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Long story short, I'm working on a Windows 7 machine and I'd like to strip the image off an SD card (backing up the card from a Raspberry Pi). I'm trying to use Cygwin, but not having much success.

Examining the /dev directory, it looks like my SD card is showing up as sdd and sdd1. However, when I run the following command:

dd if=/dev/sdd of=RPi.img

I get the following:

dd: opening '/dev/sdd': Permission denied

I've used dd on a Mac and under Linux without any problem, using similar syntax. What am I missing with Cygwin?

share|improve this question
Have you tried dd if=/dev/sdd1 of RPi.img? – Kruug Apr 10 '13 at 16:30
If I do that, I only get a ~59 MB file from the 4 GB SD Memory Card. Basically I'm only getting the portion of the card that Windows "sees" when you insert the card in the reader. It's not the full image. – GrandAdmiral Apr 10 '13 at 16:35
Could you use a Linux machine, or Linux LiveCD instead of trying in Windows? – Kruug Apr 10 '13 at 16:40
Virtual Linux Machines don't seem to see the SD Memory Card (tried VMware Player and VirtualBox) because I'm using the internal reader on the laptop. Then to top it off.... I don't have a CD burner in the laptop either. :) I have a Mac at home that I can use, I was just trying to find something that would work with my current situation.... and figure out if it was even possible. Seemed like cygwin should have worked. – GrandAdmiral Apr 10 '13 at 16:42
I found that I can also use 'cat /proc/partitions' to get the name of the attached SD Memory Card. – GrandAdmiral May 16 '13 at 15:18
up vote 14 down vote accepted

You get the Permission denied error, because you are not root. That sounds strange in the context of Cygwin, but it hits home.

When you query your status (id) in a normally started Cygwin shell, you'll get something like that:

$ id
uid=1001(user) gid=545(Users) groups=545(Users),555(Remote Desktop Users),513(None)
$ dd if=/dev/sda bs=1000 count=1 | wc -c
dd: opening `/dev/sda': Permission denied

The trick to become root in Cygwin is to start the session elevated, that is, do a right click on your Cygwin icon and choose Run as Administrator. Now your are still not root itself, but at least in root's group:

$ id
uid=1001(user) gid=545(Users) groups=545(Users),0(root),544(Administrators),555(Remote Desktop Users),513(None)

And now, dd works as you are used to it from Un*x:

$ dd if=/dev/sda bs=1000 count=1 | wc -c
1+0 records in
1+0 records out
1000 bytes (1.0 kB) copied, 0.00104424 s, 958 kB/s
share|improve this answer
Very interesting, and that works. Thanks! While both this method and USB Image Tool provide a solution, I'll accept this answer because it's more directly related to my initial question. – GrandAdmiral May 16 '13 at 15:21

Will something like USB Image Tool do?
Or, do you insist on using Cygwin? ...

share|improve this answer
No insistence on using Cygwin. That tool was a little strange when displaying the SD Memory Card (sometimes the info would disappear, but maybe that was Windows doing something) but it seemed to work and it was REALLY FAST. I have a 4 GB file sitting on my computer that is the size I expected. I think I'll diff it with a version from the actual 'dd' command just to make sure. IF that looks good, I'll accept your answer. Thanks! – GrandAdmiral Apr 10 '13 at 16:48
Well, the files didn't match but that could be my fault. I think I booted the RPi after grabbing the first image, not thinking about it. Well, at least I have the backup I wanted now and I have a tool to experiment with down the road that works under Windows. Worst case I'll just drive home and use a sane computer/OS. :) – GrandAdmiral Apr 10 '13 at 18:22

I've had success with dd for Windows, which I believe is a rewrite rather than a port. It's open-source and does not rely on Cygwin.

I particularly liked the dd --list command, which listed all the disk devices along with enough info to identify the one I wanted.

share|improve this answer

I recently had to clone one USB drive to another on windows. My drive is a multiboot with additional software so I didn't want to just copy all files on the FS. DD was a clear choice, but I wasn't on linux so there were a few things I had to do to get it working.

I had cygwin installed and did the following.

first I had to figure out what /dev/sdX device my f: volume was. To do so run this command in cygwin. (TIP: Make sure you start cygwin with admin privs.. *Right click on cygwin and "Run as Administrator")

    cat /proc/partitions
which should output:
   8 0 3813383838 sda
   8 1       4031 sda3 C:\
   8 15  30588303 sdb 
   8 15  30588303 sdb1 E:\
   8 21  30530020 sdc
   8 22  30530020 sdc1 F:\

etc... Here you can clearly see for me to clone my F: drive to my E: drive I'd issue the following command.

dd if=/dev/sdc of=/dev/sdb bs=8M

My image was 32gb.. and I didn't want to just sit and wait with a blinking cursor.. I wanted to see progress so I installed "pv" in cygwin.

dd if=/dev/sdc | pv | dd of=/dev/sdb bs=8M

Now if you want to copy the thumbdrive to an image do the following.

dd if=/dev/sdX | pv | dd of=/cygdrive/c/Users/Myname/Desktop/mythumbdrive.img bs=8M

Hope this helps

share|improve this answer

HDD Raw Copy Tool can make copies of an SD card. If you select "Raw image (dd image)" in the save dialog then it will be identical to the ones made with dd. You can restore images too.

I know it's not done via cygwin, but I personally wouldn't trust it with accessing raw devices.

share|improve this answer
Where do you get the option to save a Raw Image? I saw where you could select the source (SD Memory Card) and the destination (HDD), but then there was just a Start button. Since it wasn't clear what was going to happen next, I exited the program. – GrandAdmiral Apr 10 '13 at 16:56
First you double-click your drive, then on the next screen you double click the "File" option where you can choose where to save the image. – asdasd Apr 11 '13 at 7:49

I see that is now recommending Win32 Disk Imager for writing images to SD Memory Cards. It will also read images from the card, so I'm trying it out now.

share|improve this answer
I refuse to touch that one as there are reports of it trashing your system disc. Rare, but it depends on the hardware and I'm not going to risk it. – tjmoore Aug 13 '14 at 11:58

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