[TriLUG] cp of /dev hangs, but not tar

[Robert Dale]

On 6/19/07, Joseph Mack NA3T <jmack at wm7d.net> wrote:
> On Tue, 19 Jun 2007, Michael Tharp wrote:
>
> > No, but there are plenty of finitely-sized device nodes that contain
> > useful data. For example. you could `cp --copy-contents /dev/cdrom
> > foobar.iso`, although for this purpose I usually utilize dd.
>
> OK so cp can do the same job as dd (under the right
> circumstances). Why do you "usually" use dd? Is there some
> other wrinkle?

dd gives you much more control at the byte level.

Things I've found it useful for...

- copying the partition table before making changes
  dd if=/dev/sda of=part.bak bs=512 count=1

- wipe the MBR
  dd if=/dev/zero of=/dev/sda bs=446 count=1

- making empty files, as in preparation for a filesystem or swap file
  dd if=/dev/zero of=encrypted.fs bs=1G count=1

- wiping devices (before fancy data destroyers came along)
  dd if=/dev/urandom of=/dev/sda

- extracting pieces from files, in particular proprietary binary files
  dd if=foo.dat of=data.interesting skip=4 bs=32 count=128

- copying  filesystems

- reading around bad blocks

other tips:
http://www.codecoffee.com/tipsforlinux/articles/036.html

-- 
Robert Dale