How to Make a Mountain Lion Bootable USB Drive

If you're looking for a way to install Mac OS X Mountain Lion on multiple machines or want to have a backup installation media, creating a bootable USB drive is a great option. In this article, we'll walk you through the steps of making a Mountain Lion bootable USB drive.

To start, make sure your USB device has at least 8GB of free space. If it doesn't, you won't be able to create the bootable drive. Next, plug in your USB device and launch Disk Utility (/Applications/Utilities).

In Disk Utility, select your USB device from the list on the left and click the Erase tab across the top right. Make sure to highlight the flash drive itself (not the volume shown under it) before clicking the Erase button.

Once you've erased your USB device, close Disk Utility and follow these steps:

1. Download OSX Mountain Lion from the App Store. It will be downloaded to your Applications folder.

2. Right-click on 'Install Mac OS X Mountain Lion' installer and choose the option to 'Show Package Contents'.

3. Inside the Contents folder, you'll find a SharedSupport folder and inside that folder, you'll find the InstallESD.dmg. This is the 10.8 Mountain Lion boot disc image.

4. Copy InstallESD.dmg to another folder like your Desktop.

Now it's time to use Disk Utility to create the bootable USB drive. Launch Disk Utility again and select the USB device from the list on the left. Click the Partition button to continue.

Select the disk image InstallESD.dmg and click Open (or drag-and-drop the disk image into the Source area). In the Destination area, make sure that the USB device's name is showing.

Click on the newly created volume listed under the USB device on the left. A warning will pop-up asking if you're sure you want to partition the media. When you've finished, click the Apply button to format the USB device. Insure that Format is set to Mac OS X Extended (Journaled). You may now name the device in the Name textbox.

This will allow the Mac to boot from the drive. Select GUID Partition Table and click OK. Using the drop-down menu for Volume Scheme, choose 1 Partition as the partition scheme.

Highlight the partition by clicking on it in the space it is shown below the Volume Scheme drop-down and then click on Options underneath it. Confirm the dialog ensuring that you want to erase the device and all information on it.

Select the Partition tab on the top right. Then ensure that the Format drop-down menu is set to Mac OS Extended (Journaled) and click the Erase button.

That's it! You now have a bootable Mountain Lion USB drive that you can use to install Mac OS X 10.8 on multiple machines or as a backup installation media.

Make mountain lion bootable usb