There are a couple tools you can use to validate whether ntp is functioning normally.
First is ntpstat, which will show you which ntp server the device is currently synchronized with:
ntpstat synchronised to NTP server (188.8.131.52) at stratum 3 time correct to within 1945 ms polling server every 1024 s
In the above we can see that this server is actually in sync, but only in sync within 1945ms which is about 2 seconds. This seems a bit long to me and since we were getting an alert I decided to see if the server was actually accessible.
After a ping, it looks like I was unable to access it.
Tried manually syncging with ntpdate -q 184.108.40.206 and it was unable to perform the task
ntpdate -q 220.127.116.11 server 18.104.22.168, stratum 0, offset 0.000000, delay 0.00000 12 Feb 11:22:12 ntpdate: no server suitable for synchronization found
I restarted ntpd:
service ntpd restart
It looked like it had a new set of peers, but was still unsynchronized:
# ntpq -p remote refid st t when poll reach delay offset jitter ============================================================================== penguin.hopcoun 22.214.171.124 2 u 44 64 1 10.000 0.369 0.000 ks4001083.ip-19 126.96.36.199 2 u 43 64 1 13.813 0.007 0.000 time1.srv.ualbe .GPS. 1 u 44 64 1 147.417 -48.701 0.000 # ntpstat unsynchronised time server re-starting polling server every 64 s
After a while though it eventually synched and everything was fine
# ntpstat synchronised to NTP server (188.8.131.52) at stratum 2 time correct to within 60 ms polling server every 256 s
In redhat you can also configure additional logging by adding the -l $dir in /etc/sysconfig/ntpd and restarting the service.