Extremely accurate system time: Chrony (not cron), PTP NIC clock and NIST (atomic clock based) time servers

[rcxb]

@E-waste

I believe it is no longer necessary to use NTP every so often to resynchronize your system clock.

That is NOT how NTP works.

Poll [How often] Do you use NTP to sync your devices time?

NTP has always done that. it uses a “hybrid phase/frequecy-lock feedback loop”[1] For a comparison between NTP and PTP, see Clock Discipline Algorithm here. If you’re using an “NTP” program that doesn’t adjust the clock (like the Windows clock internet time sync) that’s actually SNTP, not NTP proper, and you should just change your client softw…

@E-waste

Chrony is probably the most interesting Linux program there is regarding time keeping. It doesn’t poll an NTP server constantly. Instead through the wonderous power of arythmetic, will calculate drift.

Chrony isn’t unique in doing that. Since the mid-1990s, ntpd has done just that:

ntpd learns and remembers the clock drift and corrects it autonomously, even if there is no reachable server. Therefore large clock steps can be avoided while the machine is synchronized to some reference clock. In addition ntpd will maintain error estimates and statistics, and can offer NTP service for other machines.
https://www.ntp.org/ntpfaq/ntp-s-config/#611-cant-i-just-run-ntpdate