Create a Bootable USB Flash Drive for OS X 10.9 Mavericks in 5 Steps

If you have multiple Apple computers to upgrade to OS X Mavericks, the best option is to download it from the App Store once, create a bootable USB flash drive, and then install the rest without downloading each time. So how do you do this?

First, keep in mind that this bootable image will only work on current Macs and older. New Macs will require an updated installer. So you’d have to download the Mavericks installer from the App Store again, and follow these instructions to create an updated boot drive.

In order to create a bootable flash drive, you will need:

  1. Minimum 8GB USB drive formatted with Mac OS X Extended, Journaled partition.
  2. Install OS X Mavericks.app downloaded from the Mac App Store.

Step One: Format the Destination
Use Disk Utility to format your USB flash drive as a Mac OS Extended (Journaled) using a GUID partition table.

Step Two: The Installer Image
Find the file named InstallESD.dmg within the Mavericks installer app by right-clicking (or Control+click) and choose Show Package Contents. Double click and mount this disk image.

Step Three: Mount the Base System Image
You need to mount another file within InstallESD.dmg, and this file is named *BaseSystem.dmg”. Since this file is invisible, you have to mount it using Terminal so that Disk Utility can see it. Open the Terminal app (in /Application/Utilities), and then type the following:

open /Volumes/OS X Install ESD/BaseSystem.dmg

Step Four: Restore the Bootable Base System
Make sure your USB flash drive is mounted, and in Disk Utility, select BaseSystem.dmg (not OS X Base System) in Disk Utility’s sidebar, and then click the Restore tab in the right pane. Drag the USB flash drive name into the Destination box in the right pane. Then click the Restore button and a bootable OS X Mavericks base system will be created. If prompted, enter an Administrator user name and password.

When it’s complete, in Disk Utility, select BaseSystem.dmg on the left (not OS X Base System) and click the Eject button in the toolbar. This unmounts the disk image named OS X Base System. If you don’t do this, you’ll have two mounted volumes named OS X Base System, which makes the next step more confusing. I also like to rename the flash drive at this point.

Step Five: Add the Mavericks Installer Packages
Open the destination USB flash drive and navigate to the System folder, and then open the Installation folder. You’ll see an alias named Packages. Delete that alias. Open the mounted OS X Install ESD volume, and you’ll see a folder named Packages. Drag that folder into the Installation folder on your destination drive (where the alias was). The folder is about 5GB in size, so the copy will take a while, especially if you’re copying to a slow flash drive.