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

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On Saturday February 20 2016 13:04, in
comp.os.linux.misc, "pureheart@pacbell.net" <pureheart@pacbell.net> wrote:

> This is probably considered basic stuff but I'm still having trouble
> understanding dd.
> 
> In particular, why do the things it writes/reads to have to be *un*mounted?

They don't.

> How does the system even know that the device exists if it's not mounted?

Quick answer: physical devices are manipulated by device drivers; if a driver
doesn't exist, then the system can't use the device. Device drivers "expose"
themselves as special files (typically, those things you see under the /dev
directory tree). All mount(8)/mount(2) does is connect those special files
that represent device drivers (and thus, devices) to directories in your
filesystem.

> What happens if you *do* write to a mounted device.

If you write to the /dev/* device, you wipe out any filesystem constructs on
that device (but, this is no different than if you write to an /unmounted/
device).

If you try to write to the mountpoint, the system stops you (you can't write
over a directory this way).

If you try to write to a file on the mountpoint, you write to a file on the
mountpoint.

> So far I've read about six dd how-tos, but I have not had the mounting
> explained to my feeble mind's satisfaction.

You aren't as much confused about dd(1) as you are about devices, mounts and
mountpoints. Try looking for information on those instead.

> Anyone have a good url or simple explanation?
> 
> Pureheart in Aptos


-- 
Lew Pitcher
"In Skills, We Trust"
PGP public key available upon request

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Thread

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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