How to Boot a Mac from USB Drive

CD/DVD drives are disappearing from computers, leaving USB storage as the only option when re-installing an operating system. The process is fairly painless and, if you have a bit of time and patience you can complete the task on a Mac.

Steps

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    Download Mac Lion Installer from App Store. Latest versions of Mac are only available through App Store.
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    The download can take some time depending on your internet connection.     Don't worry if you lose connection halfway through download, it will resume as soon as you are re-connected to App Store.
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    Make a backup of the installer you downloaded from App Store and save it on your desktop. Under no condition should you work on the original installer file.
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    Use the backup file to make a bootable USB drive.
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    Right click (Two finger click) on the installer file and click on "Show Package contents".
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    This will open a new window with contents of installer file.
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    Navigate to Contents > SharedSupport.
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    You’ll see a disk image called “InstallESD.dmg.” This is your ticket to creating a bootable copy of OSX Mountain Lion.
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    Go to search icon and type "Disk Utility".
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    Click on "Disk Utility" Application and wait for it to open.
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    Drag the “InstallESD.dmg” file from installer folder into the white box on the left side of Disk Utility, and the disk image will be added.
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    Connect your USB drive to the Mac using the provided slots.
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    Wait for it to be recognized and displayed on the desktop.
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    Select the USB from the list in Disk Utility.
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    Click on "Erase."
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    Ensure it’s partitioned as “Mac OS Extended (Journaled)” under the “Partition” section in Disk Utility.
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    *The name will be "Untitled" by default, you are free to change it as per your liking.
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    Click on "Erase" in bottom right corner.
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    Wait for USB disk to be erased and restored to single clean and usable partition.
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    Click on “InstallESD.dmg” icon on the left side of Disk Utility app.
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    Click on "Restore" tab in the centre-top part of Disk Utility App. “InstallESD.dmg” should already be present in source tab.
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    Drag the drive you just added to Disk Utility from the source list in the top left of the app white space to the “Destination” path.
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    Hit “Restore” and let Disk Utility work its magic. This could take some time so please be patient.
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    Close Disk Utility. You now have a bootable USB disk drive with Mac OSX Mountain Lion installed and good to go!
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    Restart the computer you wish to boot from this disk.
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    While restarting, hold down 'option' key.
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    Select the Installer app from the menu and you will be able to boot from it.
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    Congratulations! You can now use this disk to verify/repair disk partitions, repair current installed OSX, upgrade to new OSX, or perform a clean install of existing or better OSX.

Tips

  • Always insist on original software as supplied by Apple Inc. and downloaded from Mac App Store.
  • There are some third party apps like "Lion Disk Maker" which specialize in creating bootable disk for Mac.

Warnings

  • A bootable Mac disk will work on Mac Computers ONLY.
  • Always backup your system using Time Machine before installing any new OSX.
  • Do not disconnect USB drive in middle of entire process.
  • Always keep a backup of your installer file before copying to USB/external drive.

Things You'll Need

  • 8GB+ USB external drive
  • Mac OSX Installer from App Store

Article Info

Categories: Mac