From owner-freebsd-questions@FreeBSD.ORG Mon Feb 7 12:29:03 2005 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id D074E16A4CE for ; Mon, 7 Feb 2005 12:29:03 +0000 (GMT) Received: from dire.bris.ac.uk (dire.bris.ac.uk [137.222.10.60]) by mx1.FreeBSD.org (Postfix) with ESMTP id 60D9343D3F for ; Mon, 7 Feb 2005 12:29:03 +0000 (GMT) (envelope-from Jan.Grant@bristol.ac.uk) Received: from mail.ilrt.bris.ac.uk ([137.222.16.62]) by dire.bris.ac.uk with esmtp (Exim 4.44) id 1Cy7xh-0000Eb-Ce; Mon, 07 Feb 2005 12:26:38 +0000 Received: from cmjg (helo=localhost) by mail.ilrt.bris.ac.uk with local-esmtp (Exim 4.44) id 1Cy7xb-0001ew-To; Mon, 07 Feb 2005 12:25:48 +0000 Date: Mon, 7 Feb 2005 12:25:47 +0000 (GMT) From: Jan Grant X-X-Sender: cmjg@mail.ilrt.bris.ac.uk To: Jay Moore In-Reply-To: <200502061721.27613.jaymo@cromagnon.cullmail.com> Message-ID: References: <200502061721.27613.jaymo@cromagnon.cullmail.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: Jan Grant X-Spam-Score: 0.0 X-Spam-Level: / cc: freebsd-questions@freebsd.org cc: Gert Cuykens Subject: Re: what is /entrophy ? X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 07 Feb 2005 12:29:03 -0000 On Sun, 6 Feb 2005, Jay Moore wrote: > On Wednesday 02 February 2005 05:52 am, Gert Cuykens wrote: > > > what is /entrophy ? can i delete it ? > > I believe it is a mis-spelled version of /entropy Your computer attempts to collect "randomness" by sampling the timings of various physical events. That's what the /dev/random device provides: this kernel-harvested randomness. Various cryptographic systems require a supply of "good" random numbers in order to operate. When the machine first boots, the kernel's entropy pool is empty. It would consequently take potentially quite a few minutes to harvest sufficient randomness from interrupts in order to satisfy the needs of such things as sshd. The solution is the /entropy file: when the machine shuts down, it saves "spare" random bits that have not yet been used into this file. On reboot, the kernel's random pool is reinitialised using these "spare" bits. Assuming nobody's sneaked a peek at them in the itme the machine's been turned off, this is a reasonable way to quickly satisfy the startup requirements for randomness. -- jan grant, ILRT, University of Bristol. http://www.ilrt.bris.ac.uk/ Tel +44(0)117 9287864 or +44 (0)117 9287088 http://ioctl.org/jan/ You see what happens when you have fun with a stranger in the Alps?