ORA-01034: ORACLE not available and ORA-27101: shared memory realm does not exist

Sometimes you can get ” ORA-01034: ORACLE not available ORA-27101: shared memory realm does not exist ” error.

ORA-01034: ORACLE not available

Details of error are as follows.

ORA-01034: ORACLE not available

Cause: Oracle was not started up. Possible causes include the following:- The SGA requires more space than was allocated for it.

– The operating-system variable pointing to the instance is improperly defined.

Action: Refer to accompanying messages for possible causes and correct the problem mentioned
in the other messages. If Oracle has been initialized, then on some operating systems,

verify that Oracle was linked correctly. See the platform specific Oracle documentation.

ERROR:
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
Linux-x86_64 Error: 2: No such file or directory

ORA-01034: ORACLE not available ORA-27101: shared memory realm does not exis

• Oracle Instance is not started.
• ORACLE_SID or ORACLE_HOME or both are not properly defined.
• Size of SGA is smaller than an Oracle Instance requires.
• Remote user might face it due to improper configuration of Listener.
• Refer to accompanying messages for possible causes and correct the problem.

Linux-x86_64 Error: 2: No such file or directory

[oracle@MSDBdbadm01:/home/oracle:> echo $ORACLE_SID

[oracle@MSDBdbadm01:/home/oracle:> echo $ORACLE_HOME

/etc/oratab

/var/opt/oracle/oratab

Unix/Linux :

[oracle@MSDBdbadm01:/home/oracle:> ORACLE_SID=INSTANCE_NAME

[oracle@MSDBdbadm01:/home/oracle:> export ORACLE_SID

[oracle@MSDBdbadm01:/home/oracle:> export ORACLE_HOME=/u01/app/product/12.2.0/dbhome_1

[oracle@MSDBdbadm01:/home/oracle:> sqlplus / as sysdba

SQL> startup

Window :

C:\> set ORACLE_SID=INSTANCE_NAME
C:\> sqlplus / as sysdba

SQL> startup

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