GNU bug report logs - #7362
dd strangeness

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Message #14 received at 7362-done <at> debbugs.gnu.org (full text, mbox):

From: Lucia Rotger <lucia <at> aircomp.aero>
To: Pádraig Brady <P <at> draigBrady.com>
Cc: 7362-done <at> debbugs.gnu.org
Subject: Re: bug#7362: dd strangeness
Date: Wed, 10 Nov 2010 18:47:48 +0100

Thanks, I'll try it, but it's not in the info or man pages.

Also, the section under FLAGS is badly formatted with the different 
options all in one line. You might want to fix that.

Lucia

On 10/11/2010 16:29, Pádraig Brady wrote:
> On 10/11/10 10:22, Lucia Rotger wrote:
>> I see this behavior in Solaris, Linux and BSD dd: if I send a big enough
>> file they all read it short at the end of the stream.
>>
>> This works as expected:
>>
>> # cat /dev/zero | dd bs=512 count=293601280 | wc
>>
>> I get the expected results, dd reads exactly 293601280 blocks and wc
>> sees 150323855360 characters, 140 GB
>>
>> Whereas substituting cat for zfs send doesn't:
>>
>> # zfs send<backup>  | dd bs=512 count=293601280 | wc
>
> different write sizes to the pipe mean
> in the later case, dd will get short reads.
> IMHO dd is doing the wrong/most surprising thing here,
> but it can't be changed for compatibility reasons.
> You can get coreutils dd to do what you want with:
>
> dd iflag=fullblock
>
> cheers,
> Pádraig.
>

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