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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.

Tim
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  • last i heard it was a "squashfs". ref: https://en.wikipedia.org/wiki/SquashFS – Theophrastus Apr 23 '17 at 02:11
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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 '17 at 13:05
  • do you mean `ISO9660` is a file system type? @ridgy – Tim Apr 23 '17 at 14:26
  • "ISO 9660 is the standard file system for CD-ROMs" (http://wiki.osdev.org/ISO_9660) – ridgy Apr 23 '17 at 14:51

2 Answers2

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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.

Gilles 'SO- stop being evil'
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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 '17 at 01:46
  • 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 `, in your case `file input.iso`; this looks for the 'real' content of the file. See my older comment. – ridgy Apr 27 '17 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.

linerd
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