NTP
"Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks. In operation since before 1985, NTP is one of the oldest Internet protocols in current use." - https://en.wikipedia.org/wiki/Network_Time_Protocol
Links
- RFC 5905: Network Time Protocol Version 4: Protocol and Algorithms Specification
- Understanding and mitigating NTP-based DDoS attacks
- Google Public NTP: Leap Smear
- Five different ways to handle leap seconds with NTP
- The Unix leap second mess
- ntp.org FAQ: What happens during a Leap Second?
- The Raspberry Pi as a Stratum-1 NTP Server
- NTP vs PTP: Network Timing Smackdown!
ntp daemon in systemd
Systemd has its own time and date tools that replace classic linux tools like ntpd. See systemd-timesyncd and timedatectl. systemd-timesyncd refuses to start if the ntp package is installed.