Create Bootable Copies of the OS X Mountain Lion Installer

Make a bootable Mountain Lion installer from a DVD or flash drive

Because OS X Mountain Lion is a software download, it doesn't include a physical installer in the form of a bootable DVD or USB flash drive. For some Mac users, having the OS X installer on portable media, such as a DVD or flash drive, is helpful when making a clean install on a startup drive.

This guide walks you through the process of creating a bootable OS X Mountain Lion installer DVD or USB flash drive.

Apple ended support for OS X Mountain Lion in August 2016, but it remains available for purchase at the Apple Store. Make a bootable flash installer of OS X or macOS if you have a more recent version.

What You Need

You need either a dual-layer DVD and a burner or a USB flash drive. The dual-layer DVD has two layers, which increases the available recording space to about 8.5 GB. The OS X Mountain Lion installer is a bit too large to fit on a standard DVD. Dual-layer DVDs are available anywhere standard DVDs are sold. If your Mac doesn't have a built-in SuperDrive, use an external DVD burner.

Alternatively, use a USB flash drive that can hold at least 5 GB as your bootable media. 8 GB and 16 GB flash drives are also commonly available.

Download a copy of OS X Mountain Lion, which you must purchase at the online Apple Store and download it from the Mac App Store. It is stored in the Applications folder on a Mac. The file is called Install OS X Mountain Lion.

Create the bootable copy of the installer before you perform the Mountain Lion installation. The setup process deletes the files you need to make the bootable installer copy.

Locate the Mountain Lion Install Image

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

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

  1. Open a Finder window and go to the Applications folder (/User/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.

  4. Open the Contents folder, then open the SharedSupport folder. You should see a file named InstallESD.dmg.

  5. Right-click the InstallESD.dmg file, then select Copy InstallESD.dmg.

    How to Copy The Mountain Lion Install Image
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  6. Close the Finder window and return to the Desktop.

  7. Right-click an empty area of the Desktop, then select Paste Item.

Pasting the item to the Desktop takes time. When the process finishes, you have a copy of the InstallESD.dmg file that you need to create bootable copies sitting on the Desktop.

Burn a Bootable DVD of the OS X Mountain Lion Installer

With Mountain Lion's InstallESD.dmg file copied to the Desktop, you're ready to burn a bootable DVD of the installer.

  1. Insert a blank DVD into the Mac's optical drive.

  2. If a notice asks you what to do with the blank DVD, select Ignore. If the Mac is set up to automatically launch a DVD-related application when you insert a DVD, quit that application.

  3. Launch Disk Utility, which is located in User/Applications/Utilities.

  4. Select Burn, located in the upper-right corner of the Disk Utility window.

  5. Select the InstallESD.dmg file you copied to the Desktop.​

  6. Select Burn.

  7. Place a blank DVD into the Mac's optical drive, then select Burn to create a bootable DVD containing OS X Mountain Lion.

  8. When the burn process is complete, eject the DVD, add a label, and store the DVD in a safe location.

Copy OS X Mountain Lion Installer to a Bootable USB Flash Drive

If you can't burn DVDs, use a bootable USB flash drive. Creating a bootable copy of Mountain Lion on a flash drive isn't difficult. All you need is the InstallESD.dmg file that you copied to the Desktop and the flash drive.

Before you begin, erase and format the USB flash drive. Here's how:

  1. Insert the USB flash drive into the Mac's USB port.

  2. Launch Disk Utility, which is located in /Applications/Utilities.

  3. In the Disk Utility window, scroll through the list of devices in the left panel and select the 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 16 GB SanDisk Ultra.

  4. Select the Partition tab.

  5. From the Partition Layout drop-down menu, select 1 Partition.

  6. Select Options.

  7. Select GUID Partition Table in the list of available partition schemes, then select OK. All data on the USB flash drive will be deleted.

  8. Select Apply.

  9. Disk Utility asks you to confirm that you want to partition the USB device. Select Partition.

The USB device is erased and partitioned. When that process is complete, the flash drive is ready for you to copy the InstallESD.dmg file to the drive. Here's how:

  1. In Disk Utility, select the USB flash device in the device list. Do not select the volume name; select the device name.

  2. Select the Restore tab.

  3. Drag the InstallESD.dmg item from the device list to the Source field. It is near the bottom of the Disk Utility device list. You may need to scroll down to find it.

  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 an Erase Destination check box. If yours does, select the check box.

  6. Select Restore.

  7. Disk Utility asks you to confirm that you want to perform a restore, which erases all information on the destination drive. Select Erase.

  8. If Disk Utility asks for your administrator password, provide the information and select OK.

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