(1) Required Privileges
You must have the ALTER DATABASE system privilege.
To specify the RECOVER clause, you must also have the SYSDBA system privilege.
(2) Open the database -- READ ONLY / READ WRITE:
The following statement opens the database in read-only mode:
ALTER DATABASE OPEN READ ONLY;
The following statement opens the database in read/write mode and clears the online redo logs:
ALTER DATABASE OPEN READ WRITE RESETLOGS;
(3) enable and disable a restricted session
alter system enable restricted session;
alter system disable restricted session;
to identify if the database is in that mode
select logins from v$instance;
ALTER SYSTEM QUIESCE RESTRICTED;