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Alex F
Asked: 2012-12-12 05:42:36 +0800 CST

SD card cloning using the dd command

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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.

sd-card

5 Answers

  1. 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.

    • 71
  2. Best Answer

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

    • 41

  3. 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

    • 16

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

    • 11

  5. 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.

    • 1