CentOS Linux: Setting timezone and synchronizing time with NTP

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:

date

You should see output like this:

Wed Jun  1 10:33:29 PDT 2011

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@serve3 ~]# 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:

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

ntpd

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 127.127.1.0     # local clock
#fudge  127.127.1.0 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

27 thoughts on “CentOS Linux: Setting timezone and synchronizing time with NTP

  1. Hi Auther,
    I have installed NTPD and service is running as daemon. The service is syncing time properly from NTP server.

    My question is, does NTPD (NTP Client) also syncs timezone from NTP server if it is different at Client over NTP Server ?

  2. Linex server selected time zone is Ashia Kolkatta but it gives IST+5.30 timestamp. how to get rid of this additional +5.30 offset to get correct IST time.

  3. it shows time equals current time +5.30. and error no servers can be useed, exiting. ntpq -p shows server synced to gps server.

    • What command did you run? Did you run ntpdate pool.ntp.org? Try shutting down the ntp service before running ntpdate.

  4. I have a situation which my apps in client needs to set as GMT 0, so I set to Aftica/Casablanca (no DST). My time zone is GMT +8. But, even I set to Africa/Casablanca, I still want it to be the same time as GMT +8. I have setup an intermediate server that will synchronize with my ntp server. the question is how I would do it to synchronize with ntp server? I’ve tried to change the date and ntpd died. is there any ways for ntp to synchronized without reset the time based on timezone set at the client?

    • That doesn’t make any sense. You have me thoroughly confused.

      Why set it to Casablanca if you want GMT? Set it to GMT or UTC which is the same thing.

  5. When i set the time for cairo egypt the clock keeps changing as the gov decided not to go on summer time this year.
    I tried to apply the NTP service to update but didn’t succeed to get the correct time.
    Any advice what to do?
    Also is there a way to set the clock manually & prevent it from updating??

    • Do a yum update because new timezone data is released all the time and yum will update it on your system.

      Generally on servers you set the hardware clock to UTC and then you can set your own timezone in the OS if you are the only user on the system. If the system is shared with users from around the world people stick to UTC.

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