The Cult of DD

#1

Post by eklitzke » Fri, Mar 17, 2017, 6:38 PM UTC

Re: The Cult of DD

#2

Post by nwah1 » Fri, Mar 17, 2017, 10:15 PM UTC

Someone should write a wiki bot to crawl through the wikis for Arch, Debian, and so forth to help rewrite all these bad instructions.

Re: The Cult of DD

#3

Post by jsd1982 » Fri, Mar 17, 2017, 10:15 PM UTC

Interesting assertion. Can you show me a shell invocation without using dd that cuts off the first 16 bytes of a binary file, for example? This is a common reason I use dd.

Re: The Cult of DD

#4

Post by 0xdeadbeefbabe » Fri, Mar 17, 2017, 10:19 PM UTC

nwah1 wrote: post #2

Someone should write a wiki bot to crawl through the wikis for Arch, Debian, and so forth to help rewrite all these bad instructions.

In light of this article anything seems possible, so put a pleaserobots.txt in / google bot will modify all the wikis for you.

Re: The Cult of DD

#5

Post by advisedwang » Fri, Mar 17, 2017, 10:22 PM UTC

jsd1982 wrote: post #3

Interesting assertion. Can you show me a shell invocation without using dd that cuts off the first 16 bytes of a binary file, for example? This is a common reason I use dd.

tail -c +17

Re: The Cult of DD

#6

Post by Jtsummers » Fri, Mar 17, 2017, 10:26 PM UTC

advisedwang wrote: post #5

jsd1982 wrote: post #3

Interesting assertion. Can you show me a shell invocation without using dd that cuts off the first 16 bytes of a binary file, for example? This is a common reason I use dd.

tail -c +17

To expand, `-c` tells tail to start on the nth (starts counting at 1) byte. So +1 starts at the beginning, +17 starts after the first 16 bytes. `-n` is lines, `b` is 512-byte blocks.

Re: The Cult of DD

#7

Post by knz42 » Fri, Mar 17, 2017, 10:26 PM UTC

What about the `seek` argument which skips over some blocks at the beginning but still allocates them (unix "holes")?

Also note that there are still unix systems out there which do not support byte-level granularity of access to block devices. On those devices you must actually use a buffer of exactly the size of the blocks on the device. Heck, linux was like this until at least v2.

Re: The Cult of DD

#8

Post by ori_b » Fri, Mar 17, 2017, 10:29 PM UTC

To be fair, dd was mostly a toungue in cheek reference to the overly baroque JCL command for IBM mainframes.

Re: The Cult of DD

#9

Post by noir_lord » Fri, Mar 17, 2017, 10:34 PM UTC

not sure status=progress is that obscure a command, it was added relatively recently as well (in terms of dd).

Re: The Cult of DD

#10

Post by colemannugent » Fri, Mar 17, 2017, 10:35 PM UTC

One thing I'll often use dd for is recovering data from a failing drive. Can head ignore read errors? dd can.

As far as I'm concerned, dd is lower-level than most of the other utilities and provides more control over what's happening.

The author does have a point that the syntax is strange though.