NTP

Also referred to as ntpd because it's a daemon.

There's a system called timesyncd (is it default now on Ubuntu?), but ntpd is more accurate so it's better to stick with that. I guess some people are complaining that it's not as maintained? But if that's the case, then maintain it!

See

• https://help.ubuntu.com/lts/serverguide/NTP.html
• https://www.digitalocean.com/community/tutorials/how-to-set-up-time-synchronization-on-ubuntu-16-04