Create Bootable Copies of the OS X Mountain Lion Installer

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Create Bootable Copies of the OS X Mountain Lion Installer

Create Bootable Copies of the OS X Mountain Lion Installer
Tom Grill/Getty Images

OS X Mountain Lion is the second version of the Mac OS that Apple sells primarily through the Mac App Store. Apple's first adventure with direct digital download sales of its Mac operating system was OS X Lion, which actually went very well.

The one area where many Mac users have had a bit of a problem with downloading OSes from the Mac App Store is the lack of a physical installer, primarily a bootable DVD or USB flash drive. OS X Mountain Lion continues this trend by deleting the bootable installer as part of the Mountain Lion setup process.

You can always re-download the OS if you need to, or have the OS X Recovery HD that is created as part of the installation do a re-install for you, but for many of us, having the OS X installer on portable media (DVD or flash drive) is a must.

If you would like to create a bootable OS X Mountain Lion DVD or USB flash drive, this guide will walk you through the process.

What You Need

  • A dual-layer DVD. This type of DVD has two layers, which increases the available recording space to roughly 8.5 GB. The OS X Mountain Lion installer is just a smidgen too big to fit on a standard DVD. Dual-layer DVDs, also called DVD9, are available just about anywhere standard DVDs are sold.
    You can also use a USB flash drive that can hold 5 GB or more (8 GB and 16 GB are commonly available sizes) as your bootable media.
  • A valid copy of OS X Mountain Lion, which you must purchase and download from the Mac App Store. It will be stored in the Applications folder on your Mac; the file is called Install OS X Mountain Lion. Please note that you must create the bootable copy of the installer before you actually perform the Mountain Lion installation because the Mountain Lion setup process deletes the files you need to make the bootable installer copy.

If you have already installed Mountain Lion, but you want to create the bootable installer we describe here, you will need to re-download Mountain Lion from the Mac App Store.

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Locate the Mountain Lion Install Image

How to Copy The Mountain Lion Install Image
Screen shot courtesy of Coyote Moon, Inc.

The Mountain Lion install image that you need to create either the bootable DVD or the bootable USB flash drive is contained within the Install OS X Mountain Lion file we downloaded from the Mac App Store.

Because the image file is contained within the downloaded file, you need to copy it to the Desktop to make creating the bootable image as easy as possible.

  1. Open a Finder window, and navigate to your Applications folder (/Applications).
  2. Scroll through the list of files and locate the one named Install OS X Mountain Lion.
  3. Right-click the Install OS X Mountain Lion file and select Show Package Contents from the pop-up menu.
  4. You will see a folder named Contents in the Finder window.​
  5. Open the Contents folder, and then open the SharedSupport folder.
  6. You should see a file named InstallESD.dmg.
  7. Right-click the InstallESD.dmg file and select Copy InstallESD.dmg from the pop-up menu.
  8. Close the Finder window and return to the Desktop.
  9. Right-click on an empty area of the Desktop and select Paste Item from the pop-up menu.

Pasting the item to the Desktop can take a bit of time, so be patient.

When the process is finished, you'll have a copy of the InstallESD.dmg file that you need to create bootable copies.

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Burn a Bootable DVD of the OS X Mountain Lion Installer

Burn a Bootable DVD of OS X Mountain Lion
Screen shot courtesy of Coyote Moon, Inc.

With Mountain Lion's InstallESD.dmg file copied to the Desktop (see the previous page), you're ready to burn a bootable DVD of the installer. If you would rather create a bootable copy on a USB flash drive, you can skip these steps and move on to the next ones below.

  1. Insert a blank DVD into your Mac's optical drive.
  2. If a notice asks you what to do with the blank DVD, click the Ignore button. If your Mac is set up to automatically launch a DVD-related application when you insert a DVD, quit that application.
  3. Launch Disk Utility, located in /Applications/Utilities.
  4. Click the Burn icon, located in the top right corner of the Disk Utility window.
  5. Select the InstallESD.dmg file you copied to the Desktop in an earlier step.​
  6. Click the Burn button.
  7. Place a blank DVD into your Mac's optical drive and click the Burn button again.
  8. A bootable DVD containing OS X Mountain Lion will be created.
  9. When the burn process is complete, eject the DVD, add a label, and store the DVD in a safe location.
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Copy the OS X Mountain Lion Installer to a Bootable USB Flash Drive

Use Disk Utility to Partition the Flash Drive
Screen shot courtesy of Coyote Moon, Inc.

Creating a bootable copy of Mountain Lion on a USB flash drive isn't difficult; all you need is the InstallESD.dmg file that you previously copied to your Desktop (and a flash drive, of course).

Erase and Format the USB Flash Drive

  1. Insert the USB flash drive into your Mac's USB port.
  2. Launch Disk Utility, located in /Applications/Utilities.
  3. In the Disk Utility window that opens, scroll through the list of devices in the left-hand pane and select your USB flash device. It may be listed with multiple volume names. Do not select a volume name; instead, select the top-level name, which is usually the name of the device, such as 16GB SanDisk Ultra.
  4. Click the Partition tab.
  5. From the Partition Layout drop-down menu, select 1 Partition.
  6. Click the Options button.
  7. Make sure that GUID Partition Table is selected from the list of available partition schemes. Click OK. Warning: All data on the USB flash drive will be deleted.
  8. Click the Apply button.
  9. Disk Utility will ask you to confirm that you wish to partition the USB device. Click the Partition button.

The USB device will be erased and partitioned. When that process is complete, the flash drive is now ready for use as a bootable device for OS X Mountain Lion.

Copy the InstallESD.dmg File to the Flash Drive

  1. Make sure the USB flash device is selected in the device list in Disk Utility. Remember: do not select the volume name; select the device name.
  2. Click the Restore tab.
  3. Drag the InstallESD.dmg item from the device list (it will be near the bottom of Disk Utility's device list; you may need to scroll down to find it) to the Source field.
  4. Drag the USB flash device's volume name from the device list to the Destination field.
  5. Some versions of Disk Utility may include a box labeled Erase Destination; if yours does, make sure the box is checked.
  6. Click Restore.
  7. Disk Utility will ask if you really wish to perform a restore, which erases all information on the destination drive. Click Erase.
  8. If Disk Utility asks for your administrator password, provide the information and click OK.

Disk Utility will copy the InstallESD.dmg data to the USB flash device. When the copying is complete, you will have a bootable copy of OS X Mountain Lion ready for use.