| Isaac Bennetch on 8 Jul 2015 11:52:11 -0700 |
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| Re: [PLUG] ntp |
JP and others, thanks for the great information. I knew using ntpdate was a workaround but looks like I should reevaluate that choice and do it the right way. Best, Isaac > On Jul 8, 2015, at 2:40 PM, JP Vossen <jp@jpsdomain.org> wrote: > > Ohhh, that's...bad... > > Running `ntpdate` periodically can be dangerous and is the WRONG answer > if the server hosts any kind of database or anything time sensitive > (even arguably just logs). Large jumps forward in time can be bad > enough, but if it adjusts backwards it can really be a problem. > > Just use NTP, do not use ntpdate [1]. > https://lists.debian.org/debian-user/2002/12/msg04091.html > https://www.redhat.com/archives/nahant-list/2005-December/msg00009.html > > Aside from the general wrongness of the answer, `ntpdate` is deprecated: > http://support.ntp.org/bin/view/Dev/DeprecatingNtpdate > > That said, VMs can be tricky. VMware tools has a "keep in sync" option > but even they recommend using NTP: > http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1006427 > "VMware recommends using NTP instead of VMware Tools periodic time > synchronization. NTP is an industry standard and ensures accurate > timekeeping in your guest..." > > I can't speak to other virtualization, but I'm positive solutions exist > if NTP isn't the right answer. > > Once in sync NTP should not "slip" and if it does it should certainly > not slip more than 1,000 seconds ([1] and `man ntpd`, then search for > -g). See also `ntptrace` `ntpstat` or `ntpq -pn` depending on distro > flavor and age. > > > [1] You used to use `ntpdate` at boot time to get the system clock close > enough that NTP would keep it in sync. Probably some distros still do that. > > NTP itself will refuse to adjust larger than the "panic threshold," > which is 1000s by default. It used to not be to clear about why it > wasn't working, and ntpdate used to be more clear. That has hopefully > improved, but I can't swear to it. My NTP, virtual or otherwise, Just > Works. > > >> On 07/08/2015 02:35 PM, Eric Lucas wrote: >> About 2 years ago I worked, briefly, with some systems using ntp. Turns >> out if the time is off by some small amount (less than a minute IIRC), > > 1,000 seconds per the man page I was just looking at in Debian 7. > >> it simply stops changing the target system's time because it "thinks" >> something is drastically wrong. >> >> Seems like a cron job to re-sync is a good idea to me. >> >> Eric >> >> On Wed, Jul 8, 2015 at 2:24 PM, Keith C. Perry >> <kperry@daotechnologies.com <mailto:kperry@daotechnologies.com>> wrote: >> >> I hope you're saying that in jest Walt. In my experience ntpd slips >> way too much. Once clocks get out of sync by too much ntpd won't >> nudge it back and that can happens more often than not on >> interactive and poorly tuned HPC nodes. >> >> You can have the same issue on system boots. >> >> My apologies if I'm misinterpreting tone. >> >> >> ----- Original Message ----- >> From: "Walt Mankowski" <waltman@pobox.com <mailto:waltman@pobox.com>> >> To: plug@lists.phillylinux.org <mailto:plug@lists.phillylinux.org> >> Sent: Wednesday, July 8, 2015 2:15:39 PM >> Subject: Re: [PLUG] ntp >> >> But...but... >> >> You do realize that's essentially what ntpd does, only ntpd does it >> way better, right? >> >> Right? >> >>> On Wed, Jul 08, 2015 at 01:37:59PM -0400, Keith C. Perry wrote: >>> That's what I do. Run "ntpdate us.pool.ntp.org >> <http://us.pool.ntp.org>" every 4 to 6 hours on critical / core systems. >>> >>> >>> >>> From: "Bill East" <wm.east@gmail.com <mailto:wm.east@gmail.com>> >>> To: "Philadelphia Linux User's Group Discussion List" >> <plug@lists.phillylinux.org <mailto:plug@lists.phillylinux.org>> >>> Sent: Wednesday, July 8, 2015 1:35:29 PM >>> Subject: Re: [PLUG] ntp >>> >>> >>> >>> I just had to deal with a vendor installation which was about 4 >> seconds off the ntp server it was supposed to be synced with. Come >> to find out the vendor ran a ntpdate command once a day and the vm >> was drifting 4 seconds in the 24 hours between. Their solution was >> to run the command once an hour instead. >>>> On Jul 8, 2015 1:13 PM, "Eric Riese" < eric.riese@gmail.com >>> <mailto:eric.riese@gmail.com> > wrote: >>> >>> >>> >>> So I just noticed that my KVM server's clocks were way off. The >> host OS was 4 minutes behind time.gov <http://time.gov> and the >> guests were 4 minutes ahead of time.gov <http://time.gov> . >>> >>> Turns out the host did not have ntp installed at all. It's Ubuntu >> 12.04 and was installed as some sort of minimal installation. A sudo >> apt-get install ntp and five minutes later it's in good shape. >>> >>> The guests are debian installs from turnkeylinux.org >> <http://turnkeylinux.org> and they have ntp installed but were not >> running by default! >>> >>> To think, Google runs it's own internal NTP servers and had to >> spread the leap second out over a day, and I'm off by whole minutes! > > > Later, > JP > ----------------------------|:::======|------------------------------- > JP Vossen, CISSP |:::======| http://bashcookbook.com/ > My Account, My Opinions |=========| http://www.jpsdomain.org/ > ----------------------------|=========|------------------------------- > "Microsoft Tax" = the additional hardware & yearly fees for the add-on > software required to protect Windows from its own poorly designed and > implemented self, while the overhead incidentally flattens Moore's Law. > ___________________________________________________________________________ > Philadelphia Linux Users Group -- http://www.phillylinux.org > Announcements - http://lists.phillylinux.org/mailman/listinfo/plug-announce > General Discussion -- http://lists.phillylinux.org/mailman/listinfo/plug ___________________________________________________________________________ Philadelphia Linux Users Group -- http://www.phillylinux.org Announcements - http://lists.phillylinux.org/mailman/listinfo/plug-announce General Discussion -- http://lists.phillylinux.org/mailman/listinfo/plug