Jeremy Chadwick wrote: > Oliver Fromme wrote: > > 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...
So you can see panic messages and other useful things that happened before the reboot. It's a _feature_, not a bug. > 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). sysctl security.bsd.unprivileged_read_msgbuf=0 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.' _______________________________________________ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[EMAIL PROTECTED]"
