Setting multiple NTP servers in /etc/systemd/timesyncd.conf

Solution 1:

this is by design of timesyncd. TL;DR it is only capable to use one at a time.

Details: If you look very hard at the timesyncd man page you will see that is say in the section about multiple NTP servers:

... until one is found that responds ...

If you dig deeper you'll find issues like timesyncd: talks only to one NTP server at a time and systemd-timesyncd manual should explain it uses SNTP, not NTP.

So it will take the first one out of the NTP= list that works, and if all in there fail try the list in FallbackNTP=.

If you want real cross server checks for better sync you should take a look at NTPd (<18.04) / Chrony (>=18.04) quoting the systemd issue on that:

Yeah, systemd-timesyncd implements SNTP, not NTP, hence multi-server support is out of focus. If you want a full NTP implementation, please use ntpd or chrony.