linux-kernel - Re: Seeding /dev/random not working

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Message-ID: <20070529202337.GH11166@waste.org>
Date:	Tue, 29 May 2007 15:23:37 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	M Macnair <mmacnair@...il.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org
Subject: Re: Seeding /dev/random not working

On Tue, May 29, 2007 at 05:44:37PM +0100, M Macnair wrote:
> On 29 May 2007 18:58:59 +0200, Andi Kleen <andi@...stfloor.org> wrote:
> >"M Macnair" <mmacnair@...il.com> writes:
> >>
> >> Many distros ship with an init script that saves and restores the
> >> entropy pool on startup and shutdown.  The bit that interests me that
> >> is called on startup is (my comments):
> >>       if [ -f $random_seed ]; then
> >>               cat $random_seed >/dev/urandom  # should seed the pool
> >.OA
> >Writing doesn't actually work; to get real accounted entropy for 
> >/dev/random
> >you need to use a special ioctl. I ran into this problem some years ago
> >and ended up writing http://www.muc.de/~ak/rndfeed.c
> >
> >-Andi
> 
> If this doesn't work, then it seems to me as though all the
> debian-esque distros that use equivalents of the above script are
> wasting their time, and the man page recommending that technique (man
> 4 random) is also wrong.  Is that interpretation correct?

Andi is incorrect. Writing does work and everything you write is mixed
into the pool. It's just not counted as entropy credit. This is as
intended.

-- 
Mathematics is the supreme nostalgia of our time.
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