Opening database in read only or read write mode or restricted mode

To prevent the user to modify the data you can open the database in read only mode by following command

ALTER DATABASE OPEN READ ONLY

TO make database read write

ALTER DATABASE OPEN READ WRITE

In READ WRITE mode the users can generate online redo log files.

Opening database in restricted mode:

You can open database in restricted mode to perform database structure maintenance or import export of database.

STARTUP RESTRICTED

To place the instance in the restricted mode

ALTER SYSTEM ENABLE RESTRICTED SESSION;

Enabling restricted session mode ensures that in future only those users with restricted session privilege can login.

You can also disable the restricted session mode by DISABLE RESTRICTED SESSION command