Documentation:

Writing an image to a USB stick or SD card on Mac OSXΒΆ

The instructions are the same, regardless of whether you write the image to a USB stick, or to an SD card.

If you are writing to an SD card, you can use your computer’s built-in SD card reader (if it has one), or use a USB adapter.

To write the image:

  • Determine the device name of your USB stick or SD card. That is easiest if you run:

    > diskutil list
    

    before you insert the USB stick or SD card, and then after. The device that has shown up is the device that you just inserted. For example, the device name may be /dev/disk8.

    Warning

    Make sure you get the device name right, otherwise you might accidentally destroy the data on some other hard drive!

    Also make sure your USB stick or SD card does not contain any valuable data; it will be mercilessly overwritten.

  • Depending on what’s on your USB stick or SD card, OSX might have automatically mounted it. To unmount:

    > diskutil unmountDisk /dev/diskN
    

    if the device name is /dev/diskN.

  • Determine the file name of the image you downloaded. Let’s assume it is ~/Downloads/ubos_yellow_pc_LATEST.img. If you downloaded a compressed version, uncompress the file first.

  • Write the image using dd, such as:

    > sudo dd if=~/Downloads/ubos_yellow_pc_LATEST.img of=/dev/rdiskN bs=1m
    

    replacing /dev/rdiskN with the device name of your USB stick or SD card. You can use either /dev/diskN or /dev/rdiskN (replacing N with the correct number), but /dev/rdiskN is 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.

    This may take 10min or longer, depending on the speed of your USB stick or SD card, so be patient.

  • When done, for good measure:

    > sync
    

    and wait for a little bit. Rumor has it some flash drives keep writing for some time after the OS thinks they are done. If that is true for your device, and you remove the device prematurely, you may end up with a corrupted image without a good way of telling that it happened.

Thanks to the Ubuntu project whose description helped when creating this page.