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


Sometimes you can get ” ORA-01034: ORACLE not available ” error.

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

This errors are taken because of the following reasons.
  • 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.

Check the Oracle SID and Oracle Home, if they are Ok or not ?
[oracle@MSDBdbadm01:/home/oracle:> echo $ORACLE_SID

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

Compare Oracle SID and Oracle home from oratab file. oratab files are exist under the following paths.


If they are not set correctly, then set them as follows.
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:\> sqlplus / as sysdba

SQL> startup



Do you want to learn Oracle Database for Beginners, then read the following articles.



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About Mehmet Salih Deveci

I am Founder of SysDBASoft IT and IT Tutorial and Certified Expert about Oracle & SQL Server database, Goldengate, Exadata Machine, Oracle Database Appliance administrator with 10+years experience. I have OCA, OCP, OCE RAC Expert Certificates I have worked 100+ Banking, Insurance, Finance, Telco and etc. clients as a Consultant, Insource or Outsource. I have done 200+ Operations in this clients such as Exadata Installation & PoC & Migration & Upgrade, Oracle & SQL Server Database Upgrade, Oracle RAC Installation, SQL Server AlwaysOn Installation, Database Migration, Disaster Recovery, Backup Restore, Performance Tuning, Periodic Healthchecks. I have done 2000+ Table replication with Goldengate or SQL Server Replication tool for DWH Databases in many clients. If you need Oracle DBA, SQL Server DBA, APPS DBA,  Exadata, Goldengate, EBS Consultancy and Training you can send my email adress mehmetsalih.deveci@outlook.com. -                                                                                                                                                                                                                                                 - Oracle DBA, SQL Server DBA, APPS DBA,  Exadata, Goldengate, EBS ve linux Danışmanlık ve Eğitim için  mehmetsalih.deveci@outlook.com a mail atabilirsiniz.

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