Create Disk Images on Mac OS With The dd Command

The procedure is as follows:

1. Open the Terminal app
2. Get disk list with the diskutil list
3. To create the disk image: dd if=/dev/DISK of=image.dd bs=512
4. To write the disk image: dd if=image.dd of=/dev/DISK

Let us see all commands in details.

1. Create disk image with dd command

Open the Terminal application and type the following command to list disks:

$ diskutil list

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

Here is what we see:

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

It will take some time, and you won’t see any updates on the screen. You can press the ctrl+t (hold control key and press t) to see dd command progress on macOS:

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

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

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’