Date: Wed, 23 Sep 2015 10:35:54 -0700 From: Tim Kientzle <tim@kientzle.com> To: Poul-Henning Kamp <phk@freebsd.org> Cc: hackers@freebsd.org Subject: Re: What IS the right NTP behaviour ? Message-ID: <F6AF299A-17B1-44DF-B025-B8FA0BC833D4@kientzle.com> In-Reply-To: <39337.1442999127@critter.freebsd.dk> References: <39337.1442999127@critter.freebsd.dk>
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I like your outline here. One concern I keep running into: Using NTP in VMs that are frequently = suspended/resumed. Though I suppose this may be covered by your = 'workstation' scenario (just step it after VM resume when you see the = large skew). Tim > On Sep 23, 2015, at 2:05 AM, Poul-Henning Kamp <phk@freebsd.org> = wrote: >=20 > As you probably know I'm working on a new NTP client called Ntimed. >=20 > It is no surprise that people have different expectations of how > timekeeping should behave, and I'm trying to figure out > what Do What I Want is. >=20 > I think I have identified three variations of "DWIW", which I have > named "eCommerce", "SCADA" and "Workstation" >=20 > Please let me know (private email to keep list noise down) if your > needs would not be served by any of these three variations or for > that matter any other comment or input on this topic. >=20 > Thanks >=20 > Poul-Henning >=20 >=20 > eCommerce > --------- >=20 > Correct system time is mandatory. >=20 > Bootup fails if correct time cannot established. > What do we mean by "fails" ? > Does it hang until success ? > Does it fail into single-user ? > Does it raise a big red flag ? >=20 > Stepping time after bootup is *never* allowed. > If time drifts out of tolerance: > Raise Alarm > How ? > Signal init(8) into single-user mode ? > Slew clock, no matter how far. > Syslog periodically how wrong system time is >=20 > SCADA > ----- >=20 > We don't need the system clock to be on time, as long as > we know exactly how wrong it is. >=20 > Startup should be as quick and reliable as possible. > Configurable timer for how long we hold up startup. >=20 > Startup step only allowed during this time interval. >=20 > Stepping time after bootup is never allowed. > If time drifts out of tolerance: > Slew clock, no matter how far. > Syslog periodically how wrong system time is > Raise Alarm (optional) > How ? >=20 > Workstation > ----------- >=20 > Startup should be fast-ish >=20 > Steps are allowed any time necessary > suspend/resume > change in network topology > clock drift >=20 > --=20 > Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 > phk@FreeBSD.ORG | TCP/IP since RFC 956 > FreeBSD committer | BSD since 4.3-tahoe > Never attribute to malice what can adequately be explained by = incompetence. > _______________________________________________ > freebsd-hackers@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-hackers > To unsubscribe, send any mail to = "freebsd-hackers-unsubscribe@freebsd.org" >=20
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