Pablo Iranzo Gómez, Pedro Ibáñez Requena, Miguel Pérez Colino, Scott McCarty - Red Hat Enterprise Linux 9 Administration-Packt Publishing (2022) -chap 3 82 - 180
Learning about time synchronization with chrony and NTP In this section, you will understand the importance of time synchronization and how to configure the service. With connected systems, it is important to keep ab source of truth (SOT) as regards timing (think about bank accounts, incoming transfer wires, outgoing payments, and more that must be correctly timestamped and sorted. Also, consider tracing logs between users connecting, issues happening, and soon they all need to be in sync so that we can diagnose and debug between all the different systems involved. You might think that the system clock, which is defined when the system is provisioned, should be OK, but setting the system clock is not enough as the clocks tend to drift internal batteries can cause the clock to drift or to even reset, and even intense CPU activity can affect it. To keep clocks accurate, they need to be regularly synced against a reference clock that fixes the drift and tries to anticipate future drifts before the local clock is compared against the remote reference. The system clock can be synced against ab Global Positioning System (GPS) unit, for example, or more easily against other systems that have connections to more precise clocks (other GPS units, atomic clocks, and soon. NTP is an internet protocol that’s used over the User Datagram Protocol (UDP) to maintain communication between the clients and the servers. Tip NTP organizes servers by stratum. A stratum 0 device is a GPS device or anatomic clock that directly sends a signal to a server, a stratum 1 server (primary server) is connected to a stratum 0 device, a stratum 2 server is connected to stratum 1 servers, and soon. This hierarchy allows us to reduce the usage of higher-stratum servers but also keep a reliable time source for our systems. Clients connect to servers and compare the times that are received to reduce the effects of network latency. Let’s see how the NTP client works.
