[chrony-users] Requesting some insight regarding preferred servers and RTCSYNC/RTCFILE

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Hi all,

I have recently taken over the development of an embedded project. It runs a custom Linux build on a Colibri T30 system, including Chrony.

The device has an RTC on-board and is also connected to a LAN with multiple of the device. However, the LAN is not necessarily connected to internet.

The main purpose of the device is monitoring and logging, applying some statistical analysis on data and wrapping it into accessible data formats.. For this purpose, somewhat accurate time (a few minutes off max) is necessary. The devices are placed in hard-to-reach locations and should be able work autonomously for years at a time. The devices can reboot on a moments notice with unknown intervals, at least once every 48 hours.

The device with its current settings seems to work as expected but I have my doubts that the device is really working as expected or if it just seems to be close enough. I have two main concerns I would like to have straightened out that I could not clearly do away with by reading the manual and some installation guides. The current configuration file is as follows:

refclock SOCK /var/run/chrony.DUM1.sock refid DUM1
refclock SOCK /var/run/chrony.RTC.sock refid RTCC delay 1e-3

pool 0.nl.pool.ntp.org iburst
pool 1.nl.pool.ntp.org iburst
pool 2.nl.pool.ntp.org iburst
pool 3.nl.pool.ntp.org iburst

allow all
local stratum 10
makestep 300 -1
logdir /var/log/chrony
log measurements statistics tracking refclocks rtc
logchange 60
pidfile /var/run/chronyd.pid

My first concern lies with the RTC. In the current configuration, neither RTCSYNC nor RTCFILE are defined. Does Chrony still correct the system time while it's running? Or only at boot? Or never? 

Secondly, a new feature needs to be added to the system. Other than syncing to the RTC or other devices on the network, an NTP server needs to be added that has precedence over any other source. I saw in the manual that the parameter 'prefer' can be added to the server, causing Chrony to prefer that server. However, is there a scenario where Chrony still picks a non-preferred source? Is there a degree of 'quality' that the preferred server needs to have in order to have guaranteed precedence?

I understand that the current configuration is not exactly 'as it should be'. The development of this embedded system was really messy and the engineer who made this is no longer working for the company. He left no documentation behind on this part, so I can only guess what exactly the reasons were for setting stratum to 10 or the makestep to -1. But I don't want to change anything that is not necessary because failure of logging is unacceptable. 

If anyone can address my concerns and/or explain why this configuration works, I would be very grateful.

kind regards,

Martin Janse

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