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Create Bootable USB Thumb Drive From ISO

Create bootable USB thumb drive from ISO imageHow to make a bootable USB thumb drive in Mac OSX from an ISO file

An ISO file or image is an archive file containing the exact contents of an optical disc such as a CD or DVD.  It includes the entire disc’s contents including the file system.

I’ve previously discussed converting DMG files to ISO files on your Mac.  A DMG is similar to an ISO in that it’s a mountable image.

Usually ISOs are used to distribute CD images such as distributions of operating systems such as Linux.  If you would really like to learn more about ISO files you can view this comprehensive Wikipedia page.

ISOs are not however limited to such uses and software is available to create your own ISO archives with just about anything on them.

One of the main advantages of an ISO is that because you are creating an entire image of a CD it takes everything with it including that CD’s ability to boot for example.

So if you normally boot from a CD such as your Windows XP CD or a Linux live CD then you can theoretically create an ISO image of these CDs and with the instructions below you can create a bootable USB thumb drive also which can be very handy in today’s netbook world.

Creating an ISO from a CD

You probably already have an ISO that you’d like to make a bootable thumb drive from but if you don’t, it’s quite easy to make one from a bootable CD on your Mac.

  1. Insert the CD
  2. Open Disk Utility
  3. In the left pane, highlight your CD/DVD drive
  4. On the toolbar, click New Image
  5. In the dialog box
    • In the Save As field enter a filename for your image
    • In the Image Format field, select CD/DVD master
    • In the Compression field, select none
  6. Click Save
  7. After about 10 – 20 minutes, the creation process will be complete.
  8. You will notice however that the file name ends with .cdr but you can change this to .iso by simply renaming the file.

Creating the bootable USB thumb drive

It is technically possible to create the bootable thumb drive using Disk Utility but for this I will show you how to do it the more reliable way (in my opinion anyway, but hey that’s why you’re here) using Terminal.

  1. Plug in your USB drive and wait for it to mount.  Make sure the capacity of the USB drive at least 1GB.
  2. We will be erasing the contents of the USB drive during this process so now is a good time to go ahead and copy anything you need off the USB drive
  3. Open Terminal
  4. Type the following and press enter:  diskutil list
  5. You will see a table of data.  This is a table of all the disks and volumes on your Mac.  Look for the disk path for your usb drive.  It will look something like /dev/diskx where x is the disk number.  I’m pretty sure it won’t be zero as that’s usually your hard disk.  In my case it’s /dev/disk2
  6. Type the following and press enter:  diskutil unmountDisk /dev/diskX (change X to the disk number of your USB drive)
  7. OK for this next step I’ll teach you a quick and dirty trick.  You must replace the letters YOURISOFILE with the path of the actual ISO you created in the previous section.  Instead of finding the path and typing it into Terminal simply do the following:
    • Type:  dd if=
    • Now drag your ISO file from your Mac’s Finder or Desktop or where ever you saved it and drop it on the Terminal window – no, I’m not crazy.  You’ll notice when you drop the file that the path of your ISO will be inserted nicely after the dd if= that you just typed.
    • Now finish typing the command:  of=/dev/diskX bs=1m
    • So the whole command you need to enter is:  dd if=YOURISOFILE of=/dev/diskX bs=1m
    • Remember to replace YOURISOFILE and diskX with your own values!!
  8. All set?  Press Enter and wait – mine took 71 minutes to complete.  When the process is finished you are returned to the Terminal prompt and hopefully you will have a bootable USB thumb drive.


Wow, 39 Comments! We've got a conversation going now. Join the discussion below!

  1. KR says:

    Tried this and it all completed fine. But when i stuck the USB drive into a new machine to install windows 7 from it onto a new drive , got this message “”DISK BOOT FAILURE, INSERT SYSTEM DISK AND PRESS ENTER.” I have changed by BIOS settings to boot from USB first.

    Trying to create a DVD from the iso now to see if that works..

    1. thutch says:

      I have the same problem. Tried with cd, dvd and usb to no avail! Please help.

      1. Ace says:

        Creating a bootable disk on a Mac is different for USB and CD. Thutch, if you are using a Mac, then use the Disk Utility to burn the ISO file onto your CD or DVD instead of the command line instructions listed above. Here are some instructions: https://lifehacker.com/251758/mac-tip–how-to-burn-an-iso-or-dmg-file-to-disc

  2. P Martins says:

    Hi there,
    every time I tried it I got this: “dd: /dev/disk1: Resource busy”
    What could be the reason?
    I’ve mounted and unmonted the pen drive several times.

    1. Rosco says:

      Hi there.

      Usually this indicates that the disk is in use somehow.

      Try this:

      Open Disk Utility, unmount any of the individual partitions on the pen drive but do not eject the pen drive itself.

      Now right click on the pen drive in Disk Utility and note the identifier from the information tab.

      Now go back to terminal and use the following:

      dd if=’your iso image’ of=/dev/’your identifier’ bs=1m

    2. Ace says:

      an alternative is to use /dev/rdisk1

  3. P Martins says:

    thanx for the quick answer but when I checked the Disk Utility there are no individual partitions to unmount on the pen… quite strange.
    Any ideias?
    Thanx again

  4. salman says:

    sir i have made bootable usb drive. but i want to know that how can i install windows xp on mac with it. because by dvd is finished.

  5. jake says:

    I got it copy all the file from ISO to my 4 G drive, no error , but when i option boot from Mac it didn’t show up at all,
    how do i make it boot from Mac…..

    1. Rosco says:

      Hi Jake,

      Insert USB stick, restart the Mac holding down the ALT (Option) key.


  6. john says:

    I’m a quasi-geek guy. I have several Linux machines and don’t mind using terminal. I tried this method to burn yellow dog to DVD (instead of thumb drive) to convert an old G5 to YDL. I get an error message telling me I don’t have permission! Any idea what went wrong?

    Great site. Thanks for your help and insights.

    1. Rosco says:

      Hi John…I presume you’re using Mac to burn it?

      If so, simply use Disk Utility instead of terminal for a DVD.

      If you prefer command line, you should use a utility called cdrtools (formerly cdrecord).

    2. raespl says:

      Sorry if it is too obvious: sudo ?

      It happened to me…

  7. Jake says:

    I did use option boot I only see systemdisk. The ISO file that I use can burn it to CD and boot it from MAC using without problem.

    In detail this iso file is to setup WinPE to connect SCCM for bootcamp.

    1. Anonymous says:

      you.. want to run WinPE on a PowerPC-based mac…? not going to happen : /

  8. Frensoa says:

    I tried this, but when I enter the last command, the Terminal tells me “dd: /dev/disk2bs=1m: Permission Denied”.

    Any clue why this is happening and how to fix it?

    (I’m completely new to Terminal…)

    1. Ace says:

      Make sure you add “sudo” at the very beginning, and then when you get prompted for the password. Just to be clear: enter in your password (not another user, or root/admin user).

      Sudo gives you temporary administrative/root level access. Since OSX is based on BSD, which is based on Unix, the entire operating system has user and group permissions and ownerships. Sudo gives you the ultimate ownership by taking on the identity of the root/admin user, so use carefully.

      1. npear says:

        still works with yosemite! nice to dig though the dust and cobwebs for little treasures to rebuild old systems.

      2. DeusExMachina says:

        This only works if the user is an admin, or is in the sudoers file, If they aren’t, they can’t use sudo, and MUST log in as an admin.

  9. Ray says:

    Hey, your guide was really useful and i was able to get it working. How do you make the drive back into a normal usb flash drive ? i’ve tried formatting but it still reads as cd drive on my computers. Help ?

    1. Ace says:

      You’ll need to partition the drive again. Use Disk Utility, select the thumb drive, select Partition. In Volume Scheme, in the drop down, select 1. In Options, select what you intend to do with the drive and click Apply.


      1. Ray says:

        Thanks for the lightning fast response. i’ve only just tried this now and it works like a charm. Consider your website bookmarked 8)


  10. samuel says:

    ace thank you for this guide but i am stuck on my mac when i insert my hard drive it boots up as a cd but when i restart while pressing option only my macintosh and recovery drive was seen please help

    1. Klaas says:

      Samuel, I have exactly the same problem. I just made a bootable usb drive using the command line above. But when I hold down the alt key it doesn’t show up (just the macintosh HD and recovery disk. Does anyone know how to fix this?
      great site though!

  11. Gerard says:

    I’m using an Acer Aspire One Netbook. I have complated these instructions on a MacbookPro.

    The Acer is not reading the bootable usb even after having changed the BIOS settings.

    I check to see the format of the USB and it is Mac OS extended, how do you complete the intsructions above but end up with a FAT usb?

    1. DaddyGeek says:

      You need to use Disk utility to make the partition into a FAT partition before you start. Also make sure under OPTIONS it is set to Master Boot Record.

      1. DeusExMachina says:

        For creating a bootable OS X install for a netbook, the drive needs to be partitioned as GUID, and formatted as HFS+ (Journaled), not MBR and FAT.

  12. Rocky says:

    After doing this to my usb, my usb does not show up when i plug it into my mac. is there a way to undo this?

  13. andy says:

    i type the code in with sudo dd if=
    it asks me for my password
    and then says operation not supported.. what should i do?

    1. Rosco says:

      Hi Andy….this message occurs if you have not unmounted the drive. Try step 6 again and make sure you’re unmounting the correct drive before you try the dd command.

      1. Andy says:

        when i try to unmount it, terminal says: disk 2 was already unmounted or it has a partioning scheme so use “diskutil unmountDisk”

  14. hi,
    this is michael from Empowering The Blind,, and I have a question related to your above directions. I am running these commands on Mac OS X version 10.8.3 system, and I don’t know if these commands are still valid. See the terminal code posted below.

    michael $
    diskutil unmountdisk /dev/disk1

    Unmount of all volumes on disk1 was successful
    michael $
    dd if= iso.iso of= /dev/disk1

    dd: no value specified for if

    the iso file i’m using is in /user/michael/desktop/isos/ and i’m in this directory already.
    thanks for any help.

    1. Anonymous says:

      You have to remove the spaces after the equal sign:
      dd if=iso.iso of=/dev/disk1

  15. Captivus says:

    71 minutes?
    If you want to improve transfer speed, you have to use
    # dd if=your_image.iso of=/dev/rdiskN bs=1m

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  20. DeusExMachina says:

    Just a quick note:
    DD will reformat the drive, destroying any partition scheme in the volume. If for whatever reason you need to maintain a given partition scheme, instead of using dd if=~/pathToFile.iso of=/Volumes/DiskX bm=1, one can specify the desired partition, e.g., dd if=~/pathToFile.iso of=/Volumes/Disk2s2 bm=1.
    Also if you are not in an admin account, one may need to use sudo, i.e., e.g., sudo dd if=~/pathToFile.iso of=/Volumes/Disk2s2 bm=1

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