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Re: Is there a good "dd for dummies" tutorial around?

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On 2016-02-25 00:55, pureheart@pacbell.net wrote:

> Hi Carlos.
> Thank you and all the others for the replies.
> I have no task in mind, I just have a hard time understanding how it can do *anything* to unmounted drives....the replies have helped set me straight, Mr. Heller's reply, especially.

Ah.

Well, it is nothing specific to 'dd', but how Linux (or Unix) works.
Everything is a file. You can write to files, as in Windows, but you can
also directly write to the raw disk, without format. For this we write
to the file that represents the disk (say, /dev/sdb2). And in order that
nothing interferes, we umount it.

That is, we can write to the disk directly, or to the formatted
structure that is the same disk when mounted. With files and
directories. Two views of the same thing.


In MSdos, or Windows, in order to write to the disk directly you need
specially written software.

In Linux, you can edit a text file and write it as normal file, or you
can directly write it to the raw disk, without format. Say:

echo "Hello World" > /dev/sdb

Of course, the disk would only contain that. A waste. You could write a
thousand files one after the other, and somehow mark when each one
starts and ends. Using tar, for instance. Tapes were done this way,
actually. Databases can used on a partition without format. Some
database prefer it this way.

The database, or the tar archive, would first store some structure that
allows for locating where each thing we store on the disk is. Up to us
to define everything.

Instead, a mounted disk has an structure that does the same thing, but
for general use. It contains metadata assigning blocks to files, lists
of files, and files. And instead of writing to "/dev/sdb5", we would
write to "/mnt/somewwere" (arbitrary).


What makes 'dd' different is that it has options that make it suitable
to raw device writing. Like writing to a specific spot.

-- 
Cheers,
       Carlos E.R.

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Is there a good "dd for dummies" tutorial around? pureheart@pacbell.net - 2016-02-20 10:04 -0800
  Re: Is there a good "dd for dummies" tutorial around? Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2016-02-20 20:24 +0200
  Re: Is there a good "dd for dummies" tutorial around? William Unruh <unruh@invalid.ca> - 2016-02-20 18:26 +0000
  Re: Is there a good "dd for dummies" tutorial around? Robert Heller <heller@deepsoft.com> - 2016-02-20 12:40 -0600
  Re: Is there a good "dd for dummies" tutorial around? Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2016-02-20 14:10 -0500
  Re: Is there a good "dd for dummies" tutorial around? "Carlos E. R." <robin_listas@invalid.es> - 2016-02-22 02:59 +0100
    Re: Is there a good "dd for dummies" tutorial around? "Carlos E.R." <robin_listas@invalid.es> - 2016-02-22 04:39 +0100
      Re: Is there a good "dd for dummies" tutorial around? pureheart@pacbell.net - 2016-02-24 15:55 -0800
        Re: Is there a good "dd for dummies" tutorial around? "Carlos E. R." <robin_listas@invalid.es> - 2016-02-26 03:39 +0100
          Re: Is there a good "dd for dummies" tutorial around? pureheart@pacbell.net - 2016-02-29 18:05 -0800
            Re: Is there a good "dd for dummies" tutorial around? The Natural Philosopher <tnp@invalid.invalid> - 2016-03-01 02:45 +0000
            Re: Is there a good "dd for dummies" tutorial around? "Carlos E.R." <robin_listas@invalid.es> - 2016-03-01 11:14 +0100

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