ORA-27101: shared memory realm does not exist

In my previous articles i have given the basic idea about multiple oracle errors in detail. I have given the one by one errors.In this article i would like to throw light on most important error coming while working on oracle- ORA-27101: shared memory realm does not exist error. The ORA-27101: shared memory realm does not exist will come due to when local shared memory realm is not accessible. You can see more details in oracle documentation where you will find out multiple types of oracle errors in detail.

Why ” ORA-27101: shared memory realm does not exist ” is coming?

In this section i would like to give you the actual error coming and why that error is coming in detail. I would like to explain multiple scenarios with the error also try to give the resolution of the error.

There are two scenarios due to which this error is occurring :

Scenario 1 :ORACLE_HOME or ORACLE_SID is wrong

There are so many times where ORACLE_HOME and ORACLE_SID is wrong and due to that ORA-27101 error will come.

Scenario 2 : When Database itself is Down

There are so many times the database will be down due to network error and due to that ORA-27101 error will come.We require to check what kind of error is occurring.

Error Description :

[oracle@Amit_db~]$ sqlplus amit_database/Pass@W0RD
SQL*Plus: Release 10.2.0.1.0 - Production on Tue Aug 4 20:14:07 2020
Copyright (c) 1982, 2005, Oracle.  All rights reserved.
ERROR:
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
Linux Error: 2: No such file or directory

I would like to discuss the scenarios in detail.Before that we require to think about the basic cause and its basic solution.

The basic Cause: The basic cause of this error is Unable to locate shared memory realm
Required Action: The DBA need to verify that the realm is accessible

How to resolve the Error –ORA-27101: shared memory realm does not exist ?

In this section i would like to give the 2 scenarios i explained in above paragraph and i will try to give the resolution for the error.

Scenario 1:Invalid ORACLE_HOME and ORACLE_SID:

The basic cause of ORA-27101 is usually due to the invalid ORACLE_HOME and ORACLE_SID parameters at Operating system level.

Steps to check whether ORACLE_HOME and ORACLE_SID Parameters set correct way,

Step 1 : Check whether the ORACLE_HOME is without slash

Step2 : We require to check the trailing slash at first step.

Example :

$ echo $ORACLE_HOME
$ /app/oracle/832/ << This is incorrect because of trailing slash /832/

$ echo $ORACLE_HOME
$ /app/oracle/832<<The oracle home is Correct because slash is not there

Step 3 : Check and Export Oracle SID

[oracle@Amit_db~]$ echo $ORACLE_HOME
/u01/app/oracle/product/10.2.0/amu_01

[oracle@192 ~]$ echo $ORACLE_SID
Amit_test_db

In above case ORACLE_SID is not right, we need to export ORACLE_SID to the valid one which is ora832

[oracle@Amit_db~]$ export ORACLE_SID=ora832
[oracle@Amit_db~]$ sqlplus amit_database/Pass@W0RD
SQL*Plus: Release 10.2.0.1.0 - Production on Tue Aug 4 20:14:07 2020
Copyright (c) 1982, 2005, Oracle.  All rights reserved.
Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options

Using above way we can resolve the issue with ORACLE_SID or ORACLE_HOME and we can resolve the issue.

Resolution :

Basically, to resolve ORA-27101, Once ORACLE_HOME and ORACLE_SID are correct, and then try to start SQL*Plus. 

Scenario 2: Database is down:

We can also face the ORA-27101 error when database is down.So to resolve the issue we require to start the database again.

[oracle@Amit_db~]$ sqlplus sys/sys as sysdba
SQL*Plus: Release 10.2.0.1.0 - Production on tue Aug 4 19:22:38 2020
Copyright (c) 1982, 2005, Oracle.  All rights reserved.
Connected to an idle instance.

SQL> startup
ORACLE instance started.
Total System Global Area 1356784321 bytes
Fixed Size                  1234522bytes
Variable Size             187766663bytes
Database Buffers         102233333333bytes
Redo Buffers               23343334bytes
Database mounted.
Database opened.

Resolution :

To start the database again if it is down.

Using the database start operation you require to connect to the databases.These are the two scenarios for resolving ORA-27101: shared memory realm does not exist with examples.Hope you will get idea about resolving the ORA-27101: shared memory realm does not exist error.If you like this article or if you have any issues with the same kindly comment in comments section.