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Changing timezone in RHEL6 from the command line

News NTP -- Network Time Protocol Recommended Links Changing timezone in RHEL6 from the command line Linux Networking Configuration Troubleshooting NTP on Red Hat Linux
RHEL handling of DST change Troubleshooting NTP on Solaris ILO 3 NTP configuration   Humor Etc
Linux systems traditionally store the definition of their timezone in /etc/localtime. This is a binary file with the timezone info, and if we want to change it we need to find the appropriate timezone file from /usr/share/zoneinfo and iether copy it over or create a soft link. It is much better to soft-link it so that timezone information automatically pick up changes to the tzdata package:
ln -sf /usr/share/zoneinfo/GMT /etc/localtime

Once you change it, you will need to restart ntpd as well as any daemons or applications that might use the timezone information directly.

Unfortunately with RHEL/Centos this is not enough and they duplicate some part of this information in the rhel specific file: /etc/sysconfig/clock. for example:  

cat /etc/sysconfig/clock 
ZONE="America/New York" 
UTC=false 
ARC=false
Here is what how the file is explained in documentation

28.1.6. /etc/sysconfig/clock

The /etc/sysconfig/clock file controls the interpretation of values read from the system hardware clock.

The correct values are:

Earlier releases of Red Hat Enterprise Linux used the following values (which are deprecated):

 

Note: in case you need it, there is also applet system-config-date that works via GUI

Temporary change of timezone via TZ environment variable

You can export TZ environment variable to temporarily display date and time according to the  timezone of your liking:
$ export TZ=America/Los_Angeles
$ date

 


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Old News ;-)

[Aug 26, 2015] RHEL 6 Manually Change Time Zone

April 25, 2013 | http://thornelabs.net/2013/04/25/rhel-6-manually-change-time-zone.html

All time zones available on your system can be found in /usr/share/zoneinfo. Change to that directory and browse through the directory structure to find the particular time zone you need.

With your favorite text editor, open /etc/sysconfig/clock and change ZONE= to the particular time zone you need.

For example, to set your system to the Pacific Time Zone, set ZONE= to the following:

ZONE="America/Los_Angeles"

The syntax follows the directory structure in /usr/share/zoneinfo. America/Los_Angeles is located at /usr/share/zoneinfo/America/Los_Angeles.

Once you have edited /etc/sysconfig/clock, create symlink localtime that points to the particular time zone file:

ln -sf /usr/share/zoneinfo/America/Los_Angeles /etc/localtime

Finally, for the changes to take effect, restart any applications using the time zone setting in /etc/sysconfig/clock, or simply restart the system.

[Aug 25, 2015] Fixing Date, Time and Zone on RHEL 6 command line

April 10, 2012 | dev.chetankjain.net

Had to fix all time related issues on a remote RHEL 6 server which runs without any windowing system. Plain ol' command line. Documenting steps here for future reference:

Check to see if your date and timezone settings are accurate:
# date
# cat /etc/sysconfig/clock

The server I accessed had wrong settings for both the commands. Here are the steps I used to correct:

Find out your timezone from the folder /usr/share/zoneinfo
# ls /usr/share/zoneinfo

Mine was pointing to America/EDT instead of Asia/Calcutta

Update and save the /etc/sysconfig/clock file to
# sudo vi /etc/sysconfig/clock
ZONE="Asia/Calcutta"
UTC=true
ARC=false

Remove the /etc/localtime
# sudo rm /etc/localtime

Create a new soft link to your time zone
# cd /etc
# sudo ln -s /usr/share/zoneinfo/Asia/Calcutta /etc/localtime
# ls -al localtime
Now it should show the link to your time zone

Set your hardware clock to UTC
# sudo hwclock --systohc --utc
# hwclock --show

Update your time from a NTP server (Red Hat NTP server used here)
# sudo ntpdate clock.redhat.com
10 Apr 22:08:27 ntpdate[25695]: adjust time server 66.187.233.4 offset 0.004185 sec

Finally verify the date now
#date --utc
Tue Apr 10 16:39:56 UTC 2012

#date
Tue Apr 10 22:09:58 IST 2012

Add the above ntpdate command in your server startup script or in a cron job to automatically set the system time. The list of ntp servers can be found here: https://support.ntp.org/bin/view/Servers/StratumOneTimeServers



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