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Date:      Thu, 10 May 2001 15:07:13 -0500
From:      Dan Nelson <dnelson@emsphone.com>
To:        Mikko Tyolajarvi <mikko@dynas.se>
Cc:        sudakov@sibptus.tomsk.ru, questions@FreeBSD.ORG
Subject:   Re: dmesg buffer between reboots
Message-ID:  <20010510150713.C18228@dan.emsphone.com>
In-Reply-To: <200105101812.f4AICGv90535@explorer.rsa.com>; from "Mikko Tyolajarvi" on Thu May 10 11:12:16 GMT 2001
References:  <3AFA39FA.6EC0F4EA@DougBarton.net>; <20010510155907.A51971@sibptus.tomsk.ru> <200105101812.f4AICGv90535@explorer.rsa.com>

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In the last episode (May 10), Mikko Tyolajarvi said:
> Hmm... on several of my machines, this already happens.  I haven't
> done anything special.  Thus:
> 
> mikko% dmesg
> [...]
> panic: page fault
> 
> syncing disks... 1 
> done
> Uptime: 13d10h9m50s
> /dev/vmmon: Mkdule vmmon: unloaded
> Automatic reboot in 15 seconds - press a key on the console to abort
> Rebooting...
> Copyright (c) 1992-2000 Tha FreeBSD Project.

It all depends on the motherboard/BIOS.  Some zero out the RAM between
reboots, some don't.  I believe this trick also only works if you
always boot the same kernel (different sized kernels will store the
dmesg buffer in different places in memory).

I seem to remeber idle speculations on somehow stuffing the dmesg
buffer in video RAM somewhere, since it stands a better change of
surviving warm boots (the BIOS doesn't touch it).

-- 
	Dan Nelson
	dnelson@emsphone.com

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