Xen users - Nov 2007 - dom0 and domU differs after ntpdate

Hi all,
I''m experiencing problems with time: after I sync time both into dom0
and
dom1 with public ntp servers, times are not the same.
Do you have the same problem?
Thanks

Marco


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Marco Strullato wrote:
> Hi all,
> I''m experiencing problems with time: after I sync time both into
dom0
> and dom1 with public ntp servers, times are not the same.
> Do you have the same problem?
> Thanks
>
> Marco
>
Why would you run NTP on a DomU? You''d have to make the systems run 
independent clocks, and that''s begging for trouble.

But there are references to adjusting 
/proc/sys/xen/independent_wallclock for such settings.

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I''m sorry, I think I don''t well understand what you wrote.
could you be more
clear?
why you suggest me not to run ntp on domUs? Maybe I don''t know how xen
works
with ntp....

Thanks

Marco




2007/11/6, Nico Kadel-Garcia <nkadel@gmail.com>:
>
> Marco Strullato wrote:
> > Hi all,
> > I''m experiencing problems with time: after I sync time both
into dom0
> > and dom1 with public ntp servers, times are not the same.
> > Do you have the same problem?
> > Thanks
> >
> > Marco
> >
> Why would you run NTP on a DomU? You''d have to make the systems
run
> independent clocks, and that''s begging for trouble.
>
> But there are references to adjusting
> /proc/sys/xen/independent_wallclock for such settings.
>

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Marco Strullato wrote:
> I''m sorry, I think I don''t well understand what you
wrote. could you
> be more clear?
> why you suggest me not to run ntp on domUs? Maybe I don''t know how
xen
> works with ntp....
>
> Thanks
>
> Marco
All NTP daemons work by manipulating a time offset, an offset between 
the clock time reported by the hardware clock and the actual time as 
deduced from NTP servers. And they also have a second offset, one that 
allows them to retain a record over some period of the amount of drift 
that consistently happens and adjust for it. It''s described here:

    http://en.wikipedia.org/wiki/Network_Time_Protocol

OK? Now imagine that you''re a surveyor doing careful work, and you put 
some markers down in a convenient place, and you measure how long things 
are, and where they are, and you make a nice map, and you record where 
your markers very carefully so you can rely on them.

Now imagine some other surveyor starts taking and using your marker, and 
*keeps moving it* when you''re not looking. You can never hope to get
all
your maps done accurately while this is going on.

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After echo 1 > /proc/sys/xen/independent_wallclock
and an ntpdate on each server the time is right.

Thanks

Marco

2007/11/6, Nico Kadel-Garcia <nkadel@gmail.com>:
>
> Marco Strullato wrote:
> > I''m sorry, I think I don''t well understand what you
wrote. could you
> > be more clear?
> > why you suggest me not to run ntp on domUs? Maybe I don''t
know how xen
> > works with ntp....
> >
> > Thanks
> >
> > Marco
> All NTP daemons work by manipulating a time offset, an offset between
> the clock time reported by the hardware clock and the actual time as
> deduced from NTP servers. And they also have a second offset, one that
> allows them to retain a record over some period of the amount of drift
> that consistently happens and adjust for it. It''s described here:
>
>     http://en.wikipedia.org/wiki/Network_Time_Protocol
>
> OK? Now imagine that you''re a surveyor doing careful work, and you
put
> some markers down in a convenient place, and you measure how long things
> are, and where they are, and you make a nice map, and you record where
> your markers very carefully so you can rely on them.
>
> Now imagine some other surveyor starts taking and using your marker, and
> *keeps moving it* when you''re not looking. You can never hope to
get all
> your maps done accurately while this is going on.
>

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i have the UTC version, so i''ve got 2h late.
it''s 13h instead of 15h, right now for me.

how could i correct this, please?


On Nov 6, 2007 1:51 PM, Marco Strullato <marco.strullato@gmail.com>
wrote:
> After echo 1 > /proc/sys/xen/independent_wallclock
> and an ntpdate on each server the time is right.
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Hi,

On Tue, Nov 06, 2007 at 03:03:37PM +0100, Kanchana
wrote:
> i have the UTC version, so i''ve got 2h late.
> it''s 13h instead of 15h, right now for me.
> 
> how could i correct this, please?
Set the time zone properly inside the domU, the procedure for which
is different depending on what OS and distribution you are running,
but is generally the same as what you would do if not running Xen.

Cheers,
Andy


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