Michal Privoznik wrote: > On 20.09.2014 01:36, Jim Fehlig wrote: >> Martin Kletzander wrote: >>> On Fri, Sep 19, 2014 at 02:37:12PM -0600, Jim Fehlig wrote: >>>> Michal Privoznik wrote: >>>>> On 08.09.2014 18:30, Jim Fehlig wrote: >>>>>> If an NTP server is configured on the host, it is possible for >>>>>> libvirt-guests to start before the NTP service, in which case >>>>>> guest clocks won't be synchronized to the host clock. >>>>>> >>>>>> Add ntp-wait.service to "After" in libvirt-guests systemd service >>>>>> file, ensuring NTP has synchronized the host clock before starting >>>>>> any guests. >>>>>> >>>>>> Signed-off-by: Jim Fehlig <jfehlig@xxxxxxxx> >>>>>> --- >>>>>> tools/libvirt-guests.service.in | 2 +- >>>>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>>>> >>>>>> diff --git a/tools/libvirt-guests.service.in >>>>>> b/tools/libvirt-guests.service.in >>>>>> index d8d7adf..226b3bd 100644 >>>>>> --- a/tools/libvirt-guests.service.in >>>>>> +++ b/tools/libvirt-guests.service.in >>>>>> @@ -1,6 +1,6 @@ >>>>>> [Unit] >>>>>> Description=Suspend Active Libvirt Guests >>>>>> -After=network.target libvirtd.service >>>>>> +After=network.target libvirtd.service ntp-wait.service >>>>>> Documentation=man:libvirtd(8) >>>>>> Documentation=http://libvirt.org >>>>>> >>>>>> >>>>> >>>>> Well, guest can have their own ntp-client (and in most cases they do, >>>>> right?). >>>> >>>> I think most do, but know of at least two users who want to use >>>> kvmclock >>>> with no ntp in the guests :). >>>> >>> >>> I'm sure there are way more users without ntp clients inside their >>> guests. I'm just wondering what's the difference when libvirt-guests >>> starts before or after ntp has synchronized their clocks. Is it that >>> they have the time reset to a little bit inaccurate time? Or are they >>> off way too much? >> >> They are off by the ntp adjustment. As I understand it, the guests >> start and read the host clock, which is later adjusted by ntp. >> >>> >>>>> I mean, since guests can be paused, saved & restored back, their time >>>>> is often off. So the best is to have an ntp-client running inside the >>>>> guest. >>>> >>> >>> Yes, but if it's way off, ntp will refuse to update the time; that's >>> why we are resetting the time, isn't it? >>> >>>> Yep. I mentioned this, but seems they don't use save, restore, >>>> migrate, >>>> et. al., since it wasn't a concern. But I'm fine handling this >>>> downstream. Thanks! >>>> >>> >>> Well, if they use libvirt-guests, they use at least save/restore :) >> >> They have ON_SHUTDOWN=shutdown. >> >>> >>> Unfortunately I'm not very familiar with systemd files, but my guess >>> is that After=ntp-wait.service means it should be started after the >>> time is synchronized if and only if the ntp-wait.service unit is >>> enabled, otherwise it doesn't require it. >> >> Yes, this is my understanding too. > > And so is mine. The only concern I have is that syncing time on cold > boot of the host may take ages. Yep, I have this concern too. So I dug a bit further and see that ntp-wait (a perl script) scrapes the output of `ntpq -c "rv 0`, waiting for leap_alarm to change to leap_none, leap_add_sec, or leap_del_sec. On my test system, this took ~16min on cold boot :-(. ntp-wait.service failed in the meantime, since it by default calls /usr/sbin/ntp-wait with options to only wait 10min. > But on the other hand, it's better to start domains later and with > correct time than start asap with inaccurate time. ACK then, Given the above observations, I'll wait to see if you change your mind. Regards, Jim -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list