ljylxl wrote:Also I want to try to use rdate.
If you want a simple way to sync devices then rdate is the thing to use.
I have to confess I only started off trying to set up an NTP server because I was unaware of rdate. NTP was designed to serve very accurate time to many, many clients (ie millions). It was also designed to be a better replacement for rdate (see https://en.wikipedia.org/wiki/Rdate) but it is simpler to implement than NTP and works in systems (like mine) where the main goal is to have one RTC in a system of networked computers that have no access to the internet and all need to be writing data with synchronised timestamps to allow subsequent analysis.
Having said that, I'd have stayed with NTP if the server software didn't mess with the accuracy of the RTC. The theory in our local LUG is that the drift compensation inherent in the server functionality was the cause of the problem, but no-one ever truly got to the bottom of it.
In the end, rdate was 'good enough'.