[chrony-users] chrony not switching to stratum 10 after loss of referenc

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

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

andre.charbonneau@xxxxxxxxxxxxxx / 613-993-3129

Fréquence et temps

Centre de recherche en métrologie

Conseil national de recherches Canada / Gouvernement du Canada

andre.charbonneau@xxxxxxxxxxxxxx / 613-993-3129