NTP, CHRONY, OPEN-vm-tools... Best Practices for time management in RHEL/CentOS 7?


I am (finally) working on creating a CentOS 7 VMware (ESXi) Template - currently ESXi/vCenter 5.5+.

Past usage of time management within a guest has varied and we have utilized KB 1006427 (https://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1006427) however it has not been updated for RHEL 7.

My Google-fu is failing me.

I am utilizing open-vm-tools and just looking for best practices for time management within the Linux guest.

  • 1
    Hi Charlie, in the link you posted in your entry you have your answer: "NTP Recommendations: VMware recommends using NTP instead of VMware Tools periodic time synchronization. NTP is an industry standard and ensures accurate timekeeping in your guest. It may be necessary to open the firewall (UDP 123) to allow NTP traffic." See RedHat website link for further information how to set it up.
    – Paul
    May 27, 2016 at 14:17

2 Answers 2


I understood that if your VMs get switched on and off often (as in auto-scaling) chronyd is the better service:


If your computer is connected to the Internet only for few minutes at a time, the network connection is often congested, you turn your computer off or suspend it frequently, the clock is not very stable (e.g. there are rapid changes in the temperature or it’s a virtual machine), or you want to use NTP on an isolated network with no hardware reference clocks in sight, chrony will probably work much better for you.

If always on, then ntpd, as Paul mentions.

  • Thanks for the quick replay Jay, Paul.I'll stick with NTP as opposed to Chrony for my situation. Ideally VMware updates their KB to include RHEL7/CentOS7.
    – Charlie O
    May 27, 2016 at 14:43

The difference between RHEL/CentOS 6.x and 7.x from the perspective of NTP should be insignificant; follow the best practices guide for 6.x. Note that the KB article you linked to suggests only 3 time sources; 4 or more is preferred.

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