Create a Bootable Flash Drive with OS X Lion Installer

OS X Lion and its downloadable installer create a conundrum for Mac users who would like to have bootable media from which to install Lion.

The reason many people want to have a bootable Lion installer is to create clean installs, that is, install Lion on a freshly formatted hard drive that doesn't contain any previous OS. The other major reason to want a bootable Lion installer is for emergency booting and repair of your Mac's hard drive.

It's true that Lion creates a bootable Recovery Partition that you can use for troubleshooting. But the Recovery Partition is only usable if your drive is in basic working order. If your drive has a corrupt partition table, or you've replaced the hard drive, then the Recovery Partition is downright useless.

Since we have valid reasons for wanting a bootable copy of the Lion installer, we're going to show you how to create one using a USB flash drive. If you would rather create a bootable DVD of the Lion installer, we've got you covered there, too. Take a look at:

Create a Bootable DVD Copy of OS X Lion Installer

If you're ready to create a bootable USB flash version of Lion, then let's continue.

What you need:

• OS X Lion installer. This is available from the Mac App Store.
• 8 GB USB flash drive. You can use a larger drive if you wish, but more important than the size of the flash drive is its speed. If you're buying a new flash drive just for Lion, I recommend buying one of the fastest available. While slow (read: inexpensive) flash drives will work fine, you'll find that both the time it takes to create the bootable flash copy of the OS X Lion installer, and the time it takes to install Lion on a target drive, will be somewhat long.

• Some free time. The creation time varies by the speed of the USB flash drive, but plan on 30 minutes to over an hour.

Let's get started.

The flash drive you're using to create a bootable Lion installer must be erased and formatted to use the GUID Partition Table and the Mac OS X Extended (Journaled) file system.

Erase and Format Your Flash Drive

If this is a new USB flash drive, you may discover that it has been pre-formatted for use with Windows. If you've already been using the flash drive with your Mac, it may already be formatted correctly, but it's still best to erase and format the flash drive to ensure that the OS X Lion installer you copy to the flash drive will boot properly.

1. Insert the USB flash drive into your Mac's USB port.
2. Launch Disk Utility, located at /Applications/Utilities.
3. In the Disk Utility window, look for the flash drive in the list of attached devices. Look for the device name, which usually appears as the drive size followed by the manufacturer's name, such as 16 GB SanDisk Cruzer. Select the drive (not the volume name, which may appear below the drive manufacturer's name), and click the Partition tab.
4. Use the Volume Scheme drop-down window to select 1 Partition.
5. Enter a name for the volume you're about to create. I prefer to use the name that Apple originally assigned to the Lion installer image that we'll copy in a later step, so I enter Mac OS X Install ESD as the volume's name.
6. Make sure the Format drop-down menu is set to Mac OS X Extended (Journaled).
7. Click the Options button, select GUID as the Partition Table type, and click OK.

8. Warning: All data on the USB flash drive will be erased

9. Click the Apply button.
10. Disk Utility will display a sheet asking if you're sure you want to partition your USB flash drive. Click Partition to continue.

1. Once Disk Utility finishes formatting and partitioning the USB flash drive, quit Disk Utility.

With the USB flash drive prepared, it's time to move on to preparing and copying the OS X Lion installer image.

The OS X Lion installer application that you downloaded from the Mac App Store includes an embedded bootable image that the application uses during the install process. In order to create our own USB flash-drive-based bootable Lion installer, we simply need to copy this embedded image to the flash drive.

We're going to use Disk Utility to clone the OS X Lion installer image to the flash drive. Because Disk Utility's cloning process must be able to see the image file, we must first copy the embedded image file to the desktop, where Disk Utility can see it without any issues.

Copy the installer image to the desktop

1. Open a Finder window and navigate to /Applications/.
2. Right-click on Install OS X Lion (this is the installer you downloaded from the Mac App Store), and select "Show Package Contents" from the pop-up menu.
3. Open the Contents folder.
4. Open the SharedSupport Folder.
5. Within the SharedSupport Folder is an image file called InstallESD.dmg.
6. Right-click the InstallESD.dmg file and select "Copy" from the pop-up menu.
7. Close the Finder window.
8. Right-click in a blank area of the desktop, and select "Paste Item" from the pop-up menu.
9. This will create a copy of the InstallESD.dmg file on the desktop.

Clone the InstallESD.DMG file to the flash drive

1. Launch Disk Utility, if it's not already open.
2. Click the flash drive device (not the volume name) in the Disk Utility window.
3. Click the Restore tab.
4. Drag the InstallESD.dmg from the device list to the Source field.
5. Drag the Mac OS X Install ESD volume name from the device list to the Destination field.
6. Make sure the Erase Destination box is checked.

1. Click Restore.
2. Disk Utility will ask if you're sure you wish to perform the restore function. Click Erase to continue.
3. You may be asked for your administrator account password; supply the necessary information and click OK.
4. The clone/restore process can take a bit of time. Once the process is complete, you can quit Disk Utility.

Using the bootable flash drive

To use the bootable flash drive as an OS X Lion installer, you need only do the following:

1. Insert the USB flash drive into one of your Mac's USB ports.
2. Restart your Mac.
3. When your Mac's screen turns off, hold down the option key while your Mac reboots.
4. You will be presented with the OS X Startup Manager, listing all bootable devices attached to your Mac. Use the arrow keys to select the bootable flash drive you created, and then press return or enter.
5. Your Mac will finish restarting using the flash drive. From there you can use the instructions in the following step-by-step guide to complete the OS X Lion installation:

Clean Install of OS X Lion