Date: Fri, 6 Mar 2015 00:24:57 -0800 From: Rick Thomas <rbthomas@pobox.com> To: FreeBSD Questions <freebsd-questions@freebsd.org>, questions@lists.ntp.org Cc: lokadamus@gmx.de Subject: Re: How to adjust clock frequency in FreeBSD 10.1 ? Message-ID: <61602B0F-2114-4B65-A576-34EDDF94EAFA@pobox.com> In-Reply-To: <54EDC2DD.8060307@gmx.de> References: <AE5A370C-A7F7-41D2-900D-B26521A2D705@pobox.com> <54EDC2DD.8060307@gmx.de>
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> On 02/12/15 04:09, Rick Thomas wrote: >> I=92ve got a machine with a really bad clock. When I run NTPD on it, >> the freq goes straight to 500.0 (over a period of a few days) and >> stays there, while the offset grows and grows. >>=20 >> I recently switched this machine from Debian Linux to FreeBSD >> (wanting to learn more about FreeBSD). Under Linux, I used >> adjtimex to modify the TICK value and (once I had converged on the >> right TICK value) NTP was able to stabilize the clock. >>=20 >> Is there an equivalent hack for FreeBSD? On Feb 25, 2015, at 4:41 AM, lokadamus@gmx.de wrote: > You can use a cronjob with ntpdate to synchronize your clock. > But ntpd shouldn=92t run, when ntpdate is used. >=20 As it turns out, current versions of ntpd will do as well as (actually = better than) periodic ntpdate =97 even under such adverse circumstances = as this machine. What it does is to attempt to slew the time using its = normal algorithms until the frequency adjustment gets pegged at 500ppm = and the offset is over 1 second. Then it steps the clock and starts the = game all over. This is better than previous versions of ntpd and xntpd. = They would get to that point and abort =97 on the theory that something = was acutely wrong and needed human operator attention. Current versions = at least have the option of plugging on as best as possible. So, with current ntpd, the system clock is never more than about 1 = second off from network time. And for a normal desktop machine (or ever a small-/home-office server) = that=92s really good enough and I should stop complaining. BUT=85 The trouble is, I=92m a =93time nut=94 and I keep this machine (and a = few others) around specifically as a test case =97 to prove that it *is* = possible to keep good time (sub millisecond offsets from a GPS server on = the same LAN) even with machines that are out of spec, as long as they = are *reliably* out of spec. I=92ve succeeded in twisting Linux to my ends as noted in my original = post (quoted above), but so far I haven=92t found a way to do that for = FreeBSD, short of custom modifications to the kernel and/or ntpd. Any and all suggestions will be gratefully received. Enjoy! Rick=
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