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Time synchronization with Network Time Protocol: Basic concept

Publication Date: 05/24/2022

1 Environment

This document applies to the following products and product versions:

  • SUSE Linux Enterprise Server 15 SP3, 15 SP2, 15 SP1, 15 GA

  • SUSE Linux Enterprise Server for SAP Applications 15 SP3, 15 SP2, 15 SP1, 15 GA

  • SUSE Linux Enterprise High Availability Extension 15 SP3, 15 SP2, 15 SP1, 15 GA

  • SUSE Linux Enterprise High Performance Computing 15 SP3, 15 SP2, 15 SP1, 15 GA

  • SUSE Linux Enterprise Desktop 15 SP3, 15 SP2, 15 SP1, 15 GA

  • SUSE Linux Enterprise Real Time 15 SP3, 15 SP2, 15 SP1, 15 GA

2 Introduction

Maintaining an exact and synchronized system time on the computer is a requirement for team work. For example, planning and calendaring applications rely on it to track time correctly and notify users about appointments on time. For clustered applications, individual host machines often require synchronized system time for mutual communication.

The built-in hardware clock is not a reliable time source and manual correction of the system time might cause malfunction of critical applications. That is why the Network Time Protocol (NTP) is designed to synchronize the system time over the network. Its goal is to maintain the absolute time, and use it to synchronize the system time of all machines within a network.

3 How it works

When the NTP service is properly configured, it continuously queries and adjusts the system time with reliable time servers. Typically, home computers and other devices connected to the internet are configured to query a public time server on the internet.

Individual devices querying a public time server
Figure 1: Individual devices querying a public time server

Conversely, desktop computers and servers that reside inside a corporate subnet are configured to query a dedicated time server within the local network. The time server itself synchronizes its time with a public time server.

Multiple hosts querying an internal time server
Figure 2: Multiple hosts querying an internal time server

4 Implementation

Since SUSE Linux Enterprise Server 15, chrony is the default implementation of NTP. chrony includes two parts:

  • chronyd is a systemd service that can be started at boot time.

  • chronyc is a command line interface program to monitor the performance of chronyd, and to change various operating parameters at runtime.

5 Benefits

Using NTP to maintain the exact time has the following benefits:

  • People can rely on their clocks when following a planned schedule, and applications can trigger scheduled actions accurately.

  • Using an internal time server to maintain the exact system time on multiple machines within the same network allows for a more secure setup with restricted access to the internet.