Re: [chrony-users] Syncing time as with a single request

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> On Jan 28, 2020, at 2:35 AM, Miroslav Lichvar <mlichvar@xxxxxxxxxx> wrote:
> On Tue, Jan 28, 2020 at 04:11:49AM +0000, Gustav Krantz wrote:
>> Would it be possible to do the initial sync with a single request per server? If so how would this be done and what would the drawback be?
> The current development code in git supports a single-sample
> selection/update mode, enabled by setting maxsample to 1, but it's
> meant to be used only in the "ntpdate" mode (-q/-Q option) as it
> doesn't adjust the frequency of the clock. You could use it for the
> initial correction before normally starting chronyd.
> # chronyd -q 'pool maxsamples 1 iburst'

I have been testing this new "maxsamples 1" feature with the latest chrony-master.tar.gz snapshot of 2020-02-19.

Works very nicely.  Our project first does a quick foreground "chronyd -q ..." step (historical from sntp/ntpdate days) and then followed by a background chronyd .

With "maxsamples 1", our boot times are 4-6 seconds faster.

Using, the step is performed in about 230 ms.  (versus 4.4 seconds before)
pbx4 ~ # time chronyd -q -t 8 "server maxsamples 1 iburst"
2020-03-01T21:31:53Z Initial frequency -17.927 ppm
2020-03-01T21:31:53Z System clock wrong by -0.000330 seconds (step)
2020-03-01T21:31:53Z chronyd exiting

real	0m0.229s
user	0m0.006s
sys	0m0.005s

While testing, a '-t 8' is needed since DNS errors/misconfigurations can cause "chronyd -q ..." to hang, seemingly forever.

Example, using a typo .con instead of .com ... Control-C'ed to quit:
pbx4 ~ # time chronyd -q "server time.cloudflare.con maxsamples 1 iburst"
2020-03-01T21:34:23Z Initial frequency -17.927 ppm
^C2020-03-01T21:41:07Z chronyd exiting

real	6m43.632s
user	0m0.003s
sys	0m0.010s

Adding the '-t 8' guards against those special DNS issues, without it a box could hang at startup.  Example, same typo with a '-t 8':
pbx4 ~ # time chronyd -q -t 8 "server time.cloudflare.con maxsamples 1 iburst"
2020-03-01T21:41:38Z Initial frequency -17.927 ppm
2020-03-01T21:41:46Z chronyd exiting

real	0m8.014s
user	0m0.002s
sys	0m0.009s


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