Re: ntp questions
On Sunday 15 March 2020 08:33:30 G.W. Haywood wrote:
> Hi there,
>
> On Sun, 15 Mar 2020, Gene Heskett wrote:
> > ... What I wanted was to sync to the debian servers with this
> > machine, and then let it broadcast to the rest of the local network,
>
> Some observations about ntpd and NTP in general:
>
> 1. Unless you're running a time laboratory, don't use ntpd. Use
> chrony. In my experience it's much more forgiving, easier to configure
> and does the job it needs to do for those of us who are happy with
> accuracies in the order of a couple of milliseconds. I used ntpd for
> decades. Since I started using chrony a few years ago it has been
> *much* less trouble, and I no longer feel the need to be subscribed to
> a 'time' mailing list. This has the happy side-effect that I also
> don't need to worry about being berated by some NTP guru for using a
> Linux box as a time server.
>
> 2. If you must use your own server, in addition to them use a pool of
> remote time servers such as provided by Debian. You really don't want
> the time on your network hunting around following a single rogue box
> after it unexpectedly rebooted with the wrong time. Please use the
> 'makestep' chrony directive on machines which aren't running 24/7; by
> all means use prefer, iburst etc. if you feel the need.
>
> 3. Enable the (three) chrony logs and look at them often - especially
> just after boot, so you get a feel for how quickly you can expect the
> time to be recovered. It should be no more than a couple of minutes.
>
> 4. Use e.g. Nagios/Icinga to monitor things like this. I can let you
> have some example graphs privately, and configuration snippets too if
> it will help. If the time on any box goes out of spec. I get an email
> within minutes.
>
> > I can add more stratum 2 stuff to this machine, and I can move this
> > machine to above the debian servers in the ntp.conf if order helps.
>
> 5. You shouldn't worry about strata yourself, let the servers do that.
> Low strata don't necessarily equate to high accuracy, and vice-versa.
>
> 6. For a few $currency_units you can add a RTC module to any device
> which doesn't have one. I prefer to keep the hardware clock on UTC,
> and let the OS and/or application software worry about any timezones,
> and especially about changes such as Daylight Saving. With a bit of
> effort, the hardware clock will see only the (very) occasional leap
> second adjustments.
>
> 7. See https://en.wikipedia.org/wiki/NTP_server_misuse_and_abuse for
> many ways of inadvertently abusing NTP, which you should avoid, and a
> few ways of being led down the garden path too (also to be avoided).
>
> > currently 3 amd64 boxes, and the rpi4.
>
> I note with interest that you're using a Raspberry Pi 4. In my recent
> experience these are particularly flaky compared with other Pis - and,
> well, everything else. They really hate disturbances on the USB ports
> for example and will hang/crash/reboot/remount-read-only/trash-the-fs
> without warning if you should happen to plug in a second USB camera or
> disc. It seems to me it's the power conditioning that's at the root
> of this, but at the moment I haven't worked with them for long enough
> to say much more than that. I'm using Pi 3s for things like my backup
> servers, they seem to be much more reliable. I'm writing this mail on
> a Pi3b+ which has been my desktop thin client and also a backup server
> for some months. It's never put a foot wrong. Even the one venerable
> Pi 2 that we have here is more reliable than the 4. The Zeros seem OK
> if you don't overtax them, but we tend to use them just for gadgetry.
> Or rather _did_ use them. AFAICT at the moment you can't actually buy
> one anywhere, and this situation does not seem to be improving; so any
> time spent designing with Zeros seems to have been pretty much wasted.
This instant reboot thing is the first time I have had anything happen to
any pi in the 3 or higher category. With a ups, until now, rebooting has
absolutely been at my pleasure. I can't say the same for my 3 wintel
boxes running other machines. I went to a pi4 for this because the pi3
was doing a pretty good jub but dragging its tongue on the floor,
whereas the pi4, at a fixed 800MHz, is effectively parked in a beach
chair under an umbrella, feet up and Martini in hand, up till now.
Cheers, Gene Heskett
--
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
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- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/gene>
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