This is a copy past from another person you can find the original blog here:
I am making a copy here is I can find it easy and in case the original disappear of the web.
On Linux you can use
dd to make a backup from SD card. Reverse
of (i.e. to where they point – source and destination) afterwards to restore, but be careful not to restore to a wrong disk. It will be destroyed without a warning!!!
fdisk to get the device id of you SD card (check the size)
then use dd to make a diskimage (change /dev/sdb with what you found with fdisk -l):
dd bs=4M if=/dev/sdb of=image1-`date +%d%m%y`.img
or this to make a compressed image:
dd bs=4M if=/dev/sdb | gzip > image1-`date +%d%m%y`.img.gz
The process will take some time. After the image is created you will notice that it’s too big(size of a SD card). To shrink it we will use a perfect script that I found on github here https://github.com/Drewsif/PiShrink.git called PiShrink.
PiShrink is a bash script that automatically shrink a pi image that will then resize to the max size of the SD card on boot. This will make putting the image back onto the SD card faster and the shrunk images will compress better.
wget https://raw.githubusercontent.com/Drewsif/PiShrink/master/pishrink.sh chmod +x pishrink.sh sudo mv pishrink.sh /usr/local/bin
$ sudo pishrink.sh pi.img e2fsck 1.42.9 (28-Dec-2013) Pass 1: Checking inodes, blocks, and sizes Pass 2: Checking directory structure Pass 3: Checking directory connectivity Pass 4: Checking reference counts Pass 5: Checking group summary information /dev/loop1: 88262/1929536 files (0.2% non-contiguous), 842728/7717632 blocks resize2fs 1.42.9 (28-Dec-2013) resize2fs 1.42.9 (28-Dec-2013) Resizing the filesystem on /dev/loop1 to 773603 (4k) blocks. Begin pass 2 (max = 100387) Relocating blocks XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX Begin pass 3 (max = 236) Scanning inode table XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX Begin pass 4 (max = 7348) Updating inode references XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX The filesystem on /dev/loop1 is now 773603 blocks long. Shrunk pi.img from 30G to 3.1G