Chrony

Chrony is a time synchronization software package that implements the Network Time Protocol (NTP) and is used to maintain the accuracy of system clocks on Linux and other Unix-like systems. It offers an alternative to the traditional ntpd daemon, with a focus on fast synchronization, reliability in networks with intermittent connectivity, and suitability for virtual machines and portable devices.

Chrony consists of two main components: the chronyd daemon, which runs in the background to discipline the system clock, and the chronyc command-line utility, used to monitor and control chronyd. Chronyd communicates with time sources such as NTP servers, reference clocks, or hardware clocks, and keeps a measured offset, frequency drift, and jitter for precise control.

Chrony typically prefers continuous, gradual adjustments (slewing) over large, abrupt steps, helping maintain time stability during sleep, hibernation, or network outages. It can operate as an NTP client and, if configured, as an NTP server for other machines. It supports the NTPv4 protocol and can synchronize the local clock to multiple sources, selecting the best combination of stratum and stability.

Configuration is done via /etc/chrony/chrony.conf in most distributions. The chronyd service can be controlled with systemd, and typical commands include chronyc tracking, chronyc sources, and chronyd -q to perform one-shot queries. Chrony is widely included in Linux distributions and is also available for other Unix-like systems.