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How do I create an MBR on a USB stick using DD command line tool

Jessica Young |

Okay I'm trying to create a BOOTABLE Windows7 image on a USB key from a Mac running Lion. My image is .iso format. I tried:

sudo dd if=/Users/myusername/Win7.iso of=/dev/disk1 bs=1m

And this succeeded in writing the files, except in DISK UTILITY on the mac, it shows the partition type as GUID Partition Table and not 'Master Boor Record'. Booting the key on my Vista computer yields the error "No boot sector on USB Device'

From what I can tell, bs=1m in the DD command should have left 1 Megabyte for the boot sector, but for some reason this area of the USB Key is not set up correctly so that it will boot

How can I fix this, or correctly use dd to write a bootable cd image such that it is now a bootable usb drive?

Note: in the instructions I read about, they recommended renaming my Win7.iso to Win7.dmg before using DD, which made absolutely no sense to me, so I didn't do it. I could try with that step now, but it takes 1.99 hours to write the image to the USB drive so there is a huge penalty to trial and error here. Thank you.

6

5 Answers

Use Disk Utility Options to set the partition type to Master Boot Record before you do dd.

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1

I had a similar problem when trying to create a bootable USB disk from OSX. The issue was that UnetBootin doesn't set up the Master Boot Record correctly on the USB disk. You have to do this manually with Disk Util and fdisk.

  1. Format the disk in Disk Utility, with the correct MBR

    1. Open Disk Utilty
    2. Select the USB device
    3. Click Partition
    4. Select 1 partition in the partition layout
    5. Select “Master Boot Record” in the options
    6. Select MS-DOS (FAT) in the format type.
    7. Click Apply, then Partition
    8. Close Disk Utility
      This will wipe the USB disk and set it up with the correct boot record

  2. Install the MBR binary from the SysLinux project

    1. Use the command line diskutil to find the device name for your USB drive. 
      diskutil list
    2. Unmount the USB drive with the command line. NB: Be sure to swap the device reference (in my case it is /dev/SOMEdisk2) with the correct one for your usb key that you identified in the previous step – this will change for each machine.
      diskutil unmountDisk /dev/SOMEdisk2
    3. Mark the partition active, then unmount it again 
      sudo fdisk -e /dev/SOMEdisk2
print
f 1
write
print
exit
      diskutil unmountDisk /dev/SOMEdisk2
    4. Download Syslinux and extract the mbr.bin file
    5. Install the MBR 
      sudo dd conv=notrunc bs=440 count=1 if=mbr.bin of=/dev/SOMEdisk2
      NB: see my full instructions if you need further help with steps 4 & 5.

  3. Use UnetBootin to install your OS install files

    1. Download and install UnetBootin if you haven’t already
    2. Load the application, choose your preferred distribution, and then click OK
    3. When it’s finished, eject the USB key and use it

Full instructions

7

Format a USB key with a Master Boot Record (MBR)

  • in Terminal: diskutil list

  • note the name of your USB key (mine was /dev/disk1)

  • in Terminal: diskutil eraseDisk MS-DOS "WINDOWS10" MBR /dev/disk1

  • replace /dev/disk1 with the name of your USB key

Mount a Windows 10 disk image

  • in Disk Utility: select File › Open Disk Image › select your .iso

  • in the left pane: click on the newly mounted image

  • in the right pane: select the name and copy it: something like CCSA_X64FRE_FR-FR_DV5

Copy the disk image to the WINDOWS10 USB key

  • in Terminal: cd /Volumes

  • in Terminal: cp -R CCSA_X64FRE_FR-FR_DV5/ WINDOWS10

  • replace the image name in the example with the name of your disk image

  • the slash at the end (after DV5 in the example) is important

  • it took more than 90 minutes to copy to a USB 2.0 usb key with, no progress indicator

1

This method doesn't use dd nor have I tested it.

You should be able to use UNetBootIn to transfer the filesystem in the ISO to a USB drive. UNetBootIn is an open-source, cross-platform utility for transfering bootable CD/DVD images to USB drives.

Run UNetBootIn (runs on Windows, Mac OS X and Linux) and select the Disk Image radio button. Then choose ISO from the dropdown menu (ISO is the default) and put the path to the ISO file into the path field. From there select the desired USB drive to transfer it to and click OK.

enter image description here

2

Just found an answer here

# fdisk /dev/sdY
create single partition type 7+bootable partition
# mkfs.ntfs -f /dev/sdY1
# ms-sys -7 /dev/sdY
# mount -o loop win7.iso /mnt/iso
# mount /dev/sdY1 /mnt/usb
# cp -r /mnt/iso/* /mnt/usb/

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