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Time Keeping in instances

asked 2013-04-15 17:43:03 -0500

slashterix gravatar image

Is it important to run ntpd in guest instances? Or is their hardware clock kept up with the hosts clock (which is kept up with ntpd)

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answered 2013-04-16 14:22:39 -0500

mikal gravatar image

From the KVM manpage (so, specifically about that hypervisor):

       By default the RTC is driven by the host system time. This allows to use the RTC as
       accurate reference clock inside the guest, specifically if the host time is smoothly
       following an accurate external reference clock, e.g. via NTP.  If you want to isolate the
       guest time from the host, you can set clock to "rt" instead.  To even prevent it from
       progressing during suspension, you can set it to "vm".

So, if your hosts are running NTP you shouldn't need NTP in the guest.

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Is there an easy way to find out if the hosts are running NTP without having to open a support ticket?

colan gravatar imagecolan ( 2018-02-14 19:21:11 -0500 )edit

Looks like the docs say to set up the host nodes with NTP so assuming your provider is following the manual, NTP should be running on them. See .

colan gravatar imagecolan ( 2018-02-14 19:25:33 -0500 )edit

answered 2013-04-16 08:09:01 -0500

updated 2013-04-16 08:09:26 -0500


It is not necessary to run ntpd in guest vms for OpenStack to work correctly, that doesn't affect OpenStack at all - unless you don't mess OpenStack's nodes time.

If the applications running in your guest need NTPD then you might want to install it, otherwise, it is not required. It all depends on what you need to do in the guest VM.


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I know that some virtualization systems (VMWare) are quite bad at keeping the wall clock in a guest accurate, while others handle it quite well. Primarily I just don't want my guest clocks drifting by several minutes. Does OpenStack keep the wall clocks in its guests accurately?

slashterix gravatar imageslashterix ( 2013-04-16 11:32:19 -0500 )edit

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Asked: 2013-04-15 17:43:03 -0500

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Last updated: Apr 16 '13