May 2018

This was created and tested using CentOS 7.x

Chrony is introduced as new NTP client to replace the ntp as the default time syncing package since RHEL7, so if you configure NTP during the installation process, it just enables the chronyd service, not ntpd service.

Even when you have enabled NTP to start on boot, it will not start when chrony 
is enabled. So to enable NTP to start on boot, we have to disable the chrony service

In case you want to use NTP only, then below is the procedure to do so :

1. Disable chronyd service.
    # systemctl stop chronyd
    # systemctl disable chronyd

2. Install NTP
    # yum install ntp (probably already installed)

3. Enable and Start NTPD Service
    # systemctl enable ntpd.service
    # systemctl start ntpd.service

4. Reboot and verify.
    # systemctl status ntpd.service
    
    ● ntpd.service - Network Time Service
   Loaded: loaded (/usr/lib/systemd/system/ntpd.service; enabled; vendor preset: disabled)
   Active: active (running) since Fri 2018-05-11 08:31:47 UTC; 13min ago
 Main PID: 1486 (ntpd)
   CGroup: /system.slice/ntpd.service
           └─1486 /usr/sbin/ntpd -u ntp:ntp -g

May 11 08:31:47 eri-4e-962955 systemd[1]: Starting Network Time Service...
May 11 08:31:47 eri-4e-962955 systemd[1]: Started Network Time Service.

In the /etc/ntp.conf file you can add your own NTP server source.

  server x.x.x.x iburst

Once added, you can use the following commands to see the NTP status:

  ntpstat
  
  When you first run this you will probably see:
  
  unsynchronised
     polling server every 64 s
  
  But after a while, it should chanage (15-30 minutes normally)
  
  synchronised to NTP server (194.80.204.184) at stratum 2
     time correct to within 41 ms
     polling server every 64 s

  systemctl status ntpd.service
  
  ● ntpd.service - Network Time Service
     Loaded: loaded (/usr/lib/systemd/system/ntpd.service; enabled; vendor preset: disabled)
     Active: active (running) since Thu 2018-06-28 15:21:49 BST; 25min ago
   Main PID: 1501 (ntpd)
     CGroup: /system.slice/ntpd.service
         └─1501 /usr/sbin/ntpd -u ntp:ntp -g
  
  Jun 28 15:43:58 eri-4e-963128 ntpd[1501]: Listen normally on 17 eth4 fe80::a6bf:1ff:fe3a:54ac UDP 123
  Jun 28 15:43:58 eri-4e-963128 ntpd[1501]: Listen normally on 18 eth5 fe80::a6bf:1ff:fe3a:54ab UDP 123
  Jun 28 15:43:58 eri-4e-963128 ntpd[1501]: new interface(s) found: waking up resolver
  Jun 28 15:44:08 eri-4e-963128 ntpd[1501]: Deleting interface #18 eth5, fe80::a6bf:1ff:fe3a:54ab#1...secs
  Jun 28 15:44:08 eri-4e-963128 ntpd[1501]: Deleting interface #17 eth4, fe80::a6bf:1ff:fe3a:54ac#1...secs
  Jun 28 15:44:10 eri-4e-963128 ntpd[1501]: Listen normally on 19 eth5 fe80::a6bf:1ff:fe3a:54ab UDP 123
  Jun 28 15:44:10 eri-4e-963128 ntpd[1501]: Listen normally on 20 eth4 fe80::a6bf:1ff:fe3a:54ac UDP 123
  Jun 28 15:44:10 eri-4e-963128 ntpd[1501]: new interface(s) found: waking up resolver
  Jun 28 15:44:41 eri-4e-963128 ntpd[1501]: Deleting interface #20 eth4, fe80::a6bf:1ff:fe3a:54ac#1...secs
  Jun 28 15:44:41 eri-4e-963128 ntpd[1501]: Deleting interface #19 eth5, fe80::a6bf:1ff:fe3a:54ab#1...secs
  Hint: Some lines were ellipsized, use -l to show in full.
  

  ntpq -p
  
  This will display the timeservers found and their statistics
  
       remote           refid      st t when poll reach   delay   offset  jitter
  =============================================================================
   ttvadc02.tandbe 137.58.65.3      5 u   29   64  377    0.457  30554.8  14.013
  +www.bhay.org    85.199.214.98    2 u    6   64  377    5.135   30.351  11.382
  +time.netweaver. 85.199.214.98    2 u   34   64  377    4.581   29.606  10.153
  *194.80.204.184  .GPS.            1 u    2   64  377   14.476   30.789  13.018
  +121.35.213.162. 17.253.34.253    2 u   46   64  377    5.657   29.604  16.346

Set the TimeZone

From your servers command line enter the following:

  Date

You will see an output similar to the following:

  Fri Apr 26 06:43:49 UTC 2019

If the Time Zone needs to be changed, use the following:

cd /etc
rm localtime
ls /usr/share/zoneinfo/
ln -s /usr/share/zoneinfo/[expected_time_zone] localtime (I normally use GMT or UTC)

Use Date to re-check the current TimeZone

Original Post Herehttps://www.thegeekdiary.com/centos-rhel-7-enable-ntp-to-start-at-boot-after-fresh-install-disable-chrony/