Date: Fri, 22 Feb 2008 09:28:35 +0100 (CET) From: Oliver Fromme <olli@lurza.secnetix.de> To: freebsd-hackers@FreeBSD.ORG, gizmen@blurp.pl Subject: Re: cool feature of dmesg.boot file Message-ID: <200802220828.m1M8SZkj097645@lurza.secnetix.de> In-Reply-To: <200802212229.40988.gizmen@blurp.pl>
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Bartosz Giza wrote: > 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. Upon a reboot, the kernel is usually loaded to the same physical addresses in RAM where it was before, so the dmesg buffer will be at the same location, too (unless you built a new kernel, of course). So all the contents from before reboot are still there -- *IF* the system BIOS didn't clear the RAM. Then the old contents will end up in /var/run/dmesg.boot, too. You could try looking at your BIOS setup. Some have an option called "Quick POST" or similar. If you enable it, the BIOS will skip the RAM test (which is rather useless anyway) which clears the RAM. It might help, but it depends very much on your mainboard and BIOS. Best regards Oliver -- Oliver Fromme, secnetix GmbH & Co. KG, Marktplatz 29, 85567 Grafing b. M. Handelsregister: Registergericht Muenchen, HRA 74606, Geschäftsfuehrung: secnetix Verwaltungsgesellsch. mbH, Handelsregister: Registergericht Mün- chen, HRB 125758, Geschäftsführer: Maik Bachmann, Olaf Erb, Ralf Gebhart FreeBSD-Dienstleistungen, -Produkte und mehr: http://www.secnetix.de/bsd 'Instead of asking why a piece of software is using "1970s technology," start asking why software is ignoring 30 years of accumulated wisdom.'
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