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What does clock skew detected mean?

Article ID: KB000475

UCP requires that the system clocks on all the machines in a UCP cluster be in sync or else it can start having issues checking the status of the different nodes in the cluster. To ensure that the clocks in a cluster are synced, you can use NTP to set each machine's clock.

First, on each machine in the cluster, install NTP. For example, to install NTP on an Ubuntu distribution, run:

sudo apt-get update && apt-get install ntp

On CentOS and RHEL, run:

sudo yum install ntp

On SUSE Linux, run:

sudo zypper ref && zypper install ntp

This will install NTP on each machine and start ntpd, which is a daemon which periodically syncs your machine's clock with a central server. To sync the clocks right away, on each machine run:

sudo ntpdate pool.ntp.org

You can check to see if your machine's time is in sync with its NTP servers by running:

sudo ntpq -p

The output will look similar to the following:

remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================    2 u   24   64    1   60.391  4623378   0.004
time-a.timefreq .ACTS.           1 u   23   64    1   51.849  4623377   0.004
helium.constant     2 u   22   64    1   71.946  4623379   0.004
tock.usshc.com  .GPS.            1 u   21   64    1   59.576  4623379   0.004
golem.canonical    2 u   20   64    1  145.356  4623378   0.004

The offset column shows how many milliseconds your machine's clock is out of sync with its NTP servers. Warnings are issued in the UCP UI if a time offset of more than 500 miliseconds is detected between members of the UCP cluster.