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I am following this post to create bootable Ubuntu flash drive. https://askubuntu.com/a/377561

Suppose my flash drive is /dev/sdb.

After running

sudo dd bs=4M if=input.iso of=/dev/sdb

does the flash drive have a file system? If yes, what file system type?

Thanks.

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  • last i heard it was a "squashfs". ref: en.wikipedia.org/wiki/SquashFS Apr 23, 2017 at 2:11
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    dd does not create any filesystem by itself, but creates an exact copy of the input. So if your .iso file has e.g. ISO9660, then the flash drive will have the same. You can find out with file input.iso and file /dev/sdb.
    – ridgy
    Apr 23, 2017 at 13:05
  • do you mean ISO9660 is a file system type? @ridgy
    – Tim
    Apr 23, 2017 at 14:26
  • "ISO 9660 is the standard file system for CD-ROMs" (wiki.osdev.org/ISO_9660)
    – ridgy
    Apr 23, 2017 at 14:51

2 Answers 2

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dd just copies the input to the output. dd bs=4M if=input.iso of=/dev/sdb is equivalent to cat input.iso >/dev/sdb (unless dd decides not to copy the whole input). This command doesn't create a filesystem, it copies whatever the file input.iso contains.

If, as the name suggests, input.iso contains an ISO 9660 filesystem (the filesystem of CD-ROMs), then this is what the flash drive will contain. If input.iso contains something else then that something else is what the flash drive will contain.

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  • Thanks. can an iso file contain a file system of any file system type, or contain data without file system at all? How can I find out the file system type contained in an iso file?
    – Tim
    Apr 24, 2017 at 1:46
  • You might rename any file you like to something.iso. In *nix OS the file extension is just a convenience, but does not mean anything really. To find out the content of a file, use file <filename>, in your case file input.iso; this looks for the 'real' content of the file. See my older comment.
    – ridgy
    Apr 27, 2017 at 10:24
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The dd command just copies data from input.iso archive to /dev/sdb. File system is just a convention to organize data on a device/disk, and dd doesn't care about it.

And FYI, an iso archive contains ISO9660 filesystem.

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