synchronise time using ntpd and timesyncd

Imagine that you have many servers. It's important to have synchronized time between our servers - at least the log files should have same time in order to find out the correct sequence of the processes. We can use the following tools for time synchronization

• ntpd - powerfull Network Time Protocol Daemon. Full implementation of  NTP protocol
• systemd-timesyncd - it is lightweight daemon for synchronizing the system clock. This client implements an SNTP.  if we  have ntpd daemon we can use ntpdc - utility program used to monitor NTP daemo (now it's deprecated and we use ntpq).  If we have systemd-timesyncd we can use  timedatectl - it has very beautiful configurations and controls the system time/date very well.
• chrony is also full implementation of NTP. it has really great performance because It quickly detects sudden time changes like ntpd.   
• OpenNTPD - It's part of the Open BSD project that also implements NTP protocol.
  

There are another implementations too but know let's talk for about ntpd and timedatectl.

 How to Configure ntpd

• Install and enable ntpd for CentOS:

yum install ntpd
systemctl enable ntpd
firewall-cmd --add-service=ntp --permanent

• Install and enable ntpd for Debian:

apt-get install ntpd
apt-get install ntpdate

• Add pools in  /etc/ntp.conf  server configuration

server 0.[YOUR_POOLl]
server 1.[YOUR_POOLl]

• Add local clock in  /etc/ntp.conf  server configuration.  For example, we can add local clock as a stratum 10  server or we  can set up to stratum 15 - so that it will never be used unless internet access is lost.

server  127.127.1.0 
fudge   127.127.1.0 stratum 10

• Add pool adress in /etc/ntp.conf client configuration

server  X.X.X.X

• Force update time, we can create crontab too (optional)

ntpdate -u X.X.X.X

• Start ntpd service for CentOS:

systemctl start ntpd

• Start ntpd service for Debian:

service ntp start  or systemctl start ntp

Let's check if everything works well and print all the peers of the servers

[vq@centos etc]# ntpq -p
 remote   refid  st t when poll reach delay  offset jitter
===========================================================
*LOCAL(0) .LOCL. 10 l 40  64   17     0.000  0.000  0.000

 How to Configure timesyncd

Because of we have installed ntpd we can't use systemd-timesyncd. Even if you try to use systemd-timesyncd service you will have the follolwing error:

vq@debian:/var/log# systemctl status 

systemd-timesyncd.service
● systemd-timesyncd.service - Network Time Synchronization
   Loaded: loaded 
(/lib/systemd/system/systemd-timesyncd.service;
 enabled; vendor preset: enabled)
  Drop-In: /lib/systemd/system/systemd-timesyncd.service.d
           └─disable-with-time-daemon.conf
   Active: inactive (dead)
Condition: start condition failed at 
Fri 2018-07-27 13:31:23 +04; 35s ago
           └─ ConditionFileIsExecutable=
!/usr/sbin/ntpd was not met
     Docs: man:systemd-timesyncd.service(8)

So we should remove ntpd if we want to use  timesyncd and timedatectl. You can find  timesyncd configuration to the following URL:

/etc/systemd/timesyncd.conf

[Time]
NTP= ${URLS}
FallbackNTP=${URLS}
#RootDistanceMaxSec=5
#PollIntervalMinSec=32
#PollIntervalMaxSec=2048

• check if NTP synchronization is enabled 

 
vq@debian:/etc# timedatectl
      Local time: Fri 2018-07-27 13:27:36 +04
  Universal time: Fri 2018-07-27 09:27:36 UTC
        RTC time: Fri 2018-07-27 09:46:02
       Time zone: Asia/Tbilisi (+04, +0400)
 Network time on: YES
NTP synchronized: YES
 RTC in local TZ: YES