This is a discussion on Re: cool feature of dmesg.boot file - FreeBSD ; 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 ...
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.
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