From: Matt Mackall <mpm@selenic.com>
To: Jon <jg@jguk.org>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
linux-kernel@vger.kernel.org
Subject: Re: dd if=/dev/random of=data.bin bs=512 count=1
Date: Sat, 23 May 2009 14:38:07 -0500 [thread overview]
Message-ID: <1243107487.12761.17.camel@calx> (raw)
In-Reply-To: <4A184ABB.1070902@jguk.org>
On Sat, 2009-05-23 at 20:12 +0100, Jon wrote:
> Hello KOSAKI,
>
> Thank you for your reply.
>
> KOSAKI Motohiro wrote:
> >> Hello
> >>
> >> 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 does not seem very useful to
> have it able to block for so long.
Yes. The theory is that it will be secure even in the event of a
catastrophic failure of the cryptographic compression function. But
don't worry about that; use /dev/urandom.
--
http://selenic.com : development and support for Mercurial and Linux
next prev parent reply other threads:[~2009-05-23 19:39 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-05-17 15:22 dd if=/dev/random of=data.bin bs=512 count=1 Jon Grant
2009-05-17 16:01 ` KOSAKI Motohiro
2009-05-23 19:12 ` Jon
2009-05-23 19:20 ` Samuel Thibault
2009-05-23 19:38 ` Matt Mackall [this message]
2009-05-24 0:59 ` Bill Davidsen
2009-05-17 16:27 ` Bernd Eckenfels
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