How to use dd to backup an SD card

Ian D · 03-09-2014, 11:38 AM

I have a RaspberryPi with its OS on an SD card. Sometimes, the SD card gets corrupted and I have to rebuild from scratch.

I am sure that I can use dd (on a different machine) to make a backup copy (and have seen other posts which confirm this).

My question is, on my 'other' box, when I plug in the SD card, how do I know which entry in /dev is the one I need to back up? (Presumably, when the card is inserted and File Manager asks if I want to mount it and open with File Manager, I say 'No')?

Ian

Sydney · 03-09-2014, 01:52 PM

Code:

sudo fdisk -l

Plug in the card

Code:

sudo fdisk -l

You will see the new entry.

sgosnell · 03-09-2014, 06:13 PM

I prefer blkid to fdisk, but both will give you the information. They give different information in different formats, but both will give you the /dev/ info you need.

For making a backup of a boot disk in its entirety, make sure you use, for example, /dev/sdd, and not /dev/sdd1. You want to copy all the partitions, not just one. Back up to a drive at least as large as the one you are using, of course, and realize that after running dd, the drive you backed up to will now only be the size of the SD card, with any excess unallocated.

Drakeo · 03-10-2014, 03:26 AM

did you try lsusb to find the device then dmesg to see where the kernel placed that device. blkid will give you some good info also.

suicidaleggroll · 03-10-2014, 10:13 AM

Either run fdisk -l before and after plugging in the card, or run "tail -f /var/log/messages" while plugging in the card. It doesn't have to be any more complicated than that.

Quote:

Originally Posted by sgosnell

of course, and realize that after running dd, the drive you backed up to will now only be the size of the SD card, with any excess unallocated.

Only if he copies it to a raw device, which would be rather pointless (unless he's trying to duplicate the SD card rather than back it up). Copy it to a file and it's a non-issue.

rtmistler · 03-12-2014, 07:15 AM

It may still get mounted even though you choose to not open a folder in your file manager. A good idea is to check and umount any drives associated with the SD card before you perform the dd command.

sgosnell · 03-12-2014, 08:42 AM

I was assuming the OP was making another bootable SD card. Perhaps a bad assumption.

schneidz · 03-12-2014, 08:48 AM

Quote:

Originally Posted by Ian D

I have a RaspberryPi with its OS on an SD card. Sometimes, the SD card gets corrupted and I have to rebuild from scratch.

I am sure that I can use dd (on a different machine) to make a backup copy (and have seen other posts which confirm this).

My question is, on my 'other' box, when I plug in the SD card, how do I know which entry in /dev is the one I need to back up? (Presumably, when the card is inserted and File Manager asks if I want to mount it and open with File Manager, I say 'No')?

Ian

df -h worx for me.

this is what i do to duplicate usb's/sd's of the same size (or if the output drive is bigger):

Code:

dd bs=8192 if=/dev/sdx of=/dev/sdy

since this is very destructive i usually do this to have an interim backup:
http://www.linuxquestions.org/questi...3/#post4981710

this will make it compress better:
http://www.linuxquestions.org/questi...7/#post5097181

and one can use gparted to expand the boundery of the new sd-card if it is bigger.