ORA-27123 error during oracle database start

Issue
While starting the oracle database 10g [10.1.0.5.0], we get the following error.

ORA-27123: unable to attach to shared memory segment

Linux Error: 22: Invalid argument
Additional information: 1
Additional information: 9797636

or

ORA-27123: unable to attach to shared memory segment
Linux Error: 22: Invalid argument
Additional information: 1
Additional information: 6651908

Other observation is while we issue "sqlplus / as sysdba" to connect with the database [when database was up and running], it always shows "connected to idle instance".  But, we can connect with the system using oracle SID [like sqplus sys@ORASID as sysdba].

A restart of whole database server has not resolved the issue.

Solution

We have set "stacksize" parameter from the value "10240" to  "unlimited". After that the connection issue has been noticed. Meanwhile as we have not restarted production database we have not noticed any error during restart.
You can check the current stacksize parameter by issuing following command.
$ ulimit -a

Reverting back the stacksize parameter to previous value of "10240" has resolved the entire problem. After that we can connect with the database using "sqlplus / as sysdba" command and start the database without error.

You can also setup the "stacksize" parameter on session basis using the following command.
$ ulimit -s 10240

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