Re: [BLUG] power off CD?

On Mon, Dec 21, 2009 at 08:19:44AM -0500, David Ernst wrote:
> On Sun, Dec 20, 2009 at 11:27:21PM -0500, Steven Black wrote:
> >On Fri, Dec 18, 2009 at 01:11:29AM -0500, David Ernst wrote:
> >> So, we put the CD into the CD drive of my Ubuntu (Jaunty)
> >> machine... it spins up, and ... my computer turns off. power off. As
> >> if our power had gone out, but it hadn't.
> >
> >You should check the kernel logs. (/var/log/dmesg.*)
>
> I thought the dmesg logs wrote only boot-up info..? I took a look and
> didn't see anything, any clues on what you think I should be looking
> for?

After boot up the kernel writes logs to a pipe and either syslog-ng
or klogd will read from the pipe and write to a file. It should cover
issues that crop up after boot.

This log gets rotated at boot, so an 'ls -al dmesg*' will show you the
dates and times of the last write to each log. That can be used to find
the correct file, then look at the last line or so.

I don't know about your distribution, but my distro time-stamps each line
with time-since-boot information (in seconds?). This allows you to look
for the jump from boot time to post-boot messages.

However, if it was the CMOS/BIOS causing the shutdown (as I have seen
before) it is unlikely there will be any meaningful entries in the log.

> >Powering off is unusual. Now, kernel halting due to some hardware issue,
> >that's a lot more common.
>
> Agreed. But would the computer really turn off its power on a kernel
> panic?

Not normally, no.

I believe there is logic in place to prevent kernel dead-locks which
may reboot the system -- I thought it performed a reboot and didn't
shut it down, though.

Such an incident would be flagged in the kernel log.

> >I've seen low-level errors power off machines before. If you have logs
> >available in your CMOS/BIOS settings that may shine some light on it.
>
> next time I reboot, I'll try to take a look. :) I don't remember
> ever seeing such a thing, though.

These logs are fairly common for server hardware, but rare for
desktop/laptop hardware. Look for anything with "Log" in the name. Just
a forewarning, sometimes these are not directly human-readiable and just
contain time-stamps and hex numbers.

Cheers,
Steven Black

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