Ora 27101 error

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In [1], it has listed some tips for resolving Oracle exception:

• ORA-27101: shared memory realm does not exist

In this article, we will show you yet another tip of resolving ORA-27101.

The Background

There are two teams share the same DB server in our environment. Team A started an Oracle instance without shutting it down. As a team B member, how do you figure out how to shut it down?

Steps

1. Find out the SID name:
   • ps -ef | grep smon (or pmon)
   • For example, the command shows:
     • oracle 32607 1 0 10:12 ? 00:00:03 ora_smon_SOAR2
   • So, we know the SID is named SOAR2.
     
2. Find out Oracle Home path:
   • Use pmap command to report the memory map of smon process. For example, we issue: «pmap 32607» and one of the output line shows:
     • 00002b3f57270000 4K rwx— /disk2/home/oracle/atg/OracleDB_11.2.0.2/product/11.2.0/dbhome_1/lib/libocrutl11.so
3. Setup ORACLE_HOME and ORACLE_SID environment variable
   • For example, we have set them using Linux bash:
     • export ORACLE_HOME=/disk2/home/oracle/atg/OracleDB_11.2.0.2/product/11.2.0/dbhome_1
     • export ORACLE_SID=SOAR2

However, after we started sqlplus and tried to shutdown our instance, we got:

$sqlplus «/ as sysdba

SQL*Plus: Release 11.2.0.2.0 Production on Wed Apr 25 17:15:08 2012

Copyright (c) 1982, 2010, Oracle. All rights reserved.

Connected to an idle instance.

SQL> shutdown immediate;
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
Linux-x86_64 Error: 2: No such file or directory

The Issue

The problem is that /data/home is a symbolic link to /disk2/home directory. Oracle does not recognize one name used in Oracle Home path if you started it using another name.

To check what the environment variable ORACLE_HOME was set, you can check the process environment (/proc/<pid>/environ) . For example, from the following file:

• /proc/32607/environ

we have found that ORACLE_HOME was set to be:

• /data/home/oracle/atg/OracleDB_11.2.0.2/product/11.2.0/dbhome_1

After we have reset our ORACLE_HOME to the new path, we have resolved ORA-27101 issue.

References

1. ORA-27101: shared memory realm does not exist tips
2. ORA-01031: insufficient privileges

ORA-27101: shared memory realm does not exist
Cause: Unable to locate shared memory realm
Action: Verify that the realm is accessible

Reference: Oracle Documentation

There may be 2 scenarios, which may lead you to encounter ORA-27101
1) Invalid ORACLE_HOME and ORACLE_SID
2) Database is down

[oracle@192 ~]$ sqlplus scott/tiger
SQL*Plus: Release 10.2.0.1.0 - Production on Wed May 22 16:48:05 2013
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

Scenario 1: Invalid ORACLE_HOME and ORACLE_SID:

ORA-27101 is usually due to the invalid ORACLE_HOME and ORACLE_SID parameters at OS level. You should investigate that ORACLE_HOME and ORACLE_SID are set correctly, and ORACLE_HOME should be without trailing slash.

[oracle@192 ~]$ echo $ORACLE_HOME
/u01/app/oracle/product/10.2.0/db_1

[oracle@192 ~]$ echo $ORACLE_SID
testdb

In our case ORACLE_SID was not correct, we need to export ORACLE_SID to the valid one which is ora10g

[oracle@192 ~]$ export ORACLE_SID=ora10g
[oracle@192 ~]$ sqlplus scott/tiger
SQL*Plus: Release 10.2.0.1.0 - Production on Wed May 22 16:52:11 2013
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

Scenario 2: Database is down:

You may also face it when the database is down, to solve ORA-27101 you may have to start the database only

[oracle@192 ~]$ sqlplus sys/sys as sysdba
SQL*Plus: Release 10.2.0.1.0 - Production on Wed May 22 17:07:38 2013
Copyright (c) 1982, 2005, Oracle.  All rights reserved.
Connected to an idle instance.

SQL> startup
ORACLE instance started.
Total System Global Area 1224736768 bytes
Fixed Size                  1219112 bytes
Variable Size             167773656 bytes
Database Buffers         1040187392 bytes
Redo Buffers               15556608 bytes
Database mounted.
Database opened.

Related Posts:
ORA-04031: unable to allocate n bytes of shared memory
— ORA-01034: ORACLE not available
— ORA-01157: cannot identify/lock data file string — see DBWR trace file
— ORA-00849: SGA_TARGET cannot be set to more than MEMORY_MAX_TARGET
— ORA-00604: error occurred at recursive SQL level string
— ORA-00600: internal error code
— ORA-00257: archiver error. Connect internal only, until freed