Error:ora-01034:oracle not available ora-27101:shared memory realm does not exist__oracle

Workaround :

1, first look at the Oracle monitoring and Oracle services have been launched. To initiate Oracle listening:
cmd command Line window, input lsnrctl start, enter that start listening.

2, look at ORACLE's SID name, such as the creation of a database, the instance named "ABC", then manually set the Oralce sid,cmd Command window, set ORACLE_SID=ABC

3, Re-enter Sqlplus/nolog, enter
Re-enter Conn/as sysdba; carriage return

4, re-enter startup, enter. This step is to start the Oracle service. If startup is notified that it has been started, you can enter shutdown immediate, and then enter startup after shutdown finishes.

5, after a few seconds, such as command run completed, you can connect. This time, you can enter "select * from User_tables;" Test to see if there are any query results.

6. The reasons for the emergence of ORA-01034 and ORA-27101 are manifold: The primary Oracle current service is unavailable, shared memory realm does not exist because Oracle does not start or does not start properly, Shared memory is not assigned to the current instance. So, start the database by setting the instance name and then using the operating system authentication method. So the database is started normally, there will not be reported ORA-01034 and ORA-27101 two boot exception.