Changing timezone in RHEL6 from the command line

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

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:

• UTC=<value>, where <value> is one of the following boolean values:
  • true or yes — The hardware clock is set to Universal Time.
  • false or no — The hardware clock is set to local time.
• ARC=<value>, where <value> is the following:
  • false or no — This value indicates that the normal UNIX epoch is in use. Other values are used by systems not supported by Red Hat Enterprise Linux.

   

• SRM=<value>, where <value> is the following:
  • false or no — This value indicates that the normal UNIX epoch is in use. Other values are used by systems not supported by Red Hat Enterprise Linux.

   

• ZONE=<filename> — The time zone file under /usr/share/zoneinfo that /etc/localtime is a copy of. The file contains information such as:

  ZONE="America/New York"
  

  Note that the ZONE parameter is read by the Time and Date Properties Tool (system-config-date), and manually editing it does not change the system timezone.

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

• CLOCKMODE=<value>, where <value> is one of the following:
  • GMT — The clock is set to Universal Time (Greenwich Mean Time).
  • ARC — The ARC console's 42-year time offset is in effect (for Alpha-based systems only).

 

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

NEWS CONTENTS

• 20150826 : RHEL 6 Manually Change Time Zone ( April 25, 2013 , http://thornelabs.net/2013/04/25/rhel-6-manually-change-time-zone.html )
• 20150825 : Fixing Date, Time and Zone on RHEL 6 command line ( April 10, 2012 , dev.chetankjain.net )

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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