| RE: [chrony-users] Isolated time domains |
[ Thread Index |
Date Index
| More chrony.tuxfamily.org/chrony-users Archives
]
On Thu, 5 Dec 2013, Chris Dore wrote:
On Thu, Dec 5 2013, Bill Unruh wrote:
Eg, he says that he wants to keep all of the computers to within 1 sec. But
what happens if one of the clients suddenlyfinds itself 3 hours out? Are all of
the other clients then supposed to go out as well to keep themselves in sync
with that client? How would they do that? And if not, why is the server
special that all should run after its crazyness?
The clients should, and do already, follow the server no matter how "crazy" it may seem to the outside world. The server in a single site location is the source of truth for what UTC is. All clients on that site must obey or not participate in operations. In fact, these clients will already make whatever jumps in time are needed to bring themselves in line with the server (usually as part of connection startup). If one client of the server decided that it knew better than the server and adjusted to some other reference of UTC than it just functionally won't work. That's why the server is special.
"Just functionaly won't work" means what? If |client time-server time| > x
seconds -> shut down client?
So, in order to avoid introducing risk into what is already operating, I am looking for a way to slowly move the server's time to UTC as indicated by a remote NTP server while the clients happily follow along. For server's with more extreme offsets from UTC, they can be manually stepped when operationally appropriate.
How slowly? One of the features of chrony is that it will slew a clock quickly
to bring it in line (up to 100000 PPM if necessary --> .9sec/sec drift rate.
Since ntpd refuses to move faster than 500PPM, you must use chrony on all your
clients or there is no way they can keep up. If you use chrony on your server,
and ntpd on your clients you will have to persuade chrony to keep its rate
well below 500PPM which will mean it will take about a year to get rid of a 3
hr offset in the master.
Also if you use ntpd on your clients, it will jump the time if it finds itself
sure that it has an offset of greater than 0.128 sec. Chrony can also be set up to jump
the time if you want.
As an experiment, I've got two instances of chronyd running on a server. One instance is sourcing the external ntp servers and taking care of the server's local clock. The second instance, is just serving up the local clock to the clients (on a different UDP port). This is producing what I've been describing, although I'm not a big fan of having two instances running since I don't understand the chronyd/NTP internals well enough to know of any gotchas that may be hiding. Also, requiring the use of a non-standard port is less than ideal, in case an ntp client doesn't support it.
Both ntpd and chrony support non-standard ports.
Are you planning on using anything other than ntpd or chrony?
Chris
--
To unsubscribe email chrony-users-request@xxxxxxxxxxxxxxxxxxxx
with "unsubscribe" in the subject.
For help email chrony-users-request@xxxxxxxxxxxxxxxxxxxx
with "help" in the subject.
Trouble? Email listmaster@xxxxxxxxxxxxxxxxxxxx.
--
William G. Unruh | Canadian Institute for| Tel: +1(604)822-3273
Physics&Astronomy | Advanced Research | Fax: +1(604)822-5324
UBC, Vancouver,BC | Program in Cosmology | unruh@xxxxxxxxxxxxxx
Canada V6T 1Z1 | and Gravity | www.theory.physics.ubc.ca/
--
To unsubscribe email chrony-users-request@xxxxxxxxxxxxxxxxxxxx
with "unsubscribe" in the subject.
For help email chrony-users-request@xxxxxxxxxxxxxxxxxxxx
with "help" in the subject.
Trouble? Email listmaster@xxxxxxxxxxxxxxxxxxxx.