Re: [Help-bash] set time

[Bob Proulx]

Greg Wooledge wrote:
> On Fri, Sep 14, 2012 at 04:10:34PM +0000, address@hidden wrote:
> >  I often have wild drifts in my virtual machines, the sort that ntp
> > can't deal with and internet access is quite often not available
> > (thus, no ntpdate either).
> 
> I don't know much about virtual computing.  Can't you at least sync the
> virtual machines to the host OS's clock?

+1.  I believe that is always the correct solution.  Always sync the
virtual machine system clock to the host system clock.  And then
whether networking is available outside of that doesn't matter because
networking would always be available between the virtual machine and
the host system.

> > So I use a script that shifts the time by one second or more every few
> > or several seconds (depending on the situation) based on my algorithm

That seems problematic to me.  It seems that since there will be a
great many time jumps that tasks expecting to see every second such as
cron and other processes will lose those times.  If you are going to
jump the time I think that undesirable but fewer jumps more desirable
than many jumps.  The lessor evil being fewer I would make one big
jump and stop there.

I have never seen a VM be that much out of sync on time.  But then I
recently saw a posting on a qemu mailing list from someone who was
moving running VMs from one host system to another (a cool feature
btw) and there was a problem because the time multipliers were not the
same on the different hardware.  I don't remember the details now.  A
patch was proposed to allow mitigating it.  Your description sounds
like it may be due to a similar problem?  That may be enough for you
to research the solution.

Bob