⟩ How To Connect the Oracle Server as SYSDBA?
This is Step 4. The best way to connect to the Oracle server as an administrator is to use SQL*Plus. You need to run SQL*Plus with /nolog option and use the CONNECT with blank user name, blank password and AS SYSDBA option. Here is a sample session:
>cd $ORACLE_HOME
>.insqlplus /nolog
SQL> CONNECT / AS SYSDBA
Connected.