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Re: [libvirt] Enhancement: Random Clock Offset

On Fri, Mar 11, 2016 at 10:46:24PM +0000, bancfc openmailbox org wrote:
On 2016-03-02 10:22, Daniel P. Berrange wrote:

Agreed, this feature is really a specific usage policy. Libvirt aims to
focus on providing mechanism, letting specific policies be implemented
by the management applications using libvirt. We already allow the time
offset to be set to an arbitrary number of seconds, so apps starting a
guest can change that value as desired each time. So I don't think
there is anything should do in libvirt for this.


:( I can't really use the guest-agent because its advised against
running it in an untrusted environment. Has this situation changed?

Also the changes we can do on the host side is really limited to just a
VMs configuration XML to keep things simple and self contained.

In that case qemu can still help.  And libvirt has a way to configure
that.  There's just one downside being that if the guest resets the time
itself (e.g. based on ntp or whatever), it will not be reset.

Example configuration:

 <clock offset='variable' adjustment='-12' basis='utc'/>

This should set up the RTC in a way that it starts with the time of UTC
minus 12 seconds.  You can also set up the RTC to be in a specific
timezone, but that's not as finely grained as you'd like, I guess.  More
info on how to set that up in our docs [1].


[1] https://libvirt.org/formatdomain.html#elementsTime

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