Re: [chrony-users] Understand why system clock is bad even though chrony offsets look fine

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When I have systems with bizarre time issues.. I confirm that TZ is being set properly within the system..

My 0.02


On Thu, Apr 18, 2024 at 5:15 PM Abhijith Sethuraj <abhijithsethuraj4@xxxxxxxxx> wrote:

I'm noticing issues with my system clock being inaccurate by almost 50us, even though "System time" in `chronyc tracking` shows offsets in the order of ns. This was noticed by an application that tried to get current time by calling `gettimeofday()`.

Here's an entry from driftfile:
-22.346582             0.019953

Here's `chrony tracking`:
% chronyc tracking                                                  
Reference ID    : 12345 (timeserver)                      
Stratum         : 2                                                              
Ref time (UTC)  : Thu Apr 18 21:00:27 2024                                        
System time     : 0.000000017 seconds slow of NTP time                            
Last offset     : -0.000000078 seconds                                            
RMS offset      : 0.000000072 seconds                                            
Frequency       : 22.200 ppm slow                                                
Residual freq   : -0.001 ppm                                                      
Skew            : 0.019 ppm                                                      
Root delay      : 0.000073557 seconds                                            
Root dispersion : 0.000997235 seconds                                            
Update interval : 0.3 seconds                                                    
Leap status     : Normal

Here's `chronyc sourcestats`:
% chronyc sourcestats                                            
Name/IP Address            NP  NR  Span  Frequency  Freq Skew  Offset  Std Dev
timeserver                 41  19    30     -0.000      0.042     -0ns   704ns

In retrospect, I see that root delay and root dispersion are really bad above, when compared to offset. What exactly is time error here (error in time that can happen when an app tries to get current time) -- is that almost similar to "root dispersion"? Also, what recommendations do you have for monitoring chrony, so that I can catch this before it affects my app? Also, are there any config tweaks that I can try out here to help me?


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