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SubjectRe: 2.6.9-rc2-mm4
On Tuesday 28 September 2004 07:05, Ingo Molnar wrote:
>* Gene Heskett <> wrote:
>> That would I assume need a null modem cable, and what do I run on
>> the firewall? Minicom? Or is there something better that can
>> just grab and log without being interactive? Its a rh7.3 box with
>> a 2.4.18 era kernel. I'd update that, but its not broken. :)
>here's a mini-howto:
Printed for future reference, thanks

>to set up serial logging:
>install a null modem cable to one of the serial ports of the server,
>connect the cable to another box, run a terminal program on that
> other box (e.g. "minicom -m" - do Alt-L to switch on logging after
> starting it up) and set up the server's kernel to do serial
> logging: enable CONFIG_SERIAL_8250_CONSOLE and
> CONFIG_SERIAL_CORE_CONSOLE, recompile & reinstall the kernel, add
> "console=ttyS0,38400 console=tty0" to your /etc/grub.conf or
> /etc/lilo.conf kernel boot line, reboot the server with the new
> kernel command line - and configure minicom to run with that speed
> (Alt-S).
>e.g. my /etc/grub.conf has:
>title test-2.6 (test-2.6)
> root (hd0,0)
> kernel /boot/bzImage root=/dev/sda1 console=ttyS0,38400
> console=tty0 nmi_watchdog=1 kernel_preempt=1
>if everything is set up correctly then you should see kernel
> messages showing up in the minicom session when you boot up.
>When the messages do not show up then typical errors are mismatch
>between the serial port (or speed) and the device names used - if
> it's COM2 then use ttyS1, and dont forget to set up the serial
> speed option of minicom, etc. You can test the serial connection by
> doing:
> echo x > /dev/ttyS0
>and that should show up in the minicom session on the other box.
>to set up the NMI watchdog:
>add nmi_watchdog=1 to your boot parameters and reboot - that should
> be all to get it active. If all CPU's NMI count increases in
>/proc/interrupts then it's working fine. If the counts do not
> increase (or only one CPU increases it) then try nmi_watchdog=2 -
> this is another type of NMI that might work better. (Very rarely
> there are boxes that dont have reliable NMI counts with 1 and 2
> either - but i dont think your box is one of those.)
>once the NMI watchdog is up and running it should catch all hard
> lockups and print backtraces to the serial console - even if you
> are within X while the lockup happens. You can test hard lockups by
> running the attached 'lockupcli' userspace code as root - it turns
> off interrupts and goes into an infinite loop => instant lockup.
> The NMI watchdog should notice this condition after a couple of
> seconds and should abort the task, printing a kernel trace as well.
> Your box should be back in working order after that point.
>now for the real lockup your box wont be 'fixed' by the NMI
> watchdog, it will likely stay locked up, but you should get
> messages on the serial console, giving us an idea where the kernel
> locked up and why. (Very rarely it happens that not even the NMI
> watchdog prints anything for a hard lockup - this is often the sign
> of hardware problems.)
> Ingo
>--- lockupcli.c
>main ()
> iopl(3);
> for (;;) asm("cli");

Cheers, Gene
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
99.26% setiathome rank, not too shabby for a WV hillbilly attorneys please note, additions to this message
by Gene Heskett are:
Copyright 2004 by Maurice Eugene Heskett, all rights reserved.
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