network time default, f23

Miroslav Lichvar mlichvar at
Tue Sep 1 09:26:03 UTC 2015

On Mon, Aug 31, 2015 at 12:48:37PM -0600, Chris Murphy wrote:
> On Mon, Aug 31, 2015 at 12:32 PM, Tomasz Torcz <tomek at> wrote:
> >   IMO FreeIPA should be changed to install use chrony as server,
> > as chrony is default since few Fedora releases.
> The pluses of chrony as an ntp client for Workstation are fairly
> clear. I don't know if there are significant advantages to chrony as
> an ntp server over ntpd.

Well, an NTP server is just an NTP client that is listening on port
123 and is willing to tell other hosts what time it currently thinks
it is. There is not much to it. A better NTP client should be also a
better NTP server. There are some server-specific differences between
chronyd and ntpd, but probably nothing so important that it would
decide what is a better default NTP server. See the "NTP server"
section here

chronyd doesn't implement server rate limiting (yet). It's not a high
priority. It may sound like a useful feature, but it often actually
increases the network traffic, because clients that send too many
requests are often the ones that will quickly send another request
when there is no reply from the server or it's told to reduce its
polling rate.

> >   Those are two different things. Timesyncd is simple SNTP client (plus
> > time restoration over reboot, for things without RTC).
> Is an exception needed for ARM where it's more common to find no RTC?
> That is, on ARM, have a different ntp client by default? Or is it
> possible to detect the lack of an RTC, and that causes chronyd/ntpd to
> be disabled, and timesyncd to be enabled?

With the -s option chronyd does restore time from the driftfile as a
fallback on machines without RTC, but should that be a responsibility
of the NTP client? I think there may be better places to do that.

On Debian, for instance, there is a separate fake-hwclock service, no
need to have an NTP client installed. Some systems support a fixrtc
option on the kernel command line to set the system time in initramfs
to the last mount time of the root filesystem.

Miroslav Lichvar

More information about the server mailing list