This mini how-to will show you how to change the timezone in RHEL derived servers.

Configuration in RHEL/CENTOS/ORACLE LINUX release 6.

  1. List time zones 
    ls /usr/share/zoneinfo
  2. Change the Time Zone. In the graphical mode you can set up the time zone using system-config-date command. 
    sudo mv /etc/localtime /etc/localtime.bkp 
sudo ln -s /usr/share/zoneinfo/America/Asuncion /etc/localtime
sudo vim /etc/sysconfig/clock

    [sergio@localhost ~]$ sudo cat /etc/sysconfig/clock
# The time zone of the system is defined by the contents of /etc/localtime.
# This file is only for evaluation by system-config-date, do not rely on its
# contents elsewhere.
ZONE="America/Asuncion"
  3. View when clock will change forward or backward 
    [sergio@localhost ~]$ zdump -v /etc/localtime | grep 2018
/etc/localtime  Sun Mar 25 02:59:59 2018 UTC = Sat Mar 24 23:59:59 2018 PYST isdst=1 gmtoff=-10800
/etc/localtime  Sun Mar 25 03:00:00 2018 UTC = Sat Mar 24 23:00:00 2018 PYT isdst=0 gmtoff=-14400
/etc/localtime  Sun Oct  7 03:59:59 2018 UTC = Sat Oct  6 23:59:59 2018 PYT isdst=0 gmtoff=-14400
/etc/localtime  Sun Oct  7 04:00:00 2018 UTC = Sun Oct  7 01:00:00 2018 PYST isdst=1 gmtoff=-10800
  4. If you need to use a particular Timezone in your environment you can easily use the TZ variable and set you time zone. 
    [sergio@localhost ~]$ date; export TZ="America/Argentina/Ushuaia"
Wed Sep 27 18:19:51 PYT 2017
[sergio@localhost ~]$ date
Wed Sep 27 19:19:55 ART 2017

Configuration in RHEL/CENTOS/ORACLE LINUX release 7.

  1. You can list the Time zone using timedatectl command as follow 
    timedatectl list-timezones

    Or search the Timezone interactibly with the tzselect command

  2. Change the Time zone. 
    timedatectl set-timezone America/Asuncion
  3. Verify the changes and the dates when clock will change. 
    [root@loadbalancer ~]# timedatectl
   Local time: mié 2017-09-27 19:22:59 -04
  Universal time: mié 2017-09-27 23:22:59 UTC
     RTC time: mié 2017-09-27 23:22:58
    Time zone: America/Asuncion (-04, -0400)
  NTP enabled: n/a
NTP synchronized: no
 RTC in local TZ: no
   DST active: no
 Last DST change: DST ended at
               sáb 2017-03-25 23:59:59 -03
               sáb 2017-03-25 23:00:00 -04
 Next DST change: DST begins (the clock jumps one hour forward) at
               sáb 2017-09-30 23:59:59 -04
               dom 2017-10-01 01:00:00 -03
  4. You can use zdump to view when the clock will change. 
    [root@loadbalancer ~]# zdump -v /etc/localtime | grep 2018
zdump: atención: zona "/etc/localtime" abreviatura "-04" no tiene caracteres alfabéticos al comienzo
/etc/localtime  Sun Mar 25 02:59:59 2018 UTC = Sat Mar 24 23:59:59 2018 -03 isdst=1 gmtoff=-10800
/etc/localtime  Sun Mar 25 03:00:00 2018 UTC = Sat Mar 24 23:00:00 2018 -04 isdst=0 gmtoff=-14400
/etc/localtime  Sun Oct  7 03:59:59 2018 UTC = Sat Oct  6 23:59:59 2018 -04 isdst=0 gmtoff=-14400
/etc/localtime  Sun Oct  7 04:00:00 2018 UTC = Sun Oct  7 01:00:00 2018 -03 isdst=1 gmtoff=-10800
  5. If you need to use a particular Time zone in your environment you can easily use the TZ variable and set you time zone. 
    [sergio@localhost ~]$ date; export TZ="America/Argentina/Ushuaia"
Wed Sep 27 18:19:51 PYT 2017
[sergio@localhost ~]$ date
Wed Sep 27 19:19:55 ART 2017

Sometimes the goverment change the Daylight Saving Time or DST. To achieve this accomplish you can compile a new time zone using the zic command. First download the IANA TIME ZONE DATABASE, this is because it contains the code and data that represent the history of localtime for many locations.

wget https://www.iana.org/time-zones/repository/releases/tzdata2017b.tar.gz

After extract the data you can use it as reference for your new file. In my case this is only dummy file.

vim test.zic

#Rule  NAME  FROM  TO    TYPE  IN   ON       AT    SAVE  LETTER/S
Rule  test    2017  only  -     Apr  Sun>=1  0:00   1:00  S
Rule  test    2017  only  -     Oct  Sun>=1  0:00   0  -
#Zone  NAME                GMTOFF  RULES/SAVE  FORMAT  [UNTIL]
#
Zone America/test      -4:00 test      TS%sT

sudo zic test.zic
ls -l /usr/share/zoneinfo/America/test

After that you can use the zdump command as shown above to verify when the clock will change.

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