I have on the same machine more than 19 Apache Instances installed with the Web Agent.
When I start them one by one, the 9th Apache instance fails to start and reports error :
[06/Jun/2016:08:39:41] [Info] [CA WebAgent IPC]  [CSmSem::getSem] Attempted to attach to non-existent semaphore with key 0xc81d247f
[06/Jun/2016:08:39:41] [Error] [CA WebAgent IPC]  [CSmSem::getSem] Error creating semaphore using key 0xc81d247f - No space left on device (28)
[06/Jun/2016:08:39:41] [Error] SiteMinder Agent Failed to Start the LLAWP process. Failed to initialize the server start mutex.
Web Agent 12SP3CR12 on Apache 2.2 on Redhat 6 64 bit
The issue happens because not enough semaphore are available on the OS. You can check them SMMNS value for the maximum semaphore on RedHat. In the following output, 32000 is the SMMNS.
250 32000 32 128
To solve the issue, increase the semaphore available on the system and adjust the SEMMSL, SEMOPM, and SEMMNI value according to the one you set for the SMMNS one.
A good sample here :