Connect SQLPLUS back door with Preliminary connection (PERLIM) in Oracle
When you are not able to login as sysdba in your own database then you have one back door entry to connect to the Oracle Database with using PERLIM parameter with SQLPLUS. In this you have limited access to Database for do basic DBA task.
Following are the ways to connect to database:
First method, Use perlim directly in the SQLPLUS command:
sqlplus -prelim / as sysdba
Second method, Set the parameter perlim ON for connectivity as shown below:
set _prelim on
connect / as sysdba