If you change settings with the ALTER SESSION command, or certain SQL*Plus settings with the SQL*Plus SET command, you will lose these changes after you log off.
On startup, SQL* Plus will use the default values again.
To preserve the changes, you can store these SQL and SQL*Plus commands in a file with the special name, login.sql.
This file is automatically executed when you start SQL*Plus, or even when you change connections within a SQL*Plus session with the CONNECT command.
SQL*Plus would find this file in the directory it starts in or via the SQLPATH Registry setting.