Since the release of Mac OS X 10.7 Lion, OS X has been only available via download from the Mac App Store.  Many users like to be able to boot from an installer device to do a clean installation of the new operating system.  You can easily create a bootable Mac OS X 10.8 Mountain Lion installer flash drive using the instructions below.

To create your own bootable USB device using your own flash drive (note that the device must be at least 8GB or larger), follow the instructions below.

1) Purchase and download Mountain Lion from the Mac App Store on any Mountain Lion compatible Mac running Snow Leopard or Lion.  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”

Show Package Contents


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



4) Copy InstallESD.dmg to another folder like the Desktop.  To do so, simply click and drag the file to the desired location while holding down the Option key.


5) Plug in the flash drive and launch Disk Utility (/Applications/Utilities).


6) Make sure the flash drive is properly formatted highlighting the flash drive at the left (make sure to select the device and not the volume shown under it) and clicking the Erase tab across the top right.  Then ensure that the Format drop-down menu is set to Mac OS Extended (Journaled) and click the Erase button.  Confirm the dialog ensuring that you want to erase the device and all information on it (make sure you backup any existing information on the flash drive before this point).

Disk Utility Formatting


7) Select the Partition tab on the top right.

Creating Lion Installer Partition

Using the drop-down menu for Volume Scheme, choose 1 Partition as the partition scheme.

Choosing Number Of Partitions

 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.  Select GUID Partition Table and click OK. This will allow the Mac boot from the drive.

GUID Partition Table

You may now name the device in the Name textbox. Insure that Format is set to Mac OS X Extended (Journaled). When you have finished, click the Apply button to format the USB device.  A warning will pop-up asking if you are sure you want to partition the media.  Click the Partition button to continue.

Formatting The Flash Drive


9) Click on the newly created volume listed under the USB device on the left. This volume will have the name of the device you set in the previous step.  Click the Restore tab at the top right.  In the Source area click the Image… button. Select the disk image InstallESD.dmg and click open (you may also drag-and-drop the disk image into the Source area).

Restoring Image To Disk

In the Destination area, make sure that the USB device’s name is showing. If it isn’t, simply click and drag the volume from the list at the left into the destination area.  Click Restore and confirm the dialog informing you the volume will be erased.  You will be prompted to enter the admin password for your Mac and the process will begin.

Restoring Erase Contents Warning

The bootable USB device will be created and a progress bar will show the current status of the operation at the bottom of the screen.

Restoration Progress Bar


10 ) When the operation is complete, you can verify that the flash drive is now bootable by selecting it and clicking the Info button in the upper left corner of the Disk Utility window.  Bootable status will show as Yes.

Bootable Flash Drive Information


To boot from the USB device, simply hold down the Option key while your Mac is booting up. A screen will appear asking you which volume you would like to boot the system from. Click on the OS X installer USB drive and the system will boot using the USB stick. You will see faster boot speeds using the USB installer compared to a DVD installer disc.

Instructions for creating a bootable Mountain Lion Installer DVD can be found here.


  1. Peter Ainsworth

    Clear and concise and correct

  2. Hi colleagues, good post and pleasant urging commented here, I am really enjoying by

  3. Hello, im having trouble finding the Shared Support Folder under Contents. Please let me know where i can find this

  4. Worked like a charm for MAC OS X 10.8 Mountain Lion. I got an error saying invalid argument when the restore was completed, but everything else still checked out and it booted from the USB drive just like you said it would. Thanks for the great guide!

  5. I need some help– i’ve followed all of the steps above but at the very end of the process receive this error message: ” Restore Failure — Could not restore — Invalid argument” from Disk Utility. However all prior steps worked perfectly.

    Not sure where to go from here so any direction would be great. Thanks!

  6. Thank you very much, in spite of my deficient english language I succeeded, that means you have been really clear !

  7. And I was looking for some external program for this job. Didn’t know that it’s hiding in my own system. Thanks a ton dude!

  8. John Canty

    Worked flawlessly At the end of the restore process I got an error, using an 8Gb flash drive. The error was an ‘invalid argument.’ I decided to go ahead and try to use it to install on my MacBook Air and it worked despite. In order to avoid this error, a larger sized flash drive may be necessary.

  9. Excellent tutorial, I’m a windows guy and I was trying to update the wifes Macbook. Very well written instructions. Worked perfectly! Thanks so much!

  10. Josh from Arkansas

    Worked great, very concise and to the point! Thanks for taking the time to educate us all! Blessings to you!

  11. The invalid argument error comes from naming the general drive in your destination window under the restore step. You need to specify which partition – the specific name you assigned it when you partitioned – which you are writing to in the destination field – and not the general flash memory’s name.

  12. many thanks for doing this! easy to follow & worked perfectly.

  13. Anonymous

    If i boot this on my school computer will i still be subject to the firewalls/ adminastrator controlls

  14. Ken Martin

    Really clear and well done! But is there a way to update what is on the thumb drive?

  15. Thank you for this post. Your instructions contained the right amount of detail. Very helpful!

  16. Thanks for a marvelous posting! I truly enjoyed reading it, you can be a great author.

    I will ensure that I bookmark your blog and will eventually come back in
    the future. I want to encourage you to continue your great work, have a
    nice evening!

  17. I own a new iMac, and was trying to do the same WITHIN the Mac, by starting up from the Recovery partition in the Mac…. I bought a 32 GB PNY compact flash drive (half the size of their regular drive, but it was 1/2 price at Best Buy), did the formatting, no partitioning, and started the process…

    The process took some 5 hours (which is normal, comparing to doing the same thing, making my ext. HD into a bootable drive), but when I went to boot up using the flash drive it took about an HOUR for the Desktop to show up, and even then, my HD won’t show as mounted on the Desktop…

    …Any clues?

  18. Thankyou so much, this has really helped me out!! The steps were very easy to follow!! Will forward the page on to any one who needs help like i did!

  19. Do i need a valid apple license that has previously purchased mountain lion? i am upgrading from leopard to lion

  20. Andre K.

    Thanks a lot, mate! Great post! Just what I needed. :)

  21. Drew Steel

    I select which disk to boot from and keep ended up at the disk utility. What do I do from here?

  22. Melanie Davenport

    Thank you so much! This article was clear, concise and super-easy to follow — all evidence of superior technical writing skills!

  23. Hi guys,

    I did all steps, but I get a error message “Could not restore – Resource Busy”

    Any ideias? Please, help me.

    Thanks, Felipe

    • Hello Felipe,

      Launch Disk Utility, unmount the USB drive volume (make sure you unmount the volume, and not eject/unmount the drive) and try again. It should allow you to restore this time.


  24. I enjoy what you guys are usually up too. Such clever work and reporting!

    Keep up the fantastic works guys I’ve included you guys to my blogroll.

    my website; e deklaracje

  25. Jim Clark

    Followed directions and got a bootable drive for my MBA running 10.8.4. Now how do I get Diskwarrior 4.4 to work from it? I installed DW onto the flash drive in same partition as System but DW was not available after booting.

    • You may want to contact Alsoft for installation issue. We have not tried DW 4.4 here and therefore will not be able to trouble shoot or comment.

  26. i tried all, unibeast, iboot, nothing worked, so thanks a load, it was there all the time, great stuff, nice. deejay.

  27. Your way of describing the whole thing in this post is truly good,
    all be able to easily know it, Thanks a lot.


  1. MilCom » Blog Archive » Great article on making a bootable OSX install image - [...] Here is the article: [...]

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