[CentOS-virt] Time

Thu Jan 3 00:27:28 UTC 2013
James B. Byrne <byrnejb at harte-lyne.ca>

On Wed, January 2, 2013 12:51, SilverTip257 wrote:
> On Wed, Jan 2, 2013 at 9:41 AM, James B. Byrne
> <byrnejb at harte-lyne.ca>wrote:
>> I ran into this situation several times whilst testing KVM and the
>> lessons I learned from the experiences can be summarized as:
>> 1.  Never allow the kvm hypervisior to handle guests during a host
>> shutdown.  Use 'virsh shutdown' on each of the guests first and then
>> shutdown the host.  Use autostart to restart guests on a host's
>> reboot.  Write a script to process 'virsh list' to feed active
>> domains
>> to 'virsh shutdown' if automation is required and link that to
>> /etc/rc0.d/K10<whatever>.
> @James:  Can you specifically cite why you manually power down each
> node? Have you tried tweaking your libvirt settings in the config
> file I noted in my earlier response to Robert?

Two reasons.  First, I am minimally familiar with kvm. The niceties of
the options for it is beyond my kin for the nonce.  Second, libvirt
does not always work.  I have had guests refuse to either suspend or
shutdown from an automatic request to do so.  When shutdown is done
manually one discovers right away that there is a problem and which
guest is causing it.

> Set up a central NTP server and have your hosts (and not just VMs)
> connect to it.  It could be the VM host, but doesn't need to be.
> Distribute the load to your NTP server and off of the public NTP pool
> by running an NTP server for your servers to poll [0] ... it's a good
> practice and everybody is happy.

I do that as well.  However, I run one on each host just to serve its
own guests and configure the host to run off our central ntp server.

>> 4.  On each guest have a cron job that checks for ntpd at regular
>> intervals which reports failures and restarts the time service as
>> necessary. We use:
>>   JOBNAME="Check ntpd status and restart if required" ; \
>>     ntpstat > /dev/null && \
>>     if [[ $? -gt 0 ]]; then /sbin/service ntpd start; fi
> Why not configure the ntpd daemon and stick with that?
> It does update on its own [1]. And ntpstat prints out the interval,
> which matches the one mentioned at [1].
> I don't believe the ntpstat script/job is necessary (I've never had to
> do more than set ntpd to run after configuring the servers it should
> poll).

You misunderstand the purpose of the job.  Netstat checks to see if
the daemon is actually running.  If it is not then netstat returns a
non-zero exit code. If the ntpstat exit code is not zero then the
service script is invoked to restart it.  Additionally, netstat writes
out to stderr that it could not find the daemon which gets emailed to
support. I probably should have used [[ ! $? -eq 0 ]] but what I have
written does work.

We found ntpd just stoped on some guests upon occasion without any
visible trace of a cause.  Not frequently but when it did happen it
was a nuisance to detect before clock drift on the guest caused some
failure or other.  This job detects these occurrences and self

These are all CentOS-6.3 hosts and guests.

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