Question { IBM, 21798 }

What is semaphores and why it is used?

Answer

On some UNIX® systems, the system administrator can edit
the /etc/master file and define limits for IPC mechanisms
(semaphores, shared memory segments, and message queues).
The problem with this method is that the higher the limits,
the more memory the operating system uses, and performance
can be adversely affected.

AIX uses a different method. In AIX®, upper limits are
defined for the IPC mechanisms, which are not configurable.
The individual IPC data structures are allocated and
deallocated as needed, so memory requirements depend on the
current system usage of IPC mechanisms.

Semaphores 4.3.0 4.3.1 4.3.2 5.1 5.2 5.3 6.1
Maximum number of semaphore IDs for 32-bit kernel 4096 4096
131072 131072 131072 131072 N/A
Maximum number of semaphore IDs for 64-bit kernel 4096 4096
131072 131072 131072 1048576 1048576
Maximum semaphores per semaphore ID 65535 65535 65535 65535
65535 65535 65535

Question { IBM, 21798 }

What is semaphores and why it is used?

Answer

Semaphores (On UNIX)

• is a synchronization primitive
• is a form of IPC, semaphore is not usedfor exchanging
large amounts of data,as is pipe; but are intended to let
multiple processes synchronize their operations.