How to change time-zone settings from the command line

Use timedatectl

sudo timedatectl set-timezone <timeszone>

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Examples:

• Timezone as EST

  sudo timedatectl set-timezone EST
  

• Timezone as UTC

  sudo timedatectl set-timezone UTC
  

• Listing all valid Timezones

  timedatectl list-timezones
  

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This command is perfect for automation scripts since it doesn't require any user interaction while compared to the other given answer based on dpkg-reconfigure tzdata.

As root you have to execute:

dpkg-reconfigure tzdata

A menu based tool should be started that allows you to change the timezone.

The following also work. For GMT:

ln -sf /usr/share/zoneinfo/GMT /etc/localtime

For EST:

ln -sf /usr/share/zoneinfo/EST /etc/localtime