How to create an OS X multiboot USB install drive

In an ideal world, sysadmins everywhere would only need to manage one or two operating systems–one desktop, one server–and nothing else. Unfortunately, business operations often dictate a different method than that, leaving it up to IT to bridge the gaps caused by fragmentation between multiple OS, hardware, and software instances.

For IT staffers, there’s seemingly no end to the number of tools they must carry with them, doubly so if they provide mobile support. Below is a solution to ease the load by providing access to any versions of OS X in one small, easy-to-carry, bootable flash drive.

There are a few requirements I’d like to share with you prior to beginning the tutorial:

• Apple computer with OS X 10.9+
• Install DVD media/DMG or installer for each version of OS X to be included
• USB flash drive with at least 8 GB for each version of OS X to be supported

When considering the requirements, particularly the flash drive size and speed, I recommend accommodating a minimum of 8 GB per OS X installer and preferably supporting USB 3.0 specification for faster file transfers as opposed to USB 2.0, which will work admirably, but slower. Also, since many Macs include SD card readers, a large capacity SD card could be used instead of a USB drive as well.

I. Partitioning the drive

For the purposes of this article, I’ll be creating three installers of OS X: 10.8, 10.9, and 10.10. However, the limit is really based on the total capacity of the drive to be used.

1. Launch Disk Utility.app and partition the external drive as three separate partitions of 8 GB each. I suggest naming each partition with the OS X version that will occupy the space to make it easier to identify later (Figure A).
   Figure A
   
2. Click the Options button, select the GUID Partition Table, and then click OK and Apply to commit the changes (Figure B).
   Figure B
   

With the drive now partitioned properly, see the sections below to go about copying the media/installer contents to the drive. Certain versions of OS X will require a different procedure to complete.

II. Apple OS X 10.7 (Lion), 10.8 (Mountain Lion)

1. Right-click the installer and select Show Package Contents from the context menu (Figure C). This reveals the contents of the installer itself and makes navigating the structure possible.
   Figure C
   
2. Drill-down through the Contents | Shared Support directories and drag-drop the InstallESD.dmg to the desktop (Figure D).
   Figure D
   
3. Launch Disk Utility and click on the partition to copy the install files to, then click the Restore tab. Next, click the Image button next to Source and point to the InstallESD.dmg file recently copied to the desktop. Next, drag-and-drop the partition created on the USB to the text box next to Destination (Figure E).
   Figure E
   
4. Once the source and destination fields are selected, click the Restore button. You’ll be prompted to confirm that the process will erase the contents of the partition by clicking Erase (Figure F).
   Figure F
   
5. The process takes about 30 minutes, depending on the speed of the computer. However, once it’s completed, the partition will be ready to be used to install OS X. Simply repeat the steps in this section to create an installer for 10.7 and 10.8 (Figure G).
   Figure G
   

III. Apple OS X 10.4 (Tiger), 10.5 (Leopard), 10.6 (Snow Leopard)

Since OS X (10.4, 10.5 and 10.6) were released as bootable DVDs, the process for these is slightly different and significantly slower, because the optical drives read data at a far slower rate than mechanical hard drives and solid-state drives. For this process, either the original DVD media or ISO/DMG images of the DVD are required.

1. Launch Disk Utility and click on the partition to copy the install files to, then click the Restore tab. Next, click the Image button next to Source and point to the DVD drive or ISO/DMG. Drag-drop the partition created on the USB to the text box next to Destination (Figure H).
   Figure H
   
2. Once the source and destination fields are selected, click the Restore button. You’ll be prompted to confirm that the process will erase the contents of the partition by clicking Erase.
3. The process takes about 30 minutes, depending on the speed of the computer. However once it’s completed, the partition will be ready to be used to install OS X. Simply repeat the steps in this section to create an installer for 10.4, 10.5, and 10.6, as needed.

IV. Apple OS X 10.9 (Mavericks) and 10.10 (Yosemite)

1. Launch Terminal.app and enter the following command:
   sudo /Applications/Install\ OS\ X\ Yosemite.app/Contents/Resources/createinstallmedia –volume /Volumes/DRIVE_LABEL –applicationpath /Applications/Install\ OS\ X\ Yosemite.app –nointeraction
   By default, OS X stores the installers downloaded from the Mac App Store in the Applications directory. If your installers are stored elsewhere, modify the path accordingly. Also, “DRIVE_LABEL” should be changed to reflect the name of the USB partition that you’ll be copying the installer files to. If you named it by the version number (10.x) as recommended above, you’ll use that for the volume name (Figure I).
   Figure I
   
2. When prompted to authenticate, enter your admin-level password (Figure J).
   Figure J
   
3. The process will first erase the partition and then transfer the installer files over (Figure K).
   Figure K
   
4. Second, the process will make the drive bootable and copy the boot files over (Figure L).
   Figure L
   
5. Depending on the computer’s specifications, the process takes approximately 20 minutes to complete. However, once it’s done, the partition will be ready to install OS X. Simply repeat the steps in this section to create an installer for 10.9 and 10.10, as necessary (Figure M).
   Figure M
   

As you can see in Figure N, I carry all versions of OS X–from 10.5-10.11–since I’ve found that most every client has a different support need than the next, and I like to be prepared for that.
Figure N