Chrony
chrony is an implementation of the Network Time Protocol. It is an alternative to ntpd, a reference implementation of NTP. It runs on Unix-like operating systems and is released under the GNU GPL v2. It is the default NTP client and server in Red Hat Enterprise Linux 8 and SUSE [Linux Enterprise Server] 15, and available in many Linux distributions.
Support for Network Time Security was added in version 4.0.
Comparison with the reference implementation
In contrast to NTPsec, which is a security-focused fork of, chrony was implemented from scratch. It was designed to synchronize time even in difficult conditions such as intermittent network connections and congested networks. Some improvements in this regard include that it never steps time outside of startup, can correct for asymmetric network jitters, and can use larger clock rate adjustments on Linux to deal with a broken clock. It typically synchronizes faster and more accurately.Unlike, it supports synchronizing the system clock via hardware timestamping, improving accuracy of time synchronization between machines on a LAN - to the order of 70 nanoseconds, comparable to Precision Time Protocol. It also supports synchronization by manual input, so as to perform time correction within an isolated network.
does not implement broadcast, multicast, and anycast modes of operation. It also does not implement the insecure "autokey" authentication. It uses external programs to drive hardware time sources, unlike, which has many built-in drivers.