ORA-27154: post/wait create failed during startup

ORA-27154 is a  quite a common error which many DBA face in day to day activites.I am trying to share what i have learned to resolve it .We are starting the Oracle database  and We receive below error while starting up the database

SQL> startup
ORA-24323: value not allowed
ORA-24323: value not allowed
SQL> startup;
ORA-24323: value not allowed
ORA-27146: post/wait initialization failed

You may also receive an ORA-7445 error in the alert log or an ORA-3113 error.
ORA-3113: end-of-file on communication channel )
Alerts log shows the below error

ORA-27154: post/wait create failed
ORA-27300: OS system dependent operation:semget failed with status: 28
ORA-27301: OS failure message: No space left on device
ORA-27302: failure occurred at: sskgpcreates

Reasons for error may be

1) You increased the processes parameter in the init file and trying to restart the database
2) Server already has many database and You are adding new database to the server

3) Server  OS parameter has undergone the changes

4) You may have stray shared segments
1) We need to either decrease the processes parameter in the database hosted on the server to accomdate the new database
2) We can modify the semaphore kernal settings


You need to remove stray shared memory segments and semaphores.

To get a list of shared memory and semaphore id’s:

ipcs -a

To delete shared memory:

ipcrm -m <shared memory id>

To delete semaphores:

ipcrm -s <semaphore id>

Once you have removed those owned by Oracle and the dba group you are able
to startup the database.