SLOUTION FOR ORA-27154: post/wait create failed

oracle@rac1 ~]$ sqlplus “/as sysdba”

SQL*Plus: Release 11.2.0.1.0 Production on Wed Nov 7 13:59:52 2012

Copyright (c) 1982, 2009, Oracle. All rights reserved.

Connected to an idle instance.

SQL> 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: sskgpsemsper
SQL> exit
Disconnected

  BY seeing this error don’t think about your disk space was filled or cpu utilizations or free  space  is available or not in your swap.   

 1) First you need check about system parameter as  kernel.sem with the command as "sysctl -p" 
 2) cat /etc/sysctl.conf  // helpful to see the parameters. 

              # Controls IP packet forwarding

              net.ipv4.ip_forward = 0

              # Controls source route verification

                  net.ipv4.conf.default.rp_filter = 1

              # Do not accept source routing

                  net .ipv4.conf.default.accept_source_route = 0

              # Controls the System Request debugging functionality of the kernel

                   kernel.sysrq = 0

              # Controls whether core dumps will append the PID to the core filename

              # Useful for debugging multi-threaded applications

                   kernel.core_uses_pid = 1

              # Controls the use of TCP syncookies

                   net.ipv4.tcp_syncookies = 1

              # Controls the maximum size of a message, in bytes

                   kernel.msgmnb = 65536

              # Controls the default maxmimum size of a mesage queue

                   kernel.msgmax = 65536

              # Controls the maximum shared segment size, in bytes

                   kernel.shmmax = 4294967295

             # Controls the maximum number of shared memory segments, in pages

                   kernel.shmall = 268435456

                   fs.file-max = 6815744

                   net.ipv4.ip_local_port_range = 9000 65500

                   net.core.rmem_default = 262144

                   net.core.wmem_default = 262144

                   net.core.rmem_max = 4194304

                   net.core.wmem_max = 1048576

                   fs.aio-max-nr = 1048576

                   kernel.sem = 250 100

3) its not mentioned properly, just  exit from  oracle user. Set the parameter as a root user.

                      # vi /etc/sysctl.conf

              Check and rectifie the value as “kernel.sem = 250 100”

                       #sysctl –p

                   Value will be changed to its originall

                   net.ipv4.ip_forward = 0
                   net.ipv4.conf.default.rp_filter = 1
                   net.ipv4.conf.default.accept_source_route = 0
                   kernel.sysrq = 0
                   kernel.core_uses_pid = 1
                   net.ipv4.tcp_syncookies = 1
                   kernel.msgmnb = 65536
                   kernel.msgmax = 65536
                   kernel.shmmax = 4294967295 
                   kernel.shmall = 268435456
                   fs.file-max = 6815744
                   net.ipv4.ip_local_port_range = 9000 65500
                   net.core.rmem_default = 262144
                   net.core.wmem_default = 262144
                   net.core.rmem_max = 4194304
                  net.core.wmem_max = 1048576
                  fs.aio-max-nr = 1048576
                  kernel.sem = 250 32000 100 128

 4)     Login as a oracle user..

# Su -  oracle

[oracle@rac1 ~]  $

Set your ORACLE_HOME,ORACLE_SID,ORACLE_BASE, then run your bash_profile file

[oracle@rac1 ~]$ sqlplus / as sysdba

SQL*Plus: Release 11.2.0.1.0 Production on Mon Mar 6 13:27:24 2017

Copyright (c) 1982, 2009, Oracle.  All rights reserved.

Connected to an idle instance.

SYS>>startup

ORACLE instance started.

Total System Global Area  217157632 bytes

Fixed Size                  2211928 bytes

Variable Size             159387560 bytes

Database Buffers           50331648 bytes

Redo Buffers                5226496 bytes

Database mounted.

Database opened.

SYS>>