Partial microSD Image
Instructions to partially clone the image from a microSD (or anything else), where the filesystem does not cover the entire disk. For example, a 128GB microSD with a fresh RasPi image that only encompasses ~5.4 GB of space.
Run sudo fdisk -l to display partitioning details:
Disk /dev/mmcblk0: 119.38 GiB, 128177930240 bytes, 250347520 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: 0x1aa4489a
Device Boot Start End Sectors Size Id Type
/dev/mmcblk0p1 8192 1056767 1048576 512M c W95 FAT32 (LBA)
/dev/mmcblk0p2 1056768 10600447 9543680 4.6G 83 Linux
In this case, sector size of 512 bytes multiplied by the End sector is the total space used by these partitions.
So divide that total size by whatever block size is preferred to use with dd, and round up to an integer:
(10600447 * 512 bytes)/4MB < 1400
Finally, run dd with count:
sudo dd if=/dev/mmcblk0 of=partial_image.img bs=4M status=progress count=1400Check the image with gparted:
sudo gparted partial_image.imgOr, mount the partitions in the image using this technique:
$ sudo mount -o loop,offset=4194304,sizelimit=536870912 ./partial_image.img /mnt/mount_point/bootfs
# offset: 512 bytes * 8192 sectors = 4194304 bytes
# sizelimit: 512 bytes * 1048576 sectors = 536870912 bytes
$ sudo mount -o loop,offset=541065216,sizelimit=4886364160 ./partial_image.img /mnt/mount_point/rootfs
# offset: 512 bytes * 1056768 sectors = 541065216 bytes
# sizelimit: 512 bytes * 9543680 sectors = 4886364160 bytesIf it's just a single partition image, then you can get away with simply this:
sudo mount -o loop partial_image.img /mnt/mount_point/