ORA-27154:

ORA-27154: post/wait create failed while starting up database\

$ sqlplus '/as sysdba'

SQL*Plus: Release 11.2.0.2.0 Production on Thu May 10 03:14:49 2012

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

Connected to an idle instance.

SYS@BI2400R1 AS SYSDBA 10-MAY-12> startup;
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: sskgpcreate

Solution: This is caused by Kernel parameter setting. Since we were running many databases on a server, we should check our semaphore. Recommended value is

# semaphores: semmsl, semmns, semopm, semmni 

kernel.sem = 250 32000 100 128

In our case it's 

$ /sbin/sysctl -a | grep sem

error: permission denied on key 'kernel.cad_pid'

kernel.sem = 250        32000   100     142

and still we were getting the error as more than 15 databases were running on the server.

We increased the value to 275 as below

# /sbin/sysctl -w kernel.sem=275

added this new value into /etc/sysctl.conf in order the changes persist after system boot

  

and then started the DB.

$ . oraenv

ORACLE_SID = [B12400D1] ? BI2400R1

The Oracle base remains unchanged with value /orasw/app/oracle_test

$ sqlplus '/as sysdba'

SQL*Plus: Release 11.2.0.2.0 Production on Thu May 10 03:18:24 2012

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

Connected to an idle instance.

SYS@BI2400R1 AS SYSDBA 10-MAY-12> startup;

ORACLE instance started.

Total System Global Area 1603411968 bytes

Fixed Size                  2226912 bytes

Variable Size             788530464 bytes

Database Buffers          805306368 bytes

Redo Buffers                7348224 bytes

Database mounted.

Database opened.

SYS@BI2400R1 AS SYSDBA 10-MAY-12> exit