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lab 17.2 - a doubt

Hi there,

I have a doubt about the lab 17.2 where we are asked to partition a Disk Image File.

The doubt I have is: how does the fdisk utility recognizes that "imagefile" is (or could be) a disk. Since it is not mounted, the only thing that could indicate to the system that it is in fact a disk, is that it has a file system created on it. I also created another file, out of curiosity, and I didn't create a file system on it, and I can also do the same operations as requested on the lab.

So my question really is, that one could partition any file?
how does the fdisk utility even know what is that it is partitioning?

Comments

  • Hi there, I notice there's not too much interest in answering my question. I would like to elaborate.

    I have been reviewing the labs, and some times I get confused, because in some labs we use fdisk to create partitions and in other lbs we are using mkfs to create partitions. And in other ones we are using parted to create partitions. So, my question really is: are those three commands equivalent, in that they are all used to "format disks" or to "create partitions" and/or "make FS"? fdisk/mkfs/parted?

    The other question is: when we are creating files using dd, using /dev/zero as a source, I can see that the outfile is:
    file imagefile
    imagefile: data
    and even before assigning this file as a loopback device, I can use all 3 utilities in the output file. But, surely, I cannot mount it. I have even tried to run fdisk/parted/mkfs on copies of binary files on my system, and have succeeded. So my question really is: you can use any file as a target for formatting/partitioning/makingFS?

  • coop
    coop Posts: 880

    mkfs formats a disk partition or a file ; it does not create either. Linux utiltiies sense what kind of entity (parition, particular type of file) etc by looking at the object, usually the first few bytes, and don't care about extensions almost ever. You can use any file as a filesystem with mkfs (and you will erase the contents when you do) but you need to mount as a loopback device, not a partition. Once again, you usually don't have to specify -o loop on the mount command as mount is smart and knows when it is a file rather than /dev/.... .

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