cool feature of dmesg.boot file

[Bernd Walter]

On Thu, Feb 21, 2008 at 10:29:40PM +0100, Bartosz Giza wrote:
> Hi,
> 
> I have found quite interesting feature on one of router that lately i have 
> taken to administer.
> What i knew was that file /var/run/dmesg.boot holds data from kernel buffer 
> that is taken right after file system(s) are mounted.
> Lately i have found that one router writes to this file data from kernel 
> buffer when system is going to reeboot. Below are few lines from this file.
> What you can see are lines from kernel right before reeboot. I have never seen 
> before such lines in this file. And this is quite interesting. Could anyone 
> tell me how can i achieve such funcionality on other systems ? I have tried 
> to find on google about this but i couldn't find anything similar to this.

You can even see the panic message if it was the reason for reboot.
This works on every system where the RAM is not cleared on reboot.
For example on every alpha, on my old IBM notebook, on Soekris systems,
on at least some Intel server boards, ...
Just not on vanilla PC, because their BIOS clears the RAM contents, so
the old dmesg buffer is lost on the next kernel start.
x86 that don't clear the RAM exists, just as my notebook and Soekris,
but those are not very common.
It is nothing which is configuriable though.
Of course you could ask your board vendor to send you a less destructive
BIOS, but I don't expect any positive result from that.
I guess the main reason for this is that most are using the same BIOS
framework and don't think about it.


> ------
> Waiting (max 60 seconds) for system process `vnlru' to stop...done
> Waiting (max 60 seconds) for system process `bufdaemon' to stop...done
> Waiting (max 60 seconds) for system process `syncer' to stop...
> Syncing disks, vnodes remaining...2 2 2 0 0 done
> All buffers synced.
> GEOM_MIRROR: Device gm0: provider mirror/gm0 destroyed.
> GEOM_MIRROR: Device gm0 destroyed.
> Uptime: 71d13h58m11s
> Copyright (c) 1992-2007 The FreeBSD Project.
> Copyright (c) 1979, 1980, 1983, 1986, 1988, 1989, 1991, 1992, 1993, 1994
>         The Regents of the University of California. All rights reserved.
> FreeBSD is a registered trademark of The FreeBSD Foundation.
> FreeBSD 6.2-RELEASE #0: Sun Feb 18 20:05:19 CET 2007			
> ------
> 
> -- 
> Pozdrawiam
> Bartosz Giza
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-- 
B.Walter                http://www.bwct.de      http://www.fizon.de
bernd at bwct.de           info at bwct.de            support at fizon.de