Use time (time_t*) or clock_gettime (clockid_t,struct timespec *) if you wish for more precision, from the time.h header for the RTC time. In this tutorial, we will show you how you can check whether time synchronization is working on your Ubuntu 18.04 server. By default, Ubuntu 18.04 uses systemd’s timesyncd service for time synchronization. NTP, which stands for Network Time Protocol, is a TCP/IP protocol used for synchronizing time over a network.I believe that using an external hardware RTC and syncing it is a good solution but, is there a way to establish an internal RTC and refresh internal (or external) RTC with NTP periodically (maybe very 30 mins)? Thanks, I also assume that it drifts quite a lot but syncing with NTP every some duration would maintain a decent accuracy.Next the mechanism for updating the time over the network is NTP or Network Time Protocol. If you have followed the instructions above, you will have commented out the –systz lines in /lib/udev/hwclock-set. The first step, is to stop the RPi writing to our RTC at boot. Languages using left-hand whitespace for syntax are ridiculous.So basically persecute any automatic RPI to RTC writes with extreme vengence.

On my systems I also run hwclock -adjust from /etc/cron.daily. You need to periodically run hwclock -systohc to write the NTP time to the RTC.

Arduino manager