On Sun, 2017-02-05 at 12:30 -0500, Robert Moskowitz wrote:
>
> On 02/05/2017 11:58 AM, J Martin Rushton wrote:
> > On 05/02/17 16:15, Richard wrote:
> > > > Date: Sunday, February 05, 2017 10:26:05 -0500
> > > > From: Robert Moskowitz <rgm@xxxxxxxxxxxxxxx>
> > > >
> > > > I have read:
> > > > http://thegeekdiary.com/centos-rhel-7-chrony-vs-ntp-differences
> > > > -bet
> > > > ween-ntpd-and-chronyd/
> > > >
> > > > My server is up all the time and will serve time to internal
> > > > systems (via DHCP options).
> > > >
> > > > Caveat is that my server is an armv7 (Cubieboard2) which does
> > > > not
> > > > have an RTC (no battery). So whenever the system boots, the
> > > > time
> > > > is ZERO (Dec 31, 1969 or some such).
> > > >
> > > > Chrony fixes this really fast; shortly after boot the time is
> > > > good.
> > > > Chrony CAN be configed as an internal time server. But chrony
> > > > does
> > > > not seem to step the clock for any adjustments needed. It is
> > > > more
> > > > important that this systems time be right all the time than to
> > > > avoid clock steps.
> > > >
> > > > This brings me back to NTP, which normally takes hours to bring
> > > > the
> > > > time from ZERO to current, but keeps the time correct.
> > > >
> > > > So:
> > > >
> > > > Can Chrony check the time, say once a day?
> > > >
> > > > Or can NTP make a BIG time jump all at once (on system
> > > > restart)?
> > >
> > > Where I have somewhat similar issues, I have historically used a
> > > crontab "@reboot" entry to call ntpdate which gets the clock set
> > > correctly. From there ntp keeps it in sync.
> > >
> > > This can now be accomplished with ntpd, and ntpdate is threatened
> > > with depreciation/retirement. See the top of the ntpdate man page
> > > for
> > > more details.
> > >
> >
> > The NTP configuration option you may be after is "tinker panic 0"
> > which
> > allows NTP to make big jumps as often as required. See
> > ntp_misc(5).
> > There is a related discussion with making VMs take big jumps at
> > https://www.centos.org/forums/viewtopic.php?f=16&t=61186&p=258254#p
> > 258254
>
> Thanks. I will look at this. All I was seeing was to use burst and
> iburst, but they would not make the really big jump needed after
> boot.
>
>
With NTP you could use the ntpdate.service as well as/ before
ntpd.service. the former is supposed to set the clock once BEFORE ntpd
is started.
See: https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_L
inux/6/html/Deployment_Guide/s1-Configure_ntpdate_Servers.html
Ntpdate seems to work on RHEL/Centos 7 as well...
/Louis
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