Re: [PLUG] Multimedia blues

[Rich Freeman <r-plug@thefreemanclan.net>]

On Sat, Jul 8, 2017 at 4:14 PM, Charlie Li <ml+PLUG@vishwin.info> wrote:
>
> Have had this happen to me a few times, all of which have been
> completely random. No logs whatsoever.
>

Are you checking for logs in a manner that would catch entries that
were not written to disk?  If there is a kernel panic/bug/etc there
might not be any IO to disk, and if the console was in graphics mode
you might not see any on-screen output.

If you can ssh into the box while it is otherwise hung that is a clean
way of seeing what is going on that doesn't rely on the graphics
drivers/etc.  Otherwise, your best bets for capturing output would be
a serial console, or outputting via UDP:
https://www.kernel.org/doc/Documentation/networking/netconsole.txt

If the kernel actually panics and you have a crash kernel set up it
might capture a core dump which you could analyze.  If it doesn't
actually panic I suspect this would not be triggered even if your
distro otherwise supports it.

Kernel debugging is a bit different from regular application
debugging.  Features like the network console logging are designed to
be fairly low-level and simple so that they can work even if the
kernel is crippled (it doesn't even rely on ARP).  I've used this to
debug some issues I've had with multimedia/graphics/etc, since the
console is often useless in these situations.

If the distro is set up to capture crash dumps you might get something
useful by forcing a panic while it is stuck (Alt-SysRq-C if enabled).
This command should be no worse than hitting the reset button, but
shouldn't be used on a system you can otherwise get into.

-- 
Rich
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