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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? –  Alex Farber 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. –  Alex Farber 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

3 Answers 3

up vote 10 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? –  Alex Farber 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. –  Alex Farber Dec 11 '12 at 15:17
Doesn't this require two SD card readers? –  Peter Mortensen Mar 3 at 20:27

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