NTP switch in gnome-control-center is broken

[Miroslav Lichvar]

On Wed, Oct 08, 2014 at 11:04:20AM -0500, Michael Catanzaro wrote:
> Looks like F21 is about to get a git snapshot of systemd, but with the
> NTP change patched out. While there's no urgency for F21, there's also
> no particular reason to leave this broken in rawhide for ages, so I
> propose we drop chronyd beginning with F22. I'm not opposed to keeping
> chrony around if we can integrate it with timedated, but the path of
> least resistance is certainly to drop it. Any objections?

I understand that maintainers don't like keeping Fedora specific
patches in their packages, but fixing timedated to control chronyd
instead of timesyncd in the current code is trivial. It doesn't even
require a patch, it can be done with a sed command.

sed -i 's|systemd-timesyncd.service|chronyd.service|' src/timedate/timedated.c

As for switching to timesyncd as default NTP client, I'm familiar
with the code. It's a minimal SNTP client based on the ConnMan SNTP
implementation. I've tested it, found and fixed some bugs, and also
made some small improvements. In its current state, however, I'm not
sure it would be a good default client in a distribution like Fedora.

On a LAN with trusted NTP servers it should be fine, but when using
public NTP servers on internet, which is what we do by default, or
not connected permanently I wouldn't recommend it just yet. There
were some good reasons when we switched from ntpd to chronyd in Fedora
16 [1] and from what I can tell it has worked very well so far. With
timesyncd I think we would be worse off than we started.

For those who didn't see the thread about making timedated
configurable for other NTP services on the systemd list [2], some of
the issues with timesyncd are:

- reliability, timesyncd is an SNTP client and not a full NTP client,
  it doesn't compare data from multiple serverss, so it's not able to
  detect broken servers and will blindly follow almost any reply
- no guarantees on monotonicity of the clock, time jumping back and
  forth with network connections suffering from bufferbloat
- no integration with NetworkManager, unaware of NTP servers from DHCP
- dependency on systemd-networkd, which is not enabled by default

[1] http://fedoraproject.org/wiki/Features/ChronyDefaultNTP
[2] http://lists.freedesktop.org/archives/systemd-devel/2014-August/022367.html

-- 
Miroslav Lichvar