ORA-27123: unable to attach to shared memory segment

Hello,

Of late, in one of our test unix (Sun Solaris) boxes, a database user is trying to connect to the database, but getting an error “ORA-27123: unable to attach to shared memory segment” with permission denied issue.

Initially we thought that there might be an issue with SGA memory area or may be an issue with the shared memory segments and semaphores for the instance allocated. But later we found that the permission on ORACLE_HOME directory got changed accidentally with the full permission.

Here are our findings:

$ sqlplus testusr/password@testdb

SQL*Plus: Release 10.2.0.2.0 - Production on Tue Jan 27 20:53:44 2009

Copyright (c) 1982, 2005, Oracle. All Rights Reserved.

ERROR:
ORA-01034: ORACLE not available
ORA-27123: unable to attach to shared memory segment
SVR4 Error: 13: Permission denied 

As per Oracle Error Messages:

Error: ORA-27123: unable to attach to shared memory segment
Cause: shmat() call failed
Action: check permissions on segment, contact Oracle support

Check the oracle executable file permission.

$ cd $ORACLE_HOME/bin
$ ls -l oracle
-rwxrwxr-x 1 oracle dba 119582976 Feb 3 2008 oracle

Here the oracle file permission has -rwxrwxr-x i.e. 775, but this file must have the permission -rwsr-s- -x i.e. 6751

Change the permissions for oracle file.

$ cd $ORACLE_HOME/bin
$ chmod 6751 oracle
$ ls -l oracle
-rwsr-s--x 1 oracle dba 119582976 Feb 3 2008 oracle

After changing the permissions on oracle executable file, all the users are now able to connect to the database without any errors.

Note: For further information refer the Oracle Metalink Note ID: 1011995.6 Subject: COMMON ORACLE PERMISSION PROBLEMS ON UNIX.