RE: RHEL 7 and Chrony

From: Herring, David <>
Date: Wed, 15 Feb 2017 14:47:30 +0000
Message-ID: <>

In case anyone is interested I received a pretty good answer from Oracle support about this.

I think it boils down to the fact that the chrony service at times has been seen to not correct the time immediately or within acceptable parameters and this causes issues with RAC and multiple instances that require heavily on time synchronization.

If there is a discrepancy reported from the NTP/GPS server to chrony it speeds up or slows down the system clock, whereas ntp client will make the change right away depending on the amount and whether or not slewing option is used (which is recommended, btw)

For instance, say there was a 5 minute discrepancy, between the system clock and the NTP/GPS reported time.

From my understanding, chrony would speed up the system clock until that 5min gap was gone. That could take a significant amount of time depending on threshold the application has. Now my understanding of ntp client is that it will automatically increase the time immediately (depending on slewing option) (+1min, +1min, etc.) until it is synchronized with the server.

Doc ID 2068875.1 :
"The often misconception is that the chrony service is setting the time to the one given by the NTP server. This is incorrect - what actually happens is that based on the answer from the NTP server, chrony just tells the system clock to go faster or slower. For this reason, sometimes even though the time is wrong and the NTP server is working, the time does not get corrected immediately."

... unfortunately it appears that's the way(support for ntp client) it is going to be for the foreseeable future. Unless of course customer demand and/or necessity dictate otherwise.



From: Herring, David
Sent: Tuesday, February 07, 2017 2:06 PM To:
Subject: RHEL 7 and Chrony


Does anyone have insight as to why Oracle still relies on NTP even though Redhat has moved on with Chrony as of v7? Various "cluvfy" commands still assume the use of NTP and give warnings without it (not a huge deal) but we found on RHEL 7.x with after host reboots the CRS won't come back up due to issues with NTP not being configured. For now our 7.x install instructions require NTP but our Linux team isn't thrilled about the one-off requirement for NTP.



Received on Wed Feb 15 2017 - 15:47:30 CET

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