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ORA-27101: shared memory realm does not exist tips

Oracle Error Tips by Burleson Consulting


Oracle docs note this about ORA-27101:

ORA-27101: shared memory realm does not exist

Cause: Unable to locate shared memory realm

Action: Verify that the realm is accessible

The solution in Windows may be to start the Windows services.

MOSC offers valuable information regarding ORA-27101. ORA-27101 is often thrown along with ORA-01034 during database installation.  ORA-27101 is also seen after installation is complete, when attempting to use SQL*Plus.

To resolve this issue with ORA-27101, you should be sure that ORACLE_HOME and ORACLE_SID are correct, and ORACLE_HOME should not have trailing slash.

For checking on trailing trash:

$ /app/oracle/817/ << Incorrect

$ /app/oracle/817 << Correct


$ echo $ORACLE_SID
$ ora817

$ ps -ef | grep smon

(Here, ORACLE_SID setting has been altered from ora817 to ORA817.)

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


I keep receiving ORA-27101 with ORA-01034 after I tried installing the Oracle XE on Windows XP.  Unfortunately, when I connect to the database, ORA-27101 is thrown instead.  Any help?


ORA-27101 may indicate that the system was not able to find the shared memory realm.  So, you could be receiving ORA-27101 because you tried to modify the database parameters such as SGA size.  If this is something that you have done and feel this is why you are encountering ORA-27101, you can try to bring back the original parameters.  Another cause of ORA-27101 is that the instance pointer, or ORACLE_SID, may be gone.  If this is the case, to resolve ORA-27101 you should first try looking for ORACLE_SID. There are several different methods depending on what server you are using:

  • For Unix- try using "echo $ORACLE_SID"
  • For Windows- right click on My Computer?properties?Advance Tab?Environment Variable.  You can view here where or not ORACLE_SID is defined.

If you find in either cases that ORACLE_SID is blank or undefined, this may be the cause of ORA_27101.  You can then set the ORACLE_SID appropriate for the database to resolve ORA-27101.

Reader Comments:

"After running Oracle 11 flawlessly for quite some time, this error suddenly arose in my environment this morning.  After about 5 hours of debugging, and know that nothing new had been installed and configured on my Oracle server, I discovered that this was occurring because my Windows Event Log was full.
Apparently, if the Windows Event Log is full, then Oracle cannot attach to the shared memory realm properly during startup and you'll then get this error when attempting to login as any user.
After cleaning out my various event logs, Oracle is now working properly again."



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