$ sudo dd if=/dev/mmcblk0 of=/path/to/image/file.img bs=4M

/dev/mmcblk0 argument depends on your system. In some system this argument could be /dev/sdX where X is the “device number” that points to the SD card. What is X could be known from:

$ sudo fdisk -l

Make sure you point dd to the device (e.g. /dev/mmcblk0, /dev/sdd), not the partition (e.g. /dev/mmcblk0p1, /dev/sdd1).

Making an image of 8GB SD card will take a long time, and dd won’t give any progress update whatsoever. It’s done, when it says it’s done (Walter White, Breaking Bad. LOL). It took 10 minutes (14.3MB/s) with my laptop. The only way to know the progress is by opening other terminal and check what is the size of the image file. The final size of the image file is same as the size of your SD card. OR you can use one front-end (?) of dd, namely dcfldd.

Before unplugging the SD card don’t forget to flush the buffer/cache:

$ sudo sync

Calculate the SHA1Sum of the image for future purposes. For huge file like this there’s a chance that it will get damaged when you do a lot of moving and transfer.

$ sha1sum file.img >> file.img.sha1sum

This will save the sha1sum into a file named file.img.sha1sum. After this you can compress it, transfer it, anything. Then, before restoring this image back into SD card, calculate the SHA1 once again and compare it to the original SHA1.

To compress the image use this:

$ cd /path/to/image
$ gzip file.img

This will “throw” the empty bits of the image and squeeze the file only with bits that actually contains data.

Restoring The Image

To restore the image first decompress the file

$ gunzip file.img.gz

then use dd

$ sudo dd if=/path/to/image/file.img of=/dev/mmcblk0 bs=4M

don’t forget to flush the cache by

$ sudo sync

TODO:
– sha1sum checking