Last week, I explained how to reinstall Lion/Mountain Lion by using the recovery partition to resolve software issues or to wipe and install a clean version of the OS. Those solutions rely on a fast internet connection that allows a download of the OS.
A worthy thing to have in your tool box is a bootable USB installer just in case you cannot connect to the internet. It comes handy if you want to upgrade or install Mac OS on multiple personal machines or if you have done a hard drive replacement or upgrade. You would need a bootable installer because the recovery partition would not be available on the new drive.
To make a Bootable USB stick you need:
- One USB drive with at least 6GB of free space
To create the Bootable USB stick follow these steps:
Acquiring the OS
- Purchase & download Mountain Lion
- Quit the installer with Command+Q when the download is finished
Finding the Installer
- Navigate to the Applications folder
- Locate the Mac OS Installer in the Applications folder
- Control+click the file
- Select Show Package Contents from the contextual menu
- Navigate to Contents > Shared Support
- Locate a file named installESD.dmg
Creating the Bootable USB Stick
Warning: All data on the flash drive will be erased in this process.
- Launch Disk Utility (located in Applications > Utilities > Disk Utility
- Drag the installESD.dmg file to the white space in the lefthand sidebar
- Insert your USB stick into an available USB port on your Mac
- Select the USB stick from the lefthand sidebar
- Partition the USB stick with the following settings: Format: Mac OS Extended (journaled) & Options: GUID Partition Table
- Select the Restore tab
- From the lefthand menu drag the installESD.dmg to the Source field
- From the lefthand menu drag the USB stick to the Destination field
- Click Restore
This process can take 15-30 minutes. Once completed, you have a bootable USB installer.
To boot from USB, hold down the Option key when the machine is booting up before the first chime and select the USB installer.