Config:

/etc/ntp.conf

Commands:

ntptrace                                                   #Show sync stats
watch -n1 -d ntptrace                                      #Show continiously sync stats
ntpq -p                                                    #NTP query program
ntpq -pn                                                   #NTP query program. showing IP instead of DNS name
ntpdate -s time.server.com && /sbin/hwclock --systohc
ntpdate -b time.server.com                                 #force sync - ntpd has to been switched off during sync!

“offset”:

Shows timedifference between reference time (timeserver) and system time (OS)

“jitter”:

Indicates the magnitude of the fluctuations between individual time comparisons

(worst case) Example:

[root@testsap ~]# ntpq -pn
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*10.200.1.11     192.168.47.125    4 u  652 1024  377    0.545    0.944   1.939
+10.200.1.12     192.168.47.126    5 u  705 1024  377    0.469    1.579   3.187
+10.200.1.13     192.168.47.12     6 u  592 1024  377    0.342    2.999  22.494

Check from a Linux-Client:

vi /etc/ntp.conf          #Select NTP-server you want to check
date -s "1974-01-04"
date --set="2 OCT 2006 18:00:00"
date +%T -s "20:46:05"
service ntpd restart
systemctl restart ntpd.service
date
timedatectl set-timezone Europe/Berlin
timedatectl 
dpkg-reconfigure tzdata