Dealing with the problem of "Connected to an Idle instance" appearing in Sqlplus

Handling of "Connected to an idle instance" issue in Sqlplus:

The issue is explained in the following article:
How to Check the environment Variables for an Oracle Process (document ID 373303.1)

The following is an excerpt from this article:

The most used application of this document are when dealing with the ' Connected to an idle instance ' scenario for a bequeat H SYSDBA connection.
This error indicates, Oracle_sid and Oracle_home in the current session does not match the same environment variables th At were used while the database is started (ORACLE_SID and oracle_home be the strings used to uniquely identify the shared Memory segment of the instance when a connection was done).
Check the Oracle_sid and oracle_home of the background process and compare them with the ones in the current session to FI nd the mismatch.

This issue, Oracle ACS always has records: http://www.xifenfei.com/5197.html

Dealing with the problem of "Connected to an Idle instance" appearing in Sqlplus