On Fri, Feb 22, 2008 at 09:28:35AM +0100, Oliver Fromme wrote: > 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.
There is also kern.msgbuf_clear. However, this is a sysctl, which means if set to 1 in /etc/sysctl.conf, you'd lose your dmesg output after the OS had started. Bummer. It would be useful if there was a loader.conf variable which was the equivalent of msgbuf_clear. In fact, I'm wondering why the message buffer isn't cleared on shutdown/immediately prior to reboot... Interesting tidbit: We have one production machine which when booted into single-user via serial console for a world install, retains all of the output from that single-user session even once rebooted and brought back into multi-user mode. This poses a substantial security risk, especially during the mergemaster phase (we can discuss why if anyone is curious). -- | Jeremy Chadwick jdc at parodius.com | | Parodius Networking http://www.parodius.com/ | | UNIX Systems Administrator Mountain View, CA, USA | | Making life hard for others since 1977. PGP: 4BD6C0CB | _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
