linux-kernel - Re: dd if=/dev/random of=data.bin bs=512 count=1

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Message-ID: <20090523192008.GD10166@const.famille.thibault.fr>
Date:	Sat, 23 May 2009 21:20:08 +0200
From:	Samuel Thibault <samuel.thibault@...-lyon.org>
To:	Jon <jg@...k.org>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org
Subject: Re: dd if=/dev/random of=data.bin bs=512 count=1

Jon, le Sat 23 May 2009 20:12:59 +0100, a écrit :
> KOSAKI Motohiro wrote:
> >>Issuing this command, I expected to get a file 4096 bytes in size.
> >>Could someone let me know if I have missed something..? Or is there a
> >>problem with using /dev/random this way?
> >>
> >>if I have a count=10 it hangs forever (several hours).
> >>
> >>Changing to use /dev/urandom and it generates the file ok.
> >
> >you already have the answer. /dev/random might blocked, /dev/urandom 
> >doesn't.
> 
> Is this a "feature" of /dev/random ?

It is, as opposed to urandom

> ..it does not seem very useful to have it able to block for so long.

The feature is about to wait for random data to be available, not only
pseudo-random data.

Samuel
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