ORA-27123 unable to attach to shared memory segment

Error Description:
------------------------
Whenever you try to start your database instance it failed with error as follows.

SQL> startup
ORA-27123: unable to attach to shared memory segment
Solaris-AMD64 Error: 13: Permission denied

Cause of the Problem:
----------------------
As the error suggested permission denied so there is problem in proper permission settings. In the $ORACLE_HOME and in $ORACLE_HOME/bin proper permission is not set and hence error comes.

Solution of The Problem:
-----------------------------
You need to change the "umask" to the required 022, set the proper permission on $ORACLE_HOME, $ORACLE_HOME/bin directories. In my computer, I ran the following.

1)Log on as root and change permission.
bash-3.00$ su
Password:
# umask 022
# cd $ORACLE_HOME
# chmod 755 *
# cd $ORACLE_BASE/admin/$ORACLE_SID
# chmod 755 *
# cd $ORACLE_HOME/bin
# chmod 6751 oracle
# exit

2)Log on normal user and log on to database.
bash-3.00$ sqlplus / as sysdba

SQL*Plus: Release 10.2.0.1.0 - Production on Wed May 14 23:40:12 2008

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Connected to:
Oracle Database 10g Enterprise Edition Release 10.2.0.1.0 - Production
With the Partitioning, OLAP and Data Mining options