The process of creating, configuring, and backing up a Raspberry Pi goes a little something like this:
unzip /mnt/diskimages/ISOs/Raspberry\ Pi/2016-11-25-raspbian-jessie-lite.zip sudo dcfldd statusinterval=16 bs=4M if=2016-11-25-raspbian-jessie-lite.img of=/dev/sdb ... Micro SD card to Pi, boot, perform various configuration tweaks ... ... card back to PC ... sudo dcfldd statusinterval=16 bs=4M if=/dev/sdb of=Streamer5-2017-01-02.img zip -1 Streamer5-2017-01-02.zip Streamer5-2017-01-02.img rsync -ahuv --progress Streamer5-2017-01-02.zip /mnt/diskimages/ISOs/Raspberry\ Pi/
The ZIP operation crushes an 8 GB image down to 1.6 GB, obviously depending on most of the image being filled with binary zeros or foxes or something trivial like that. You could work around that with fsarchiver, at the cost of handling each partition separately.
You can pipe the incoming image through GZIP when you don’t need the image right away:
sudo dcfldd statusinterval=16 bs=4M if=/dev/sdb | gzip -1c > Streamer5-2017-01-02.gz
There’s an obvious gotcha when you try to write an image to a (slightly) smaller card than the one it came from. Writing a smaller image on a larger card works just fine.
With a raw image in hand, you must know the disk partition offsets within the image to mount them in loopback mode:
fdisk -l Streamer5-2017-01-02.img Disk Streamer5-2017-01-02.img: 7.4 GiB, 7892631552 bytes, 15415296 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: dos Disk identifier: 0xc280d360 Device Boot Start End Sectors Size Id Type Streamer5-2017-01-02.img1 8192 137215 129024 63M c W95 FAT32 (LBA) Streamer5-2017-01-02.img2 137216 15415295 15278080 7.3G 83 Linux
Knowing the offsets, the mounts go like this:
sudo mount -o loop,offset=$(( 8192*512 )) Streamer5-2017-01-02.img /mnt/loop/ ... snippage ... sudo mount -o loop,offset=$(( 137216*512 )) Streamer5-2017-01-02.img /mnt/loop/
Because a Jessie Lite system will fit neatly into a 2 GB SD Card, you can trim the disk image to eliminate most of the unused space:
sudo losetup -f /dev/loop0 sudo losetup /dev/loop0 Streamer5-2017-01-02.img sudo partprobe /dev/loop0 sudo gparted /dev/loop0 ... resize ext4 partition from 7 GB to 1.8 GB sudo losetup -d /dev/loop0 fdisk -l Streamer5-2017-01-02.img Disk Streamer5-2017-01-02.img: 7.4 GiB, 7892631552 bytes, 15415296 sectors Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: dos Disk identifier: 0xc280d360 Device Boot Start End Sectors Size Id Type Streamer5-2017-01-02.img1 8192 137215 129024 63M c W95 FAT32 (LBA) Streamer5-2017-01-02.img2 137216 3833855 3696640 1.8G 83 Linux truncate --size=$(( (3833855+1)*512 )) Streamer5-2017-01-02.img ... or, if you don't care about an exact fit, use ... truncate --size=2G Streamer5-2017-01-02.img
The partition and filesystem will plump up to fill the SD Card during the first boot on the Raspberry Pi.
There exist automagic utilities for all that, but practicing simple stuff helps keep it all fresh…
