Re: [Xen-users] Kernel panic recoverable by hitting <enter>?

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> But, suddenly, a Dell PowerEdge 1750 equipped with SMP Xeon@xxxxxxx and
> 4GB DDR ECC RAM (from crucial.com) running under xen-2.0.5 with
> 2.6.10-xen0 on Debian Sarge and carrying 22 domUs [Sarge|FC4|*BSD] under
> medium load disappeared this afternoon from the network - both the dom0
> and all domUs.

Nice setup!

> The remote-hands service claimed that there was a kernel panic on the
> system's console showing loads of hexdumps and something related to
> 'memory stack' - unfotunately, the guy couldn't remember exactly what
> was shown on the screen [and, sadly, I've no serial console attached to
> that machine and no terminal server, of course ;-)].

Shame they didn't just take a digicam photo and mail it to you.

> Now the odd part, at least for me as I never heard of such a thing: the
> technician also claimed that, after pressing the enter key, the system
> returned to 'normal operation' and showed a conosle login.
>
> When the machine reappeared back on the net it looked like as if nothing
> had happened: Uptime of dom0 is still >90 days, neither the logs of dom0
> nor those of the domUs show any suspicious entries - except some of the
> domU's services complaining about the lack of network connectivity
> (openvpn, etc...).

But all the domUs will still up?

> Do you guys have heard of user-confirmable kernel panics? (I just
> grepped through the xen- and linux-sources but found nothing; Google
> wasn't of much help, either.)

They don't exist...  But that assumes it was a panic.  The message he saw 
could have been some sort of non-fatal oops - have a look in dom0's dmesg 
output.  I guess it might have somehow recovered from <whatever it was> and 
thus returned your connectivity.  Don't ask me what it could be though ;-)

> Was the remote-hands-guy telling me fary tales merely to draw off
> attention from some colo-internal network problems? Or could that be a
> xen-specific experience? How to track that down?

As well as checking the dmesg in dom0, you might also like to check for 
suspicious warnings in xm dmesg - just in case Xen spotted a domain doing 
something weird and complained about it.

Other than that, it seems a bit mysterious...

Cheers,
Mark

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