Learn how to set the correct timezone and synchronize time with NTP servers on your CentOS box.

Setting the timezone
Setting the timezone on CentOS or Redhat Enterprise Linux (RHEL) is easy.

Login as root either locally or remotely via SSH.

See what the current timezone is:

You should see output like this:

Wed Jun 1 10:33:29 PDT 2017
To change the timezone first look at what timezones are available by running the following command on the command line interface:

ls /usr/share/zoneinfo/
You should see a listing like this:

[root@567ss.com ~]# ls /usr/share/zoneinfo
Africa Australia Cuba Etc GMT0 Iceland Japan MST Poland right Universal Zulu
America Brazil EET Europe GMT-0 Indian Kwajalein MST7MDT Portugal ROC US
Antarctica Canada Egypt Factory GMT+0 Iran Libya Navajo posix ROK UTC
Arctic CET Eire GB Greenwich iso3166.tab MET NZ posixrules Singapore WET
Asia Chile EST GB-Eire Hongkong Israel Mexico NZ-CHAT PRC Turkey W-SU
Atlantic CST6CDT EST5EDT GMT HST Jamaica Mideast Pacific PST8PDT UCT zone.tab
Then simply delete the current timezone:

rm /etc/localtime
And replace it with a symbolic link to the new timezone from /usr/share/zoneinfo. For example if your chosen zone is Pacific time:

ln –s /usr/share/zoneinfo/PST8PDT /etc/localtime
Synchronizing time with NTP server
Network Time Protocol (NTP) is a standard way of synchronizing computer clocks across a network. Using NTP you can keep your server’s clock synchronized with super accurate atomic clocks located around the world. Computer clocks tend to “drift” so regularly synchronizing them with NTP servers helps keep them accurate.

The first step is to make sure you have the ntp program installed. Do a:

which ntpdate
If its not available type:

yum install ntp
Once ntp is installed synchronize your computer clock with:

To use this pool zone, add the following to your ntp.conf file:

server 0.us.pool.ntp.org
server 1.us.pool.ntp.org
server 2.us.pool.ntp.org
server 3.us.pool.ntp.org

ntpdate 0.us.pool.ntp.org
You are not limited to the above server. There are numerous NTP servers around the world. You can find a complete list at ntp.org.

Also keep in mind that ntp only affects the system time. The hardware clock on your server will not reflect that. So you want to set it as well so that the correct time is maintained after reboot:

hwclock –systohc
To keep your server clock automatically synchronized you can run the ntpd daemon which is installed as part of the ntp package.

Edit the /etc/ntp.conf file to comment out the following lines:

#server # local clock
#fudge stratum 10
The above two lines can sometimes prevent ntpd from properly synchronizing your clock. They are already commented out by default on CentOS/RHEL 6. But on 5.x you have to comment them out manually.

Finally type the following two commands to start the daemon and make it run automatically at boot up:

service ntpd start
chkconfig ntpd on