Mac OS X: create a bootable Mountain Lion USB disk

Prerequisites

1. A USB flash drive with as least 8GB capacity.
2. Install OS X Mountain Lion.app downloaded from Apple AppStore.(Or the InstallESD.dmg inside the app directory.)

Procedures

• Method 1: Use Disk Utility
  1. Right click the Install OS X Mountain Lion.app, in the context menu, select "Show Package Contents". In Contents/SharedSupport directory, you can find InstallESD.dmg
  2. Plug in the USB drive an launch Disk Utility, which is in /Applications/Utilities
  3. Select the USB drive in Disk Utility, activate the "Partition" tab,
     1. Partition Layout:1 Partition
     2. Format:Mac OS Extented(Journaled)
     3. Click Options... button, and set partition type to GUID Partition Table
     4. click Apply button to format the USB drive.
  4. Drag InstallESD.dmg into Disk Utitlity and select it.
  5. Activate Restore tab, drag the newly formatted USB drive into Destination field
  6. Click Restore button, it will start restore the image into the USB drive.
  7. NOTE: The whole process will take about half an hour. Right at the end, you might get an error message: "Could Not Restore - Invalid Argument". You can simply ignore it. The image should be restored to the USB drive successfully.
• Method 2: Use Lion Diskmaker
  1. Make sure your USB disk's partition type is GUID Partition Table, if not, re-partition your USB as described in Method 1 using Disk Utitlity. Otherwise, the disk made by Lion Diskmaker may not be able to boot.
  2. Download and run Lion Diskmaker
  3. Select Install OS X Mountain Lion.app then start making the disk.