A ORA-01034: ORACLE not available

RROR:
A ORA-01034: Oracle not available
ORA-27101: shared memory realm does not exist
Linux-x86_64 Error: 2: No such file or directory
Process ID: 0
Session ID: 0 Serial number: 0

I encountered a problem. I have been tossing for more than half an hour today. I don't pay attention to the details.

There are only two reasons

1. The service is not started.

This cause is easy to understand.

2. The link listening is incorrect.

Clearly using the as sysdba can be linked, and adding a service name to the back will not work. At the beginning, I searched for online materials for whatever reason, and finally I carefully watched the listener.

One is

Services Summary...
Service "orcl" has 1 instance (s ).
Instance "ORCL", status UNKNOWN, has 1 handler (s) for this service...
Service "orcl. localdomain" has 1 instance (s ).

Modify the service name.

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