SD card cloning using the dd command

I am trying to clone an SD card which may contain a number of partitions, some of which Ubuntu cannot recognize. Generally, I want to clone the whole volume, not only some partition. So, I mount the SD card and see something like this in the Log viewer:

kernel: [ 262.025221] sdc: sdc1 sdc2
alex@u120432:~$ ls /dev/sdc*
/dev/sdc /dev/sdc1 /dev/sdc2

Since I want to copy the whole disk, I execute:

dd if=/dev/sdc of=sdimage.img bs=4M

File sdimage.img, 7.9 GB (7,944,011,776 bytes) is created (SD card is 8 GB). Now I mount another SD card and execute:

dd if=sdimage.img of=/dev/sdc bs=4M

The problem is that the second dd command hangs on some stage, and never succeeds. After this, I cannot reboot or shut down computer, and I need just to switch power off.

Is this the correct approach? Maybe there is another way to clone an SD card?

OS: Ubuntu 12.04 (Precise Pangolin), 32 bit.

11

5 Answers

Insert the original SD card and check the name of the device (usually mmcblkX or sdcX):

sudo fdisk -l

You might see:

Device Boot Start End Sectors Size Id Type
/dev/mmcblk0p1 * 2048 2099199 2097152 1G c W95 FAT32 (LBA)
/dev/mmcblk0p2 2099200 31116287 29017088 13.9G 83 Linux

In my case the SD card is /dev/mmcblk0 (the *p1 and *p2 are the partitions).

Now you have to unmount the device:

sudo umount /dev/mmcblk0

Now to create an image of the device:

sudo dd if=/dev/mmcblk0 of=~/sd-card-copy.img bs=1M status=progress

This will take a while.

Once it's finished, insert the empty SD card. If the device is different (USB or other type of SD card reader) verify its name and be sure to unmount it:

sudo fdisk -l
sudo umount /dev/mmcblk0

Write the image to the device:

sudo dd if=~/sd-card-copy.img of=/dev/mmcblk0 bs=1M status=progress

The write operation is much slower than before.

4

You should not be using dd on mounted devices. unmount all the partitions first, then your command should work.

2

I am using dd tool to clone usb sticks with multiple partitions, here is my command:

sudo dd if=/dev/sdb of=/dev/sdc bs=4096 conv=notrunc,noerror

notrunc - do not truncate the output file
noerror - continue after read errors

1

dd is fine, but I prefer cat /dev/sdc/ > ~/backup.isoIf you want to put it on an SD card again, just run cat ~/backup.iso > /dev/sdc

1

Here are the steps which worked for me on Ubuntu to restore the image file (~/raspberrypi2.img in my case) back to a new SD card (inspired heavily by Alon's reply above):

1. Insert the micro SD card via the card reader.
2. Open the Disks app.
3. Quick format the whole card (not a specific partition).
4. Close Disks.

5. Open terminal and execute:

   sudo fdisk -l

Relevant output (which showed there were no partitions due to the quick format of the whole card):

Disk /dev/sdb: 7.4 GiB, 7948206080 bytes, 15523840 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x6957f2f2

---

sudo dd if=~/raspberrypi2.img of=/dev/sdb

This step takes a few good minutes (even on USB3). Make sure to not interrupt it by any operation which will invoke mounting (opening the Files or Disks apps).

Thanks for everyone's answers.