Drivers in linux kernel when media is inserted create /dev entries for supported media organizations such as with sd creating /dev/sda1, etc. as well as the media dev entry /dev/sda.
With images, the loop mount has no support to break up the image into partitions, and require using the loop mount capability to find a supported file system by using offsets into the image.
These offsets are in byte counts, so knowledge of the blocksize of the original media is needed to calculate these offsets.
Also it was noted that some file systems don't support protections in the way linux does with access control in the file system, but just on the overall media. Microsoft fat is the main culprit in that regard. An option can be used to set the mounted media point properly for read access only or read/write.
https://askubuntu.com/questions/445979/how-to-mount-sd-card-image-created-with-dd
Mount with offset to partition
To avoid the need to create separate images for each partition or installing a utility like
kpartx, you can mount each partition individually by specifying an
offset in the
mount command.
First examine the partitions in the image file and determine the offset by using
fdisk:
$ fdisk -u -l rpi_image280914
Disk rpi_image280914: 16.0 GB, 16012804096 bytes
255 heads, 63 sectors/track, 1946 cylinders, total 31275008 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
Disk identifier: 0x000cdac7
Device Boot Start End Blocks Id System
rpi_image280914p1 * 2048 514047 256000 c W95 FAT32 (LBA)
rpi_image280914p2 540672 31242239 15350784 83 Linux
Take the
Start sector of the partition you want and multiply that value by the
Units size. So if you want the second partition you'll get
540672 * 512 = 276824064.
Now create a folder and mount the partition:
mkdir rpi_partition2
sudo mount -o loop,offset=276824064 rpi_image280914 rpi_partition2/
Once you are done doing what you want with the partition data:
sudo umount rpi_partition2/
rm -r rpi_partition2/
2. Windows doesn't support UNIX-style permissions, and you can only
apply permissions to the entire filesystem, not to individual Windows
files/folders. This is done with the "umask" option of the mount
command. In /etc/fstab, change the mount entry for your Windows
partition to this:
/dev/hda6 /mnt/fat vfat users,defaults,umask=000 0 0
(the "users" option allows anyone to mount/unmount the drive and
overrides the default , which is that only root is allowed to
mount/unmount.)
- When issuing the mount command manually, the syntax is:
mount -t vfat -o umask=000 /dev/hda6 /mnt/fat
The value of the permission bits used with umask are the opposite of
those used with the chmod command. For example, the following pairs are
equivalent:
umask=000 and chmod 777
umask=022 and chmod 755
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