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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.

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Can you mount created img file and see if it is created correctly? – Milan Todorovic Dec 11 '12 at 14:40
@MilanTodorovic - how can I do this? – 0123456789 Dec 11 '12 at 15:15
If I remember correctly: mount -o loop sdimage.img /path/to/mount. Then check to see if you can browse img file correctly. – Milan Todorovic Dec 11 '12 at 15:17
@MilanTodorovic: I tried sudo mount -o sdimage.img /dev/mydisk and got: mount: can't find /dev/mydisk in /etc/fstab or /etc/mtab Possibly I need to create some dev entry before. Can you post this as answer with some details? Thanks. – 0123456789 Dec 11 '12 at 15:22
you should not be using dd on mounted devices. unmount all the partitions first, then your command should work. – ubfan1 Dec 11 '12 at 17:33

4 Answers 4

up vote 14 down vote accepted

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

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why is the opposite for me? I've Ubuntu 12.10 and the command has works only with partitions monted... – Velthune Feb 13 '14 at 10:12
@Velthune Are you sure about that? If so, I'd suggest making your own question. – Vreality Jul 17 '14 at 3:58

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

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Both SD are 8 GB. cat can be used to make SD image, but to make another SD I should use dd, right? – 0123456789 Dec 11 '12 at 15:17

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

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Thanks, I will try this. – 0123456789 Dec 11 '12 at 15:17
Doesn't this require two SD card readers? – Peter Mortensen Mar 3 at 20:27

insert the original sd card, check the name of the device (usually mmcblkX or sdcX)

sudo fdisk -l

In my case the sd card is /dev/mmsbkl0. Now you have to unmount the device

sudo umount /dev/mmcblk0

Create image of the device

sudo dd if=/dev/mmcblk0 of=~/sd-card-copy.img

It will take some time ....

Once 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

The write operation is much slower (~X10)

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