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    SubjectRe: 2.6.9-rc2-mm4
    Date
    On Tuesday 28 September 2004 07:05, Ingo Molnar wrote:
    >* Gene Heskett <gene.heskett@verizon.net> 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
    Yahoo.com attorneys please note, additions to this message
    by Gene Heskett are:
    Copyright 2004 by Maurice Eugene Heskett, all rights reserved.
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