Chrony NTP Implementation

Chrony is a versatile implementation of the Network Time Protocol (NTP), designed as a modern, faster, and more accurate alternative to the traditional reference daemon. Developed by Miroslav Lichvar and Richard Curnow, Chrony is the default NTP client and server on RHEL, Fedora, CentOS, Ubuntu, and SUSE as of 2026. Unlike traditional implementations that can take hours to synchronize, Chrony typically synchronizes within seconds, making it ideal for virtual machines, cloud instances, and laptops. Key features include: rapid synchronization (synchronizing the system clock in seconds by using an aggressive clock discipline algorithm), accuracy (achieving better accuracy on networks with variable latency using hardware timestamping for sub-microsecond precision), offline operation (maintaining accurate time during network disconnections by calculating clock rate corrections based on drift rate), hardware timestamping (leveraging NIC PHY-level packet timestamping, eliminating software delays for sub-microsecond accuracy), selective source selection (using a modified algorithm that selects the best combination of time sources), manual time input (allowing manual time setting when no network reference is available), RTC synchronization (synchronizing the hardware real-time clock with the system clock), chronyc CLI (a rich command-line tool for monitoring synchronization status and querying sources), refclock support (supporting GPS, radio, and atomic clocks via PPS), and security (supporting NTS - Network Time Security for authenticated, encrypted NTP via TLS).