How could I record the information when kernel panic.

How could I record the information when kernel panic.

[disnoir]

There is a random probability that cause the kernel panic (debian with 
kernel 3.2.41), when I execute:
"sudo umount /media/data /media/big".

Things are like this:

I use "udisks --mount /dev/sda3" to mount "data" which is a ntfs filesystem.
similarly, I use "udisks --mount /dev/wd5000bpvt/big" to mount "big" 
which is a ext4 filesystem.

After finish using these filesystems, I use "sudo umount /media/data 
/media/big" to umount the filesystems, and the hole system just suddenly 
halt (mouse is not moving).

using alt-sysrq-b to reboot the system. nothing record in the 
/var/log/messages.

So, How could I record the kernel error/info, when system was halt ?

Thanks a lot!


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Re: How could I record the information when kernel panic.

[Brandon Philips]

On Wed, Apr 24, 2013 at 10:18 AM, disnoir <disnoir@gmail.com> wrote:
> So, How could I record the kernel error/info, when system was halt ?

Your best bet is to use one of the following:
0) Use sysrq to investigate a bit:
https://www.kernel.org/doc/Documentation/sysrq.txt
1) Hook a serial console up if your system has one to another system
with a null modem cable and console=ttyS0,<baud> passed in to the
kernel at boot
2) Try netconsole if you don't have a serial console:
https://www.kernel.org/doc/Documentation/networking/netconsole.txt

I would recommend trying a newer kernel and see if your bug is fixed.
If it is you could bisect down to the commit that fixes it and let the
debian kernel maintainers know.

Good luck,

Brandon
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Re: How could I record the information when kernel panic.

[disnoir]

On 04/27/2013 01:33 AM, Brandon Philips wrote:
> On Wed, Apr 24, 2013 at 10:18 AM, disnoir<disnoir@gmail.com>  wrote:
>> So, How could I record the kernel error/info, when system was halt ?
> Your best bet is to use one of the following:
> 0) Use sysrq to investigate a bit:
> https://www.kernel.org/doc/Documentation/sysrq.txt
> 1) Hook a serial console up if your system has one to another system
> with a null modem cable and console=ttyS0,<baud>  passed in to the
> kernel at boot
> 2) Try netconsole if you don't have a serial console:
> https://www.kernel.org/doc/Documentation/networking/netconsole.txt
>
> I would recommend trying a newer kernel and see if your bug is fixed.
> If it is you could bisect down to the commit that fixes it and let the
> debian kernel maintainers know.
>
> Good luck,
>
> Brandon
Thank you for your reply.
I use ttyUSB0 to record the dmesg, cause this is a notebook 
(asus-k42je), which has no serial port, so I use a 
serial-port-to-USB-convertor.
I found that if I add console=ttyUSB0,115200n8 to kernel parameter, the 
kernel will fail to boot, and also without any information.
so I get into system on normal configuration (without console=...), and 
modify rsyslog.conf to log kernel info to /dev/ttyUSB0.
That works, use another pc to watch that serial port, all the 
information in dmesg will show in that serial port either.
But, when I test that if will also work during the kernel-panic ( I try 
"echo c > /proc/sysrq-trigger" ), nothing record into serial.
I guess kernel crash will cause rsyslogd no working.
So I use kdump-tools, kexec-tools to record a kernel dump, and this 
could work even on kernel-panic.
Now, I just need to wait the problem happen again.

:-)

disnoir
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