Making a bootable USB key from an .iso image on OS X

To create a bootable USB key from an .iso image on OS X so that a machine with the ability to boot from USB keys can boot it, you need to first create an .img file from the .iso file you downloaded.

Tip: Drag and drop a file from Finder to Terminal to ‘paste’ the full path without risking typing errors.

Open the Terminal and type the following command to convert the .iso file to .img using the convert option of hdiutil e.g.,

hdiutil convert -format UDRW -o ~/path/to/target.img ~/path/to/downloaded.iso

Note: OS X tends to put the .dmg ending on the output file automatically.

Run

diskutil list

to get the current list of devices.

Insert your flash media.

Run

diskutil list

again and determine the device node assigned to your flash media (e.g. /dev/disk2).

Run

diskutil unmountDisk /dev/diskN

(replace N with the disk number from the last command; in the previous example, N would be 2).

Execute

sudo dd if=/path/to/downloaded.img of=/dev/rdiskN bs=1m
  • Using /dev/rdisk instead of /dev/disk may be faster
  • If you see the error dd: Invalid number ‘1m’, you are using GNU dd. Use the same command but replace bs=1m with bs=1M
  • If you see the error dd: /dev/diskN: Resource busy, make sure the disk is not in use. Start the ‘Disk Utility.app’ and unmount (don’t eject) the drive
  • To see progress you can type ctrl-t

Run

diskutil eject /dev/diskN

and remove your flash media when the command completes.