Re: Is it true that `dd` is almost not needed?

On Sat, 11 Dec 2021 18:06:43 +0200
<uxer@mailo.com> wrote:

> The Cult of DD
> Mar 17, 2017
> You'll often see instructions for creating and using disk images on Unix
> systems making use of the dd command. This is a strange program of
> [obscure provenance](https://en.wikipedia.org/wiki/Dd_(Unix)) that
> somehow, still manages to survive in the 21st century.
>
> Actually, using dd is almost never necessary, and due to its highly
> nonstandard syntax is usually just an easy way to mess things up. For
> instance, you'll see instructions like this asking you to run commands
> like:
>
> […snip…]
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> End of article and my questions:
>
> Is the author right in general?
> Is the author right for Linux environment?
> Is the author right for OpenBSD environment?

Can `cat`/`tail` et all, create a "sparse" file?
> vk4msl-gap$ dd if=/dev/zero bs=1M count=1 seek=9 of=sparsefile
> 1+0 records in
> 1+0 records out
> 1048576 bytes transferred in 0.009 secs (108639200 bytes/sec)
> vk4msl-gap$ ls -lh sparsefile
> -rw-r--r-- 1 stuartl stuartl 10.0M Dec 12 08:42 sparsefile
> vk4msl-gap$ du -hs sparsefile
> 1.0M sparsefile

Very useful for "thin provisioning" of raw disk images with virtual
machines.

Can `cat`/`tail` et all read bytes from the middle of a file?
> vk4msl-gap$ echo -n '000102030405060708090a0b0c0d0e0f' > test
> vk4msl-gap$ dd if=test of=test.part bs=2 skip=4 count=4
> 4+0 records in
> 4+0 records out
> 8 bytes transferred in 0.000 secs (66541 bytes/sec)
> vk4msl-gap$ cat test.part
> 04050607

Can `cat`/`tail` et all overwrite specific bytes in the middle of a file?
> vk4msl-gap$ echo -n 'aaabacad' | dd of=test bs=2 count=4 seek=8 conv=notrunc
> 4+0 records in
> 4+0 records out
> 8 bytes transferred in 0.000 secs (98985 bytes/sec)
> vk4msl-gap$ cat test
> 0001020304050607aaabacad0c0d0e0f

I think you'll find `dd` was written in the era of magnetic tapes as a
storage medium, and so the ability to seek to a specific part of a tape
then perform a read or write, was seen as a critical feature of the day.

That same feature is handy when doing various low-level disk operations
as well (e.g. backing-up/restoring the boot sector/partition table).
--
Stuart Longland (aka Redhatter, VK4MSL)

I haven't lost my mind...
...it's backed up on a tape somewhere.