I'm long accustomed to mounting ISOs on the loop device as a convenient way of examining and modifying them. I'm now faced with the next step.

I downloaded the latest Raspian image for my Rpi - 1.3GB - then dd'd it to an SD card which booted badly. It contains two partitions, the FAT boot and the EXT4 OS. I'd like to examine the image, maybe even copy out the OS partition whilst leaving the boot partition alone, but this is a step I've not tried before. My first attempts failed - does the system recognize such device names as loop01 and loop02 for the partitions on loop0? Dunno.

Does anyone know how to do this?

partx or losetup - the latter manpage has an example just for you

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run fdisk on the image to find the starting block of the partition you want to mount within the image. Then use mount with -o loop,offset=< your blocksize*startblock >

Make sure you unmount the inner partition before unmounting the outer .iso

This works for me on fedora/centos.

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Thanks to both for solutions. Not as hard as I thought!