drive volume/partitions will also be mounted. You have root user status at this point. (BootCD has the root password set to BootCD.)

With the full contents of the hard drive now accessible, you can work with most applications on the drive (in addition to the emergency utilities on the CD). I could run the Chess game or create a document in TextEdit, for example. However, since the CD is read-only, you won't be able to save documents to the CD or to save preferences to applications.

The Restart, Shut Down, and Log Out commands in the Apple menu do not work on a CD created with BootCD. To reboot again from your hard drive, use the reboot command in Terminal. To make sure you don't reboot from the CD, hold down the Eject button on your keyboard until the CD ejects.

Note: The steps in this section are accurate for the Panther version of BootCD. This version is not compatible with Tiger! A Tiger version of BootCD was still in development as of this writing. The new version may, of course, work a bit differently than described here, so be sure to read the documentation.

See "Creating a Mac OS X Bootable CD" ( for more technical information on creating a bootable CD.


Figure 3.25 Making a bootable disc with BootCD.

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