There are many reasons why you may want to use a USB Flash drive to install Mac OS X Mountain Lion. If you need to install multiple copies on a few computers, or even prefer not to have to download a new copy every time you have to install the Mac OS. And from what I’ve experienced, installing from a USB Flash drive is faster than installing via downloading a new copy from the Mac App Store or even from DVD. Also USB Flash drives don’t scratch, DVDs do.
The steps necessary to create a Flash drive to install Mac OS X Mountain Lion are fairly simple. There are just certain parts that need extra attention however, I will highlight these areas.
Also check out: How to Install OS X Mavericks from USB Flash Drive
Step 1 of 3 – Preparation
Show Package Contents
Firstly you actually have to have the OS X Mountain Lion install app downloaded, you can purchase it from the Mac App Store. Once Mountain Lion has been downloaded, you’ll be able to find it in your Applications folder.
If the downloaded Mountain Lion app automatically pops up after downloading, don’t install it yet, just close the window. What we’re looking for is a DMG file. Go to your Applications folder and locate the “Install OS X Mountain Lion” app. Right click it and select “Show Package Contents”. Once opened there’ll be a folder called “Contents”, open it, and finally open the “SharedSupport” folder. Inside this folder there should be 2 files, one called “InstallESD.dmg” and the other “OSInstall.mpkg”, copy the InstallESD.dmg to the Desktop. This will be the file that we’ll be using to create the bootable disk image onto the USB Flash drive.
Step 2 of 3 – Prepare the USB Flash drive
Format USB drive
To create the bootable disk image, your UBS drive has to have at least 8GB of storage. Nowadays USB Flash drive are really cheap and can be purchased at almost any electronics store (the Flash drive I use is 16GB and only cost $15). Plug it into your Mac, and launch Disk Utility (located in Applications/Utilities). We’re going to format the USB drive, so make sure there isn’t anything on it that you need, as formatting will erase everything on the USB drive.
Select the USB drive that is to be formatted, then select the Erase tab. Under the selection for “Format:” select “Mac OS Extended (Journaled)“, and name it anything you’d like. It would probably would be best however to make it something recognizable like “Mac Install” or “Mountain Lion Installer”. Up to you though. Then simply press the “Erase…” button on the bottom right when done. The USB Flash drive will then start to format; in most cases it takes less than a minute.
If you don’t already have a USB flash drive, or want a USB flash drive that is already compatible with Mac OS X then you can purchase one from the MacMall. It’s a good place to buy Mac friendly stuff. Here’s an affiliate link to a 16GB USB drive that comes already properly formatted for the purpose of installing Mac OS X:
PNY 16GB Attaché 2 USB 2.0 Flash Drive – Black,Blue (P-FD16GATT2-GE) only $11.99.
For more information on formatting check out my other post: How to Format & Repair a Drive with Disk Utility
Step 3 of 3 – Restore Disk Image
Restore Disk Image
Once your USB flash drive has finished formatting, it’s time to “restore” the drive image. In Disk Utility select the partition that was just formatted and click the restore tab. Make sure to select the partition that you’ve created and not the drive itself. To elaborate, as you can see in the screenshot, I’ve selected the partition I named “Mac OS X Install ESD”, not the drive itself. If you select the drive instead of the partition, then it won’t restore the disk image onto your USB flash drive.
There are two input boxes. One labelled “Source:” the other “Destination:”.
For the “Source:” box either drag the “InstallESD.dmg” file in, or click the “Image…” button, navigate to your desktop and select “InstallESD.dmg”. The destination will be the partition you’ve created. Simply drag the partition that’s on the USB drive that you formatted into the “Destination:” box from the panel on the left of Disk Utility. Next simply press the “Restore” button on the bottom right.
This could take a while to complete, let it do its thing. Once the process is done, your USB drive is ready to go.
If you want to use the USB to format a new computer or re-format your current computer, there are 2 ways of getting it installed. One is to go to System Preferences -> Startup Disk -> and select the USB drive. This will load up the Mac OS X Mountain Lion installer as soon as you restart your computer. The other method is to simply hold down the Options key on the keyboard when your Mac is just turning on after being shutdown/restarted.
Once it’s done booting into the installer it’s a simple process of going through the provided setup steps (easy stuff).
Did you know you can run Mac OS X Mountain Lion from a USB Flash drive? Here’s how: Boot from portable USB disk
You can even boot from an old formatted iPod Classic, here’s a guide: How to Boot and Run Mac OS X from an iPod Classic
I tried to copy the install.dmg to the flash drive, but when i click restore it says the resource is busy and it wont work
April 15, 2013 at 5:00 pmI had the same problem and disconnecting and reconnecting didn’t work
April 22, 2013 at 10:03 pmCould you go into more detail? What steps did you take, the more descriptive the better I may be able assist you.
April 23, 2013 at 12:36 amif u just choose the usb drive and not the partition u will get this error
April 25, 2013 at 4:42 pmYou are correct Calle, when restoring the drive image the partition should be selected, not the drive itself. I should have been more clear about this. I’ll update the article.
Thanks.
April 25, 2013 at 11:54 pmcan i update this direct from my operating system Mac OS X 10.5.8
May 19, 2013 at 10:05 amUnfortunately no, OS X v10.6.8 or OS X Lion has to be installed in order to update directly from your operating system.
Here is some more information on Mountain Lion system requirements: http://support.apple.com/kb/HT5444
May 20, 2013 at 12:47 amI have a 32GB usb disk . I wish to have 2 partitions and use one partition to make Mountain Lion USB installer disk. 2nd partition for storage purposes. is it possible? Thanks
May 29, 2013 at 12:27 amYes.
May 29, 2013 at 12:43 amCan I install it from the flash drive without erasing all the data on my laptop? I’m doing this for Mavericks DP 1, but I’m still not sure about that. Thank you.
June 15, 2013 at 2:49 amYeah, it’s not a problem. In disk utility just create another partition on your hard drive, then install Mavericks on that partition.
June 15, 2013 at 2:51 amthanks! Good idea so it doesn’t messes up with my stuff, but is there a way to just install it on top of ML? Like you would do with the final release. I didn’t have this problem with the ML previews. I would just install them normally from the installer, but Mavericks isn’t letting me do that for some reason.
June 15, 2013 at 3:05 amNot to sure if you can install it over ML. And you may not want to use it as your main OS yet, it’s still in its first beta and very buggy. The partition method is currently the best choice.
June 15, 2013 at 3:14 amDid you try this? Same issue here but I don’t want to risk it
August 10, 2013 at 10:29 amthanks for the article! strange though it doesn’t work over here. After the 1. step erasing and creating a partition (extended journaled), the 2. step erases and formats the partitition as (just) exteded and is not recognized as a bootable drive. Any ideas?
June 17, 2013 at 5:42 amMy macbook pro mid 2010 13inch laptop’s hard drive is done. I don’t know why but a question mark folder pops up so I’m buying a WD hdd 2.5-inch 500gb 7500rpm and I want to install ML off a USB. If I buy it on an older mac and follow your instructions should I be able to install it on my new hdd?
June 22, 2013 at 12:34 amYup, you can install it on a new hard drive. Not a problem there.
June 22, 2013 at 12:39 amAfter choosing start up disk as mentioned by you , when I restart my mac I am unable to start mountain lion.please give me solution of this.
July 2, 2013 at 4:48 amAre all your other external devices removed?
July 2, 2013 at 12:05 pmI tried to restore ML on my corsair flash voyager USB 3.0 16GB and halfway through restoring i received an error saying that it unexpectedly shut down so i took out the usb then i tried to plug it back in then i get an error message saying that the flash drive is unreadable. So I plug it into windows and diskpart in command prompt says there is ‘no media’. What the F***? now my windows 8 laptop won’t detect my flash usb anymore.
July 3, 2013 at 11:46 pmIf you formatted the USB drive to Mac Journaled then it will no longer be recognized on Windows. This is just because Mac Journaled and Windows isn’t natively compatible. I’m not to sure what went wrong with during the process. However to fix the USB drive, just format it in Disk Utility again.
Also if you want to use it on Windows again, you’ll have to format it in Windows (NTFS).
July 3, 2013 at 11:53 pmthat’s the problem, my hackintosh snow leopard won’t even recognize the USB, and my windows recognizes it but won’t format it as it says there is no media present.
July 4, 2013 at 7:33 amIt may help to repair the USB flash drive in Disk Utility. Here’s an article about it: http://appducate.com/2013/02/how-to-format-repair-a-drive-with-disk-utility/
July 4, 2013 at 1:03 pmThe problem is that when I plug my voyager flash usb into my desktop, nothing appears in the mac desktop & I can’t see my flash usb in disk utility in snow leopard
July 4, 2013 at 3:54 pmI erased the contents of my hard drive because I am going to sell my MBA 2012. Afterwards, I tried reinstalling Mountain Lion (my laptop came pre-installed with Lion with a free upgrade to Mountain Lion) but I got an error “could not write installation information to disk” and now, I’m stuck with a flashing folder with question mark. I tried going into internet recovery (by pressing CMD+R) on boot but it’s getting an error as well. If I create a USB boot disk and insert it before bootup and press option, will I be able to fix my laptop? I’m currently stuck right now.
My laptop is already out of warranty, but I know it isn’t a hardware issue.
July 11, 2013 at 12:38 amHello arvbee. Yes, if you boot into a USB boot disk, you it be able to fix your laptop. Once booted into the USB stick, you’ll have access to Disk Utility and everything else you need to get Mountain Lion installed back on your Mac.
July 11, 2013 at 12:38 amThanks! Should’ve thought of doing it the USB way before I reformatted.
July 11, 2013 at 12:41 amWill I be able to create a USB boot disk if the laptop I’ll be making it on came pre-installed with Mountain Lion? Will the steps mentioned above work the same?
July 11, 2013 at 12:41 amYes, it shouldn’t pose any issue at all. Basically you’re just copying (mounting) the Mountain Lion disk images onto the USB drive. It doesn’t matter which version of Mac OS X you currently are using.
July 11, 2013 at 12:42 amhey, i have a mid-2009 macbook pro, i am about to upgrade my ram to 8 gb and upgrade my hdd to 1tb hdd. can i directly install mountain lion onto the new hdd since i alrdy own mountain lion in the mac app store? or do i need to install older version because i went to look at the older osx install disks sold by apple and it is over $100… so if i can directly install my owned mountain lion onto my new hdd that would be great.
thanks :)
August 5, 2013 at 2:42 amHey Kevin, you don’t need to buy a previous version of an OSX install disk. You can install Mountain Lion directly onto your new HDD. Once you’ve install your new HDD, restart and hold down the Option key. It will give you the option to boot into the USB drive, once the USB is loaded just have it install OS X onto your new HDD. Done.
August 5, 2013 at 10:04 amI alrdy have mountain lion on my current Mac how do I still mount the mountain lion file onto USB? I don’t have a install mountain lion app
August 7, 2013 at 12:05 pmDid Mountain Lion come pre-installed on your Mac or did you install it yourself. You can download the Mountain Lion app from the App Store, if you’ve already bought it once to install ML on your current Mac then you can just download it again for free.
August 8, 2013 at 12:49 amim a new user to mac so excuse me if my question sounds stupid. i have a flash drive with the “InstallESD.dmg” file on it and i am trying to install OS X Mountain Lion onto my mac. whenever i try to open the file on my macbook pro, it says “the following disk images couldn’t be opened” and the reason below “not recognized”. i hope you can help me. thank you.
August 27, 2013 at 3:04 pmDid you just copy and paste the InstallESD.dmg onto the USB or did you restore it onto the USB in Disk Utility?
August 28, 2013 at 10:05 amhaha yes i copy/pasted at first. i followed the steps this time but i got an error; Restore error, could not restore- invalid argument. i repeated the steps a few times and i got the same error.
August 28, 2013 at 10:27 amDamien, I have the usb all ready to go. My question is will this type of installation upgrade the OSX from snow leopard to ML, or will it completely do an erase and clean install? I only want to upgrade to keep all the other info I already have, and not lose it with an erase/clean install.
This is for an iMac and the strange thing is that when I try to install the good old fashion way I get the error “This disk cannot be used to start up your computer.” It only has the one hard drive that starts it up every time… hahaha! I have nothing externally connected. I have tried a lot of other ways to install, and have deleted the download and re-downloaded just in case I got a corrupted download file somehow. I have no apps running when trying and have also done the PRAM clear as a “well it can’t hurt.” It’s making my brain hurt, but it’s only a little pain as I only have a little brain…LOL
I look forward to your response and I hope this will get me going. Thanks!
September 30, 2013 at 12:10 amHey there Wallace, how old is your iMac? ML requires a Mid 2007 or newer iMac. Since you have Snow Leopard and not just Leopard you can upgrade to Mountain Lion. Are you running the latest Snow Leopard update? 10.6.8 I believe.
Also if you are just trying to upgrade without wiping everything you could just open and run the Mountain Lion file you downloaded from the Mac App Store. More info on that: http://www.apple.com/ca/osx/how-to-upgrade/
Another thing, when it’s referring to the startup disk it’s referring to System Preferences -> Startup Disk. Normally it would add the ML install file to the startup disk so that when your computer restarts, it would load up the installation instead of just going to your log in screen like it normally does.
September 30, 2013 at 10:58 amI tried to copy the install.dmg to the flash drive, but when i click restore it says the resource not found and it wont work.
December 20, 2013 at 1:14 pmHello, I have a question. I have a pretty big problem. I recently tried to intall Ubuntu on my imac, I only wanted it in a partion and not delete my Mac OS. The Ubuntu installation CD deleted everything and reformated my hard drive. I am trying to reinstall Mac OS but my computer no longer recognises my original Mac OS X install CD. So I found this site and am trying to create a start up USB, which so far isn’t working, but I am going to repair the USB stick and try again. But I was wondering if you had anymore information or a tip or way that I can finally get my precious Mac OS on my iMac again. Please help. Thank you in advance. Regards.
May 3, 2014 at 4:03 am