Restricted Mode of Instaance Startup

You can start an instance in restricted mode(or later alter an existing instance to be in restrcted mode). This restricts connections to only those users who have been granted the RESTRICTES SESSION system privilege.

Forced Startup in Abnormal Situations

In unusual circumstances , a previous instance might not have been shut down cleanly. For example, one of the instance's processes might not have terminated properly . In such situations, the database can return an error during normal instance startup. To reslove this problem, You must terminate all remnant Oracle processes of the previous instance before starting the new instance.