Re: [gentoo-amd64] Capturing hard hang info?

[Rich Freeman]

On Sat, Oct 19, 2013 at 6:01 PM, Mark Knecht <markknecht@×××××.com> wrote:
> No magic sys request keys, keyboard and
> mouse are dead, cannot shell in or even ping from another machine on
> the network.

These types of situations are really annoying to debug.  Do you get
anything on the console?  Try leaving at a text console with no screen
saver so that you have a chance to see any panic message/etc that
might be left there.  If you have something set to put your monitor to
sleep then after the panic your system will not wake up.

Serial console is another option, albeit not exactly convenient.

I have on my blog somewhere instructions for setting up kdump, but to
be honest with recent kernel versions it hasn't been working (that
could have changed).  You can configure your kernel to auto-reboot to
a panic kernel which you can then use to dump core to disk, then you
can reboot back into your normal system to examine it at your leisure.
 That should tell you what was going on when it crashed, but only if
the kernel actually detected a panic (usually it does).

Note that logs are useless in a panic (unless you're using kdump) as
the kernel will not write anything to disk following a panic.  If you
get an oops/bug you might or might not get anything in your logs
depending on whether it affected the filesystem/disk/etc subsystems.
If the kernel knows its internals are scrambled the last thing you
want it doing is trying to write to your filesystems.  With kdump it
does a reboot into a new kernel which fully re-initializes everything
and then dumps ram safely to disk.

Rich