Creating a bootable USB stick from OSX

Published on January 9, 2013

I was having some trouble getting my ML110 Proliant lab server to boot from a USB drive that I had created with UnetBootin on my Mac. Initially, I thought it was a problem with the ML110 server, but it turns out that Unetbootin does not currently make a fully bootable USB stick in OSX. The trick is that you have to set up the master boot record correctly yourself using DiskUtil, fdisk and an MBR file from the SysLinux project. In this tutorial I will show you how.

If you would like to create a bootable USB drive from OSX, you will need:

Step 1 - Format the disk in Disk Utility, with the correct MBR

Assuming you have already inserted your USB drive into your Mac…

a) Open Disk Utilty

b) Select the USB device

c) Click Partition

d) Select 1 partition in the partition layout

e) Select "Master Boot Record" in the options

f) Select MS-DOS (FAT) in the format type.

g) Click Apply, then Partition

h) Close Disk Utility

This will wipe the USB disk and set it up with the correct boot record.

Step 2  - Install the MBR binary from the SysLinux project

Open up a terminal and then

a) Use the command line diskutil to find the device name for your USB drive.

diskutil list

a) Umount 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

b) Mark the partition active, then unmount it again

sudo fdisk -e /dev/SOMEdisk2
print
f 1
write
print
exit

diskutil unmountDisk /dev/SOMEdisk2

c) Download Syslinux

mkdir -p ~/Documents/BootableUSB
cd ~/Documents/BootableUSB
curl -L -O http://www.kernel.org/pub/linux/utils/boot/syslinux/syslinux-5.00.zip
unzip syslinux-5.00.zip -d syslinux-5.00
cd syslinux-5.00/mbr

d) Install the MBR - NB: Update the device name (/dev/SOMEdisk2) to the one you identified in the first step!!!

sudo dd conv=notrunc bs=440 count=1 if=mbr.bin of=/dev/SOMEdisk2

Step 3 - Use UnetBootin to install your OS install files

a) Download and install UnetBootin if you haven't already from http://unetbootin.sourceforge.net

b) Load the application, choose your preferred distribution, and then click OK.

c) When it's finished, eject the usb key and use it!

References

Thanks to a tip I found on http://perpetual-notion.blogspot.co.uk/2011/08/unetbootin-on-mac-os-x.html

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