[grid@hostname ~]$ sqlplus / as sysasm
SQL*Plus: Release 11.2.0.3.0 Production on Fri Jul 3 11:31:12 2015
Copyright (c) 1982, 2011, 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: 17
ORA-27301: OS failure message: File exists
ORA-27302: failure occurred at: sskgpcreates
Solution:
You need to remove stray shared memory segments and semaphores.
To get a list of shared memory and semaphore id's:
[oracle@hostname ~]$ ipcs -a
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
0x00000000 425984 oracle 640 4096 0
0x00000000 458753 oracle 640 4096 0
0x1efd4768 491522 oracle 640 4096 0
------ Semaphore Arrays --------
key semid owner perms nsems
0x00000000 1540124 root 666 1
0x96b1110c 5275679 oracle 640 684
0xd95b59b9 4227104 root 666 2
0xa6797c54 5406753 oracle 640 684
0x000003d4 4292642 root 644 1
------ Message Queues --------
key msqid owner perms used-bytes messages
To delete shared memory:
[oracle@hostname ~]$ ipcrm -m 425984
[oracle@hostname ~]$ ipcrm -m 458753
[oracle@hostname ~]$ ipcrm -m 491522
To delete semaphores:
[oracle@hostname ~]$ ipcrm -s 5275679
[oracle@hostname ~]$ ipcrm -s 5406753
[oracle@hostname ~]$ ipcs -a
------ Shared Memory Segments --------
key shmid owner perms bytes nattch status
------ Semaphore Arrays --------
key semid owner perms nsems
0x00000000 1540124 root 666 1
0xd95b59b9 4227104 root 666 2
0x000003d4 4292642 root 644 1
------ Message Queues --------
key msqid owner perms used-bytes messages
Once you have removed those owned by Oracle and the dba group you are able to startup the database.
SQL> startup;
ASM instance started
Total System Global Area 321507328 bytes
Fixed Size 2228024 bytes
Variable Size 294113480 bytes
ASM Cache 25165824 bytes
ASM diskgroups mounted
Explanation
The system crash left the shared memory and semaphores owned by the crashed Oracle instance on the system. These have to be removed before enough resources are available to bring the Oracle instance back up.