[opensuse-virtual] should ntp be governing the clock in a guest system?
Continued from opensuse-factory:
Probably other virtualization technology have the same issue, do not use ntp. I do not know for certain.
With xen, my guests run ntpd and have xen.independent_wallclock=1.
And both host and guest try to adjust the speed of the mother board hardware clock chip? (not the bios clock, that's a very different one).
No, only the Dom0 does that. The guests are independent when you use xen.independent_wallclock=1.
http://www.novell.com/documentation/vmserver/config_options/data/b9qzhq5.htm...
But if you run the ntp daemon on guests, it tries to adjust the speed of the clock there. That's how it works.
Of course, that's what you want it to do. You want the guest clock synchronized. It would appear to be a good idea to have ntp on the xen Dom0 govern the clock for all the guests, but in my experience systemd does not like that. I looked into in March 2015 when I was virtualising some systems, and found the Novell page above. The Xen FAQ: https://wiki.xen.org/wiki/Xen_FAQ_DomU also recommends running ntp in each DomU. Finally, Werner Flamme wrote:
When you install SAP systems on top of Xenified VMs, there is the recommendation to do the latter: disable the sync and run a separate ntpd in the DomU. This is also a recommendation for VMs inside a VMWare environment - the problem ist the same there.
Back in March last year I did ask what the typical practice was, but noone had any suggestions. -- Per Jessen, Zürich (25.2°C) http://www.dns24.ch/ - free dynamic DNS, made in Switzerland. -- To unsubscribe, e-mail: opensuse-virtual+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-virtual+owner@opensuse.org
On 2016-09-02 16:00, Per Jessen wrote:
Continued from opensuse-factory:
(by the way, this was https://bugzilla.novell.com/show_bug.cgi?id=773323)
But if you run the ntp daemon on guests, it tries to adjust the speed of the clock there. That's how it works.
Of course, that's what you want it to do. You want the guest clock synchronized. It would appear to be a good idea to have ntp on the xen Dom0 govern the clock for all the guests, but in my experience systemd does not like that.
Yes, we want the clock synchronized, but not by adjusting the speed on guests. Just copied from the host. It adds load on the virtualized hardware. I know that vmware does recommends not running ntpd in guests, but instead use: tools.syncTime = "TRUE" I'll try again to find a source for this.
I looked into in March 2015 when I was virtualising some systems, and found the Novell page above.
The Xen FAQ: https://wiki.xen.org/wiki/Xen_FAQ_DomU also recommends running ntp in each DomU.
Finally, Werner Flamme wrote:
When you install SAP systems on top of Xenified VMs, there is the recommendation to do the latter: disable the sync and run a separate ntpd in the DomU. This is also a recommendation for VMs inside a VMWare environment - the problem ist the same there.
Back in March last year I did ask what the typical practice was, but noone had any suggestions.
This is against what I read the vmware people say. -- Cheers / Saludos, Carlos E. R. (from 13.1 x86_64 "Bottle" at Telcontar)
On 2016-09-02 16:48, Carlos E. R. wrote:
On 2016-09-02 16:00, Per Jessen wrote:
Continued from opensuse-factory:
(by the way, this was https://bugzilla.novell.com/show_bug.cgi?id=773323)
But if you run the ntp daemon on guests, it tries to adjust the speed of the clock there. That's how it works.
Of course, that's what you want it to do. You want the guest clock synchronized. It would appear to be a good idea to have ntp on the xen Dom0 govern the clock for all the guests, but in my experience systemd does not like that.
Yes, we want the clock synchronized, but not by adjusting the speed on guests. Just copied from the host. It adds load on the virtualized hardware.
I know that vmware does recommends not running ntpd in guests, but instead use:
tools.syncTime = "TRUE"
I'll try again to find a source for this.
I have not found the paper where I go that info; instead got another that differs.
One old document was http://www.vmware.com/info?id=34 but that link no longer works.
I read a note on one of the posts to google for vmware_timekeeping.pdf, which I found here:
Carlos E. R. wrote:
On 2016-09-02 16:00, Per Jessen wrote:
Continued from opensuse-factory:
(by the way, this was https://bugzilla.novell.com/show_bug.cgi?id=773323)
I didn't know that one, but it seems to be about local vs UTC time?
But if you run the ntp daemon on guests, it tries to adjust the speed of the clock there. That's how it works.
Of course, that's what you want it to do. You want the guest clock synchronized. It would appear to be a good idea to have ntp on the xen Dom0 govern the clock for all the guests, but in my experience systemd does not like that.
Yes, we want the clock synchronized, but not by adjusting the speed on guests. Just copied from the host. It adds load on the virtualized hardware.
Yes, the obvious way seems to be to just leave the guests to trust the synchronized clock from the Dom0. The load is negligible, especially on a typical virtual host. -- Per Jessen, Zürich (24.8°C) http://www.dns24.ch/ - free dynamic DNS, made in Switzerland. -- To unsubscribe, e-mail: opensuse-virtual+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-virtual+owner@opensuse.org
Per Jessen wrote:
Carlos E. R. wrote:
On 2016-09-02 16:00, Per Jessen wrote:
Continued from opensuse-factory:
(by the way, this was https://bugzilla.novell.com/show_bug.cgi?id=773323)
I didn't know that one, but it seems to be about local vs UTC time?
But if you run the ntp daemon on guests, it tries to adjust the speed of the clock there. That's how it works.
Of course, that's what you want it to do. You want the guest clock synchronized. It would appear to be a good idea to have ntp on the xen Dom0 govern the clock for all the guests, but in my experience systemd does not like that.
Yes, we want the clock synchronized, but not by adjusting the speed on guests. Just copied from the host. It adds load on the virtualized hardware.
Yes, the obvious way seems to be to just leave the guests to trust the synchronized clock from the Dom0. The load is negligible, especially on a typical virtual host.
I don't know if anybody cares much, but on a xen guest running Leap422b1 with ntp disabled, I no longer see those "Time has been changed" messages apart from once or twice. (I used to have them twice a minute). I'll leave it running for a while and see what happens. Does anyone here have an opinion on the matter? -- Per Jessen, Zürich (21.1°C) http://www.hostsuisse.com/ - dedicated server rental in Switzerland. -- To unsubscribe, e-mail: opensuse-virtual+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-virtual+owner@opensuse.org
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 On 2016-09-04 18:39, Per Jessen wrote:
I don't know if anybody cares much, but on a xen guest running Leap422b1 with ntp disabled, I no longer see those "Time has been changed" messages apart from once or twice. (I used to have them twice a minute). I'll leave it running for a while and see what happens.
Does anyone here have an opinion on the matter?
That's what I see on my vmware player guest, too. I'd guess that systemd has its own clock adjustment service running and it doesn't like ntp touching the clock as well. What that service might be, I don't know. - -- Cheers / Saludos, Carlos E. R. (from 13.1 x86_64 "Bottle" (Minas Tirith)) -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) iF4EAREIAAYFAlfMcSAACgkQja8UbcUWM1xhXQD9GIFGkFzgyPrlX3zxE3u8Z8ky gEiX/xV5qwEwNlVQ85EA/29UAjQiWOFVquMvShCp2DmbhcoH9WRN3L7BZjebmiJM =yEmt -----END PGP SIGNATURE----- -- To unsubscribe, e-mail: opensuse-virtual+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-virtual+owner@opensuse.org
Carlos E. R. wrote:
-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256
On 2016-09-04 18:39, Per Jessen wrote:
I don't know if anybody cares much, but on a xen guest running Leap422b1 with ntp disabled, I no longer see those "Time has been changed" messages apart from once or twice. (I used to have them twice a minute). I'll leave it running for a while and see what happens.
Does anyone here have an opinion on the matter?
That's what I see on my vmware player guest, too.
I'd guess that systemd has its own clock adjustment service running and it doesn't like ntp touching the clock as well. What that service might be, I don't know.
I doubt that very much. Besides, why should openSUSE have ntp running by default then? I'm beginning to wonder - if Dom0 is actually a little of out sync, ntp would slowly be adjusting the clock, and I guess systemd would notice that. - if Dom0 is actually sync'ed, no adjustment is needed, nothing for systemd to notice. -- Per Jessen, Zürich (15.4°C) http://www.dns24.ch/ - free dynamic DNS, made in Switzerland. -- To unsubscribe, e-mail: opensuse-virtual+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-virtual+owner@opensuse.org
On 2016-09-05 08:47, Per Jessen wrote:
Carlos E. R. wrote:
I'm beginning to wonder
- if Dom0 is actually a little of out sync, ntp would slowly be adjusting the clock, and I guess systemd would notice that.
I doubt that systemd would notice unless carefully watching for it, because normally ntpd adjusts the speed of the clock, not the value of the clock itself. Programs can not notice that unless they compare the clock with some other reference and see the difference. Programs can only notice if the value of the clock change. If it jumps suddenly skipping intermediate values. -- Cheers / Saludos, Carlos E. R. (from 13.1 x86_64 "Bottle" at Telcontar)
Carlos E. R. wrote:
On 2016-09-05 08:47, Per Jessen wrote:
Carlos E. R. wrote:
I'm beginning to wonder
- if Dom0 is actually a little of out sync, ntp would slowly be adjusting the clock, and I guess systemd would notice that.
I doubt that systemd would notice unless carefully watching for it,
I agree, so it clearly does. I suspect there is some event that is triggered when time make a jump or time is not monotone. -- Per Jessen, Zürich (17.6°C) http://www.dns24.ch/ - free dynamic DNS, made in Switzerland. -- To unsubscribe, e-mail: opensuse-virtual+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse-virtual+owner@opensuse.org
participants (2)
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Carlos E. R. -
Per Jessen