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how to emulate wrong data in shm to cheat ntpd


From: Артур Хайруллин
Subject: how to emulate wrong data in shm to cheat ntpd
Date: Tue, 2 Jun 2020 21:45:39 +0300

I am interested in opportunity to cheat ntpd by putting wrong data to shm like gpsd does. I hope it will be not so difficult for you to answer my question. I would like to thank in advance

The problem is that gps receivers i use have a strange habit to lie about the time periodically. Gpsd daemon communicates with ntpd daemon through SHM and provides data to adjust system clock. Wrong data taken from gps receivers cheat ntpd and my system for some time move forward or back on time chart for some seconds or couple of years.

I want to add to ntp.conf another ntp servers(internet) with low stratum to block that situation. But before i have to research the opportunity to cheat ntpd with gpsfake utility(i have long logs of gpspipe). I made some fixes to python scripts to make them correct and now gpsfake emulates old data. I see it in cgps utility. 

But gpsfake(as i saw yesterday) doesn't push this data to SHM. I want to know (before some code changes - if it will be necessary) if there is some mean to do that in gpsd project?

 ООО "Автодория"

Артур Хайруллин / Системный программист
ah@avtodoria.ru / +7 904 677 74 46

ООО "Автодория" 
+7 843 524 74 12 
Казань, Технопарк в сфере высоких технологий "ИТ-парк", Петербургская, 52, офис 303 
www.avtodoria.ru

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