Re: chrony not switching to stratum 10 after loss of references

The  local time is the time on your compter. So you want to set the time on
your computer to itself. Not a very useful thing to do. There is not some
maging clock. Chrony will keep reporting its own time as long as its estimate
of the error in your local time is small enoght. Why not? It has spent much
time getting the local erros down, but fitting to to tfind the offset and the
rate of the local clock. So many people decide to test by sutting off all
imput, and expectingchrony to do something weid to allevate the problem. Trust
that the designers of chrony have thought about what to do in that case and to
try to delive the best time they can, even in that situation. (and using the
local clock to set itself is almost never the best solution, since that throws
awy all of the work it has done fguring out what the best parameters are to
keep the local clock on track for a long time).

William G. Unruh __| Canadian Institute for|____ Tel: +1(604)822-3273
Physics&Astronomy _|___ Advanced Research _|____ Fax: +1(604)822-5324
UBC, Vancouver,BC _|_ Program in Cosmology |____ [email protected]
Canada V6T 1Z1 ____|____ and Gravity ______|_    theory.physics.ubc.ca/

On Wed, 14 Jun 2023, Charbonneau, André wrote:

> [CAUTION: Non-UBC Email]
> 
> Hi,
> 
>  
> 
> I’m having a problem with a system configured as a stratum 1 NTP server, running chrony, and I can’t
> seem to be able to figure out what is happening and what might be the root cause of the problem.
> 
> (details about the setup are at the end of this message)
> 
>  
> 
>  
> 
> Basically, my stratum 1 servers takes a 1PPS and NMEA timecode on a serial port.  It also runs gpsd. 
> I’ve configured the SHM references as such in /etc/chrony.conf:
> 
>  
> 
> # Configure NMEA + 1PPS via shared memory:
> 
> refclock SHM 0 refid NMEA precision 1e-1 offset 0.000109
> 
> refclock SHM 1 refid PPS offset 0.0 precision 1e-7
> 
> <… snip …>
> 
> local stratum 10
> 
>  
> 
> With this configuration, chrony is happy, sees the 2 signals (e.g., reach of 377 on each) and serves
> time as a stratum 1 server.  All good so far.
> 
>  
> 
>  
> 
>  
> 
> But then I intentionally stop the 1PPS and timecode signals to simulate a failure of the upstream
> reference.  Because of the “local stratum 10”, I was expecting chrony to switch stratum 10
> automatically when the reach value reaches 0 on those 2 references, but this is definitely not what
> I’m seeing.
> 
>  
> 
> Instead, it seems like chrony continues to be a stratum 1, long after the reference signal have been
> terminated. 
> 
> For example, the chrony sources and tracking command output below was taken approx. 1 hour after
> termination of 1PPS and NMEA signal:
> 
>  
> 
> $ sudo date; sudo chronyc sources; sudo chronyc tracking
> 
> Wed Jun 14 08:23:00 PM UTC 2023
> 
> MS Name/IP address         Stratum Poll Reach LastRx Last sample              
> 
> ===============================================================================
> 
> #? NMEA                          0   4     0   57m    -93us[  -93us] +/-  100ms
> 
> #? PPS                           0   4     0   57m    +98ns[ +346ns] +/-  101ns
> 
> Reference ID    : 50505300 (PPS)
> 
> Stratum         : 1
> 
> Ref time (UTC)  : Wed Jun 14 19:25:50 2023
> 
> System time     : 0.000000041 seconds fast of NTP time
> 
> Last offset     : +0.000000256 seconds
> 
> RMS offset      : 0.000000151 seconds
> 
> Frequency       : 12.835 ppm fast
> 
> Residual freq   : +0.006 ppm
> 
> Skew            : 0.008 ppm
> 
> Root delay      : 0.000000001 seconds
> 
> Root dispersion : 0.003475379 seconds
> 
> Update interval : 16.0 seconds
> 
> Leap status     : Normal
> 
>  
> 
> I’ve also confirmed that it still happily serves time at stratum 1 level if I query it from another
> system (using ntpdate tool for example from another system). 
> 
>  
> 
> Is this normal and expected?  I was expecting chrony to fallback to stratum 10 but this is not what is
> happening.
> 
>  
> 
> There is probably something obvious I’m missing in my chrony.conf file to implement the desired
> behavior but I’m not able to figure it out.
> 
>  
> 
> Anyone else experienced this before?
> 
>  
> 
>  
> 
> System and setup info:
> 
>  
> 
> HP EliteDesk 800 G2 SFF
> 
> chrony version 4.3
> 
> gpsd 3.23.1-1.el9
> 
> AlmaLinux release 9.2 (Turquoise Kodkod)
> 
> Linux 5.14.0-284.11.1.el9_2.x86_64 #1 SMP PREEMPT_DYNAMIC Tue May 9 05:49:00 EDT 2023 x86_64 x86_64
> x86_64 GNU/Linux
> 
>  
> 
> chrony.conf:
> 
>  
> 
> refclock SHM 0 refid NMEA precision 1e-1 offset 0.000109
> 
> refclock SHM 1 refid PPS offset 0.0 precision 1e-7
> 
> driftfile /var/lib/chrony/drift
> 
> leapsecmode system
> 
> makestep 1.0 3
> 
> rtcsync
> 
> hwtimestamp *
> 
> minsources 1
> 
> allow ***.***.0.0/16
> 
> local stratum 10
> 
> logdir /var/log/chrony
> 
> log measurements statistics tracking refclocks tempcomp
> 
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> Any information or insights about this would be much appreciated.
> 
>  
> 
> Thanks,
> 
>   Andre
> 
>  
> 
>  
> 
> --
> 
> Andre Charbonneau
> 
>  
> 
> Frequency & Time
> 
> Metrology Research Centre
> 
> National Research Council Canada / Government of Canada
> 
> [email protected] / 613-993-3129
> 
>  
> 
> Fréquence et temps
> 
> Centre de recherche en métrologie
> 
> Conseil national de recherches Canada / Gouvernement du Canada
> 
> [email protected] / 613-993-3129
> 
>  
> 
> 
>