ora-27101 shared memory realm does not exist linux No such file exists. R3trans -d error 0012

One of the silly error after installation of SAP with Oracle 9i,10g on both RHEL 4 and RHEL 5.This error wasted our one week.But at last now we'are able to find solution.

Description of error:

ORA-01034: ORACLE not  available

ORA-27101: shared memory realm does not exist

After Installation of SAP ECC 5.0 ,on successful startup of Database.

Error : R3trans -d command failed with error 0012 .No connection possible

Here's the Solution:

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

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 andORACLE_SID are correct, and ORACLE_HOME should not have trailing slash. 

For checking on trailing trash:

su - orasid

$ echo $ORACLE_HOME
$ /oracle/SID/102_32/ << Incorrect

$ echo $ORACLE_HOME
$ /oracle/SID/102_32 << Correct

For ORACLE_SID:

$ echo $ORACLE_SID
SID

These steps deadly resolve your this issue.

Also refer two SAP NOTES :

Note 491174 - Composite SAP note for ORA-01034

Note 583861 - UNIX: Errors due to Oracle executable

Thanks,

Gaurav