CentOS / RHEL 7 : Chrony V/s NTP (Differences Between ntpd and chronyd)

Chosing between Chrony and NTP

– In RHEL 7 ntpd is replaced by chronyd as the default network time protocol daemon.
– Basic configuration for synchronize time and date is stored in the file /etc/chrony.conf.
– ntpd is still included in yum repository for customers who need to run an NTP service.
– Chrony is a different implementation of the network time protocol (NTP) than the network time protocol daemon (ntpd) that is able to synchronize the system clock faster and with better accuracy than ntpd.

Benefits of Chrony include:

1. Faster synchronization requiring only minutes instead of hours to minimize the time and frequency error, which is useful on desktops or systems not running 24 hours a day.
2. Better response to rapid changes in the clock frequency, which is useful for virtual machines that have unstable clocks or for power-saving technologies that don’t keep the clock frequency constant.
3. After the initial synchronization, it never steps the clock so as not to affect applications needing system time to be monotonic.
4. Better stability when dealing with temporary asymmetric delays, for example when the link is saturated by a large download.
5. Periodic polling of servers is not required, so systems with intermittent network connections can still quickly synchronize clocks.

When to use chrony

Chrony would be considered a best match for the systems which are frequently suspended or otherwise intermittently disconnected from a network (mobile and virtual servers etc).

When to use NTP

The NTP daemon (ntpd) should be considered for systems which are normally kept permanently on. Systems which are required to use broadcast or multicast IP, or to perform authentication of packets with the Autokey protocol, should consider using ntpd.

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