Clock not in sync

Latest response

Hi All,

We are facing an issue of clock sync between our rhel 7.6 nodes configured in vmware 6.5.
We have checked the same with enabling/disabling Chrony,NTP services and also by setting up local time.
We still are getting time difference which is gradually increasing and when the load of boxes increases the difference increases rapidly which is impacting our performance testing.
Kindly suggest resolution. :)

Responses

Did you check https://www.redhat.com/en/blog/avoiding-clock-drift-vms and https://access.redhat.com/solutions/278273?

Hello Rohit Verma,

Thanks for posting here. Along with what Siem Korteweg mentioned above, make sure to properly set up either ntp or chrony Note, that is a long read, but worth the effort. NOTE: ntp will no longer be in RHEL 8, but you are using RHEL 7, so that is just an FYI.

Rohit Verma

Make sure to set up a server/client ntp (chrony) scenario. make primary servers pointing (if possible) to valid stratum 1 servers. I don't know your environment. In principle, have a couple of systems on your network be stratum 2 servers (they point to stratum 1 servers). If you have your own stratum 1 server, even better. Point the clients of your Linux servers to your primary ntp/chrony servers that are pointing to stratum 1 servers (not everything should point to a stratum 1 server, generally). I'd read up on establishing NTP and it's overall principles, which relate in principle to Chrony. Do not make virtual servers your primary ntp servers. (see Siam Korteweg's post)

Regards

RJ

All,

Bare in mind, it is bad practise to build a ntp server on a Virtual Machine on any hypervisor, another reference: http://support.ntp.org/bin/view/Support/KnownOsIssues#Section_9.2.2.

Regards,

Jan Gerrit

Anyone coming to this page, keep in mind the bit Jan Gerrit Kootstra mentioned (I kinda mentioned it, but he is clearer here).

Regards

RJ

Did that . I am getting average 11ms delay between 2 nodes.

Hi Rohit,

11 ms delay between 2 nodes?!? What time do you measure?

An 11 ms delay between 2 VMs at the ntp servers or something else?

What some of these documents our fellow members point you too are hinting too, do not mix ntp time synchronization and VMware guest/host synchronization. Turn the VMware type of time synchronization off, even VMware is recommending it, but I cannot find the Knowledge Base article right now.

Regards,

Jan Gerrit

I'm reminded to be clearer, for good cause. It's recommended not to use a virtual system as an ntp server. Examine these instructions for the use of chronyd, and also here are some basic best practices for ntp which was last updated in 2016, and contains time principles from an NTP perspective (chronyd is discussed a little there, but many of the principles in NTP are still relevant).

This link here is specific to configuring NTP using the chrony suite). ***and as I type this, I see this is the identical link to the chronyd documentation I posted earlier)