Oracle Database timezone update

How to update Oracle Database Time Zone:

First make a note of the existing timezone with the below query.

select SYSTIMESTAMP, current_TIMESTAMP from dual;

select to_char(sysdate,'DD-MON-YYYY HH24:MI:SS') from dual;

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To change timezone:(OS Level)

$tzselect

$timedatectl set-timezone <new_time_zone>

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Steps to be followed to change DBTIMEZONE:

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SQL> SELECT SESSIONTIMEZONE, DBTIMEZONE FROM DUAL;

SESSIONTIMEZONE         DBTIME

----------------        ------

-06:00                  -07:00

SQL> ALTER DATABASE SET TIME_ZONE='Canada/Mountain';

Database altered.

SQL> ALTER DATABASE SET TIME_ZONE='-06:00';

Database altered.

SQL> shutdown immediate;

SQL> Startup;

SQL> SELECT SESSIONTIMEZONE, DBTIMEZONE FROM DUAL;

SESSIONTIMEZONE         DBTIME

------------------      -----------

-06:00                  -06:00