ORA-01034:ORACLE not available ORA-27101:shared memory realm does not exist SVR4 Error:2:No such file directory

PROBLEM:
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ORA-01034:ORACLE not available
ORA-27101:shared memory realm does not exist
SVR4 Error:2:No such file directory


SOLUTION:
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There is two probability:

1)The database is down

2)The listener has been restarted in another home