How to make a bootable Mountain Lion USB install drive

Make a bootable USB drive Install of Macbook Pro OS Mountain Lion.

This is the process I used to make a bootable USB drive of the Mountain Lion Operating System on my Macbook Pro. My Macbook was the Macbook Pro 13″ inch 2012 model. This process for making a boot drive can work for other Macbook types too.  Difficulty rating 2/10, maybe even 1/10, super easy!

This is the process I used to create a bootable USB drive of Mountain Lion OS X for my Macbook pro.

Why Make A Bootable USB Install Drive for Mac Mountain Lion OS?

The main reason to make the bootable USB drive is to not have to download the 4GB file every time you want to do a reinstall of the Mountain Lion operating system.

The second reason to make a bootable USB OS drive is it makes reinstalling the operating system faster.  Using a USB drive method without the downloading makes a full reset take 30 minutes.  Without the USB drive it will take hours.

Tools you will need:

  • Macbook Pro. I have not tested this with other Macs, it should work 9/10.
  • Internet Connection to download the 4GB Mountain Lion install file from Apple.
  • OS DOWNLOAD USB DRIVE. 12GB or more USB Flash Drive. I used a 32GB USB drive, 12GB is the minimum amount of Geebees you need. More is okay, like 32GB is fine.
  • OS BOOT USB DRIVE. Optional 8GB or more Flash drive for a permanent USB drive, or you can reuse the OS DOWNLOAD DRIVE. This is optional because you can copy the files onto your hard drive and then on to the OS DOWNLOAD USB flash drive again whenever you need it. I used a separate 8GB USB Flash drive for my OS BOOT DRIVE to keep a permanent solution. I got my 8GB USB drive from Ebay for $6.

No extra Mac software is required to make or use the USB boot drive method.

Preparing the USB drive

Turn the Macbook pro ON. Insert the OS DOWNLOAD USB Flash Drive into the Macbook Pro.

Open the Disk Utility Program. (Hold the CMD key and press space bar -> Type “disk utility” without the quotes -> select disk utility from the list that is shown).

Now we will partition the OS DOWNLOAD USB drive and make it bootable. In disk utility, select your OS DOWNLOAD drive on the left panel by clicking on it. Make sure you click on the part of it that is most to the left on the left panel. Not the sub heading of it, the main heading. The main part that might say something like “28.36 GB NAMEOFCOMPANY”.

Now in the big panel on the right choose partition at the top, it should be the middle tab, between Erase and RAID. If you do not see the option to partition you did not click the correct drive on the left or clicked the sub heading. Make sure you clicked the main entry for the Flash drive.

In the partition area first click on the “choose” above the big box (in the “volume scheme” area) and change it to “1 partition”. Then click options just below this box and select the GUID partition table option, then click OK.

Now on the right of this area enter a name for your drive, like “OS X Installer” and change the format to “Mac OS Extended (Journaled). When you’re happy choose Apply and agree to the question that asks if you are happy to erase the Flash drive. Check to make sure it is the correct drive before agreeing! I am not responsible for your mistakes here!

Once it is complete you will have a clean USB drive ready for the Lion Operating system download.

End of formatting and partitioning the OS DOWNLOAD USB drive procedure.

Downloading the OS Install Files From Apple

Now with the formatted and partitioned OS DOWNLOAD USB DRIVE inserted shut down the macbook pro. Once the Macbook pro is off hold the CMD and r keys. Now turn on the Macbook pro while keeping hold of the CMD and r key. This will activate the Macbook Pro restore feature.  Every Macbook Pro has this feature to reinstall the operating system at anytime.

Once it has loaded, release the CMD+r keys and choose the second option – “Reinstall Mac OS X”, and hit continue. Now it will ask for verification through your internet connection. Agree to this and select YOUR USB FLASH DRIVE AS THE LOCATION to install. This is important because we want to download the files from Apple onto our USB drive.  Once you agree, it will start the download.


Once the download is complete you must pull out the USB Flash drive as soon as the black screen shows. If the screen is black, pull out the flash drive! Don’t wait, just pull it out. If you wait it will start the installation and delete the files from the USB and you’ll have to do it all again. You need these installation files to create a bootable USB Lion drive.  So, once the timer is close to 0 BE READY.  A few seconds after the timer goes to zero seconds remaining the the screen will turn black.  Remove the USB at the black screen!  Not before, and not after.


You pulled out? great. Now you have a USB Flash drive with OS Mountain Lion! That was the hard part completed, now the easy stuff.

Keeping the OS DOWNLOAD USB drive OUT of the Macbook pro and start the Macbook. It will load as normal. Press CMD+SPACEBAR and type “disk utility”, then select disk utility from the list. Now insert your USB drive with the operating system on it. Copy all the files from it to any location on your hard drive. I copied them into the Download folder, but you can put them anywhere you like.

Now open the folder you copied onto your hard drive. Look inside and you will find a big 4GB file ending in .dmg. This is the main file you need.

Insert your OS BOOT USB DRIVE. You should have already partitioned this drive, with a GUID and with “Mac OS Extended (Journaled)”. Use the usb guide above to do this.  If you are reusing your OS DOWNLOAD DRIVE partition and format it again using the above procedure once you have copied the operating system folder to your hard drive (we just did this in the last paragraph!).

Click on this big .dmg file to open and it will mount the .dmg file. Now go back to disk utility. You should have your OS BOOT USB DRIVE attached to your Macbook Pro and you will see the “InstallESD.dmg” file shows as mounted at the bottom of the left panel of disk utility.

Click on the InstallESD.dmg file on the left. At the top of the right pane choose “restore”. It shows two area you need to enter. Source and Destination. Source should already be filled with InstallESD.dmg. If it is not, then enter that now by browsing to the big file and inserting it into the Source box.

For the destination we want our BOOT USB DRIVE. So drag and drop that from the left panel to the Destination part.

When you are happy click the restore button to start the restore process. This takes around 30 minutes. Once complete you have your complete USB BOOT DRIVE!


To use the USB boot drive on your Macbook Pro, first insert the drive into the Macbook. Then shut down, or restart the computer. As it is turning on hold down the ALT key. This will show a special screen allowing you to select a startup disk drive. Select the USB drive (it is usually orange). The Macbook will shut down and restart using the USB drive as the Boss.

There was a problem installing Mac OS X, try reinstalling. If you get this error you will need to zap PRAM.  This sounds bad, but it’s nothing really.  Simple instructions for zapping P RAM below.

To zap PRAM shut down the Macbook Pro. Now hold down CMD+OPTION+p+r and turn on the Macbook Pro. OPTION is the “Left ALT” key and has a small bird symbol. It is near the CMD key on the left of a Macbook Pro keyboard.

When you turn on the Macbook Pro with the above keys held it will quickly reset and the screen will go to full brightness. This is the indicator that the PRAM has been cleaned. The PRAM holds simple hardware variables, like brightness level and it’s a safe procedure recommended on the Apple website. I take no responsibility if any of the advice here or on this website damages anything! I have completed every step here myself and have no fear doing it again, it is safe as far as I am concerned.

After zapping the PRAM insert the Installer USB Flash Drive into the Macbook Pro and turn off. Then turn on again while holding the ALT key on the left of the keyboard. Yes, just the ALT key and nothing else. The ALT key is near the Cmd key which is on the left of the space bar. Just hold this ALT key and start the Macbook Pro.

When it starts it will show you some hard drive options. Choose the orange Hard drive that represents your USB drive. Click it and it will take you to the install Lion screen. Now just follow the simple instructions to complete the installation of Lion! It takes about 8 minutes to prepare installation and 35 minutes to complete the installation process itself. You Macbook Pro will restart when the process is complete.

Congratulations! You have used a Bootable USB Flash Drive to Install Mountain Lion OS X. You can now repeat this process at any time to reinstall OS X on your Macbook Pro without needing an internet connection.  This process can work for other Macbook Pro versions too.

Leave a comment below if you found this guide useful or want to clear anything I missed, thanks :)

This is the end of the guide on how to make a bootable Mountain Lion USB Install Drive.

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19 Responses to How to make a bootable Mountain Lion USB install drive

  1. Thanks for the tip about the PRAM.
    Never would have entered my mind.
    Without this integral step, the USB install just causes great pain.

  2. Oh Boy, you saved me! You are the only article I found on the internet talking specifically about the issue of not being able to proceed with the installation of Mountain Lion 10.8.2 due to message errors. I tried and tried until I thought almost I had to bring my iMac to Apple store, until I saw your post. It was the PRAM. Followed your instructions and worked like a charm.

    Thank you from London town. CF.

  3. Thanks for the PRAM tip! That was my obstacle.

  4. Thanks a million … worked great.

  5. Malcolm Derrick

    Hi, when I try to copy the “installESD.Dmg” from source to destination (USB stick) it starts off fine then towards the end an error message says “restore failed” and something about an argument. Any suggestions?


    • Did you format your USB stick to journal extended? Is the error a show stopper? If the file still copied over it should be okay (test first!).

      If it is a show stopper, I recommend starting again and following the instructions exactly. Also, zap the PRAM.

  6. Malcolm Derrick

    You are correct, the files were on the stick and, after zapping p ram, it has started and using stick to reinstall. Thanks very much?.

  7. How to remove Bootable OS X Mountain Lion USB Drive from Flash?I have 16gb flash but don’t know how to remove Bootable OS X Mountain from my flash. Please help.
    Thank you.

  8. Dood!!, thanks big time!!, this was the answer I was looking for!!. Rock on!! \m/!!.

  9. Awesome, i was wondering why i kept getting that reinstall issue, thanks for the pram reset. I had to reset the pram for a different issue the other day as well. Apple needs to make all os releases via usb, as much as i like the app store, the usb is crucial for us nerds for various issues.

  10. Hey, thanks. Worked like a charm on MacBook Pro. I couldnt get beyond the “Try reinstalling” error message until I did the PRAM trick.

  11. You have been a great help, resetting the PRAM solved my problem that I couldn’t find solution else where. Thank you very much.

  12. My HHD went bad so I pulled it completely out of my MacBook and wanted to try and run Lion from a USB drive. I also have a MacBook pro and used it to help. I installed it and everything seemed perfect until the end when it said, Must have a recovery drive. Can I create a partition or use a small separate flash for this, can you run a Macbook strictly from a USB flash drive when there is no drive in the computer? It seems like there has to be a way right?


    • You can run a macbook from an external usb drive (and thumb drive). I do this. Try holding the left ALT or option key when starting up, then select the drive you want to boot from.

  13. SoHeL Ahmed sarkar

    Thanx bro, for ur time to give maximum details of the process. It helped me a lot….

  14. THANKS ,this is the best tutorial for instalation error.

  15. So how to.