How To Create Disk Image on Mac OS X With dd Command

Posted on in Categories , , , last updated October 18, 2015

How do I create or write to images to disk on Apple Mac OS X Unix operating system with dd command?

You can use dd command to:

  1. Create new disk images from USB or SD card
  2. Write images to disk or USB or SD card

You also need to use diskutil command manipulates the structure of local disks including listing and unmouting disks before you create or write images to disk. Please be careful when running the following commands, as you might destroy important data or disk.

1. Create disk image with dd command

Open the Terminal application and type the following command to list disks:
$ diskutil list
Sample outputs:

Fig.01: Insert in your SD card, or USB pen/HDD, and see  /dev/diskN name
Fig.01: Insert in your SD card, or USB pen/HDD, and see /dev/diskN name

In this example my SD card size is 4GB and located at /dev/disk2.

2. Unmount the disk

Unmount the disk called /dev/disk2:
$ diskutil unmountDisk /dev/disk2
Sample outputs:

Unmount of all volumes on disk2 was successful

3. Create the disk image with dd

Finally create the disk image of the entire disk /dev/disk2:
$ sudo dd if=/dev/disk2 of=backup.my.sdcard-18-oct-2015.img.dd bs=512
OR
$ sudo dd if=/dev/disk2 of=backup.my.sdcard-18-oct-2015.img.dd bs=1m
OR
$ sudo dd if=/dev/disk2 of=foo.bar.img.dd bs=64k
Sample outputs:

Password:
60504+0 records in
60504+0 records out
3965190144 bytes transferred in 839.664927 secs (4722348 bytes/sec)

You can create compressed disk image as follows:
$ sudo dd if=/dev/disk2 bs=64K | gzip -c > backup.disk.img.dd.gz
Where,

  • dd : Command name
  • if=/dev/disk2 : Input disk name
  • of=backup.my.sdcard-18-oct-2015.img.dd : Output image name
  • bs=64k or bs=1m or bs=512 : Set both input and output block size to n bytes.
  • gzip -c > backup.disk.img.dd.gz : Create compressed disk image using gzip

You can verify your disk with file command:
$ file disk-name-here.img.dd

disk-name-here.img.dd: x86 boot sector; partition 1: ID=0xc, starthead 130, startsector 8192, 114688 sectors; partition 2: ID=0x83, starthead 165, startsector 122880, 6277120 sectors, code offset 0xb8

How do I write dd images to disk again?

The syntax is as follows:
$ diskutil list
$ diskutil unmountDisk /dev/disk2
$ sudo dd if=backup.my.sdcard-18-oct-2015.img.dd of=/dev/disk2
### Restores compressed image and write /dev/disk2 ###
$ sudo sh -c 'gunzip -c backup.disk.img.dd.gz | dd of=/dev/disk2'

See dd(1).

Not a fan of command line?

You can use ‘Disk Utility’ GUI tool to create and restore images. First ‘Open Disk Utility’ by visiting the Applications > Utilities folder:

Fig. 02: Disk utility in action
Fig. 02: Disk utility in action

Choose File > New > Image from “Untitled”. Next, enter a name for the disk image, then choose where to save it:

Fig.03: Saving SD card image
Fig.03: Saving SD card image

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin and a trainer for the Linux operating system/Unix shell scripting. He has worked with global clients and in various industries, including IT, education, defense and space research, and the nonprofit sector. Follow him on Twitter, Facebook, Google+.

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11 comment

  1. This is great. But in you GUI example, you left out how to write the image to say a flash drive. My problem is simple. How do I copy a Bootable MaxOSX flash drive to another MacOSX flash drive and it remain bootable. Can that be done in the GUI?

    1. Exactly, I need to copy a Mac Disk Image on a hard drive to a flash drive. With the “restore disk image” function completely omitted or hidden in the new and (ahem) “improved” disk utility, I am completely dead in the water with a Mac I am unable to resurrect. I found this article unhelpful and incomplete. Does ANYBODY out there know how to fashion a quick tutorial to accomplish this and be both thorough and comprehensive UNLIKE this article? Please? Anyone?

      1. Try out ApplePi-Baker
        Its a simple GUI based tool to create / flash images of disks and works with pretty much all file systems etc and its so easy to use!

  2. Howdy. I just ran this command: sudo dd if=/dev/disk5 of=/dev/disk1 bs=131072

    It asked me for my password and I entered it and then the cursor moved down to the next line and stayed there.

    Does that sound right? Is it frozen or just working? Is there no progress indicator?
    Thanks!
    C

    1. That’s correct, there is no progress indicator. If you really want you can quiz the process it runs in, in a seperate terminal but there really is no need.

      Just leave it go, it can take a while depending the same of the image you are moving.

  3. Is there a way to create the image to only use the “used” part of the disk you are copying? I have a 126 gig sd card that I want to flash to another card but the used area is very small. To restore the 126 gig image looks like it will take another 38 hours.

  4. If you use the “dd” command with rdisk instead of disk, the cloning will be 20x faster.

    e.g.:
    dd if=/dev/disk2 -> dd if=/dev/rdisk2
    dd of=/dev/disk2 -> dd of=/dev/rdisk2

  5. My External HDD restored from spindle problem, now shows larger volume. The actual size is 1.5Tb it is showing 4.1Tb. It doesn’t mount automatically, shows in disk utility. Can’t erase or repair or format using disk utility gives “Cannot allocate memory” or “Resource busy” error.
    Tried all of the above dd commands, gives “Resource busy” error when used the command with gzip, otherwise gives “/dev/destination drive/foo.img: Not a directory” error. The unmount using dd was successful.
    Most ‘free’ or open source disc recovery softwares have no luck recovering or properly scanning this disk.
    Does anyone got any idea what could be the problem?

  6. Hi
    $ sudo dd if=/dev/disk2 of=foo.bar.img.dd bs=64k
    I have always seen if=iso file and of=target disk. why in your example this is other way ? i’m confused. Have i missed something ?

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