Re: setting time in guest with ntpdate results in VM hang

[Dale Swanston <swanston@sedsystems.ca>]

On 8/24/2012 1:43 PM, Marcelo Tosatti wrote:
> On Fri, Aug 24, 2012 at 09:57:35AM -0600, Dale Swanston wrote:
>> Hello.
>>
>> We are running a guest OS of CentOS 4.4 (kernel 2.6.12) for legacy
>> reasons, upgrading is not an option.   NTP is running on the host
>> and synching with a local GPS NTP server.  But due to frequency
>> drift in the guest it restarts itself periodically and upon start up
>> performs an ntpdate to force a time jump on the guest.
>>
>> I have seen 2 occasions now (over 2 months) where the VM hangs right
>> as the ntpdate command alters the guest clock (based on output in
>> /var/log/messages).
>>
>>  From the host's perspective the VM is still running but it appears
>> to be using very high CPU percentage (more than typical).  The only
>> recovery option is to force shutdown of the VM and restart it.
> This should not happen.
>
>> 1.  Are there any known issues with ntpdate and VMs hanging?  Any
>> workarounds?
>> 2.  Are there any debugging tools further characterise the problem?
> Upgrading the guest kernel is not an option? At least install recent
> kernel in guest to confirm that its not an already fixed bug.

Good idea.  I'll try that.

But are there any tools available to determine what the VM is doing when 
it appears hung?  I've looked but haven't found much on debug or 
diagnostics on a running VM.  Any links?

Is it possible the guest kernel is panicking? What would the VM do if 
that happened?  Would it shutdown?

Thanks again.