Timezone information

How to set timezone in postgreSQL database to pick operating system level
timezone information.

In postgresql.conf there exists "timezone" parameter whose value can be set.
However this value needs to be in format 'US/Pacific', 'Asia/Calcutta' and
so on to work correctly.

Is there any database query to get operating system level timezone
information and then set accordingly.

Took a look into pg_timezone_names table and

SET [ SESSION | LOCAL ] TIME ZONE { timezone | LOCAL | DEFAULT }

When postgres is installed on IST timezone windows operating system,
registry key
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\TimeZoneInformation
has TimeZoneKeyName set as "India Standard Time". However post installation
postgresql.conf has timezone information set as 'Asia/Calcutta', is there
any binary which can be executed?

Regards...