Inter-process communication (IPC) parameters

Message queue parameters

Parameter	Dflt	Min	Max 64/256/1024	Auto
MSGMAX	2048	512	131072
MSGMNB	4096	4096	131072
MSGMNI	50	50	10000	KVM, Max only
MSGSEG	1	1	1
MSGSSZ	16384	8192	1048576
MSGTQL	200	40	40000	KVM, Max only

 ------------------------------------------------------------
| Parameter|  Dflt |  Min |  Max 64/256/1024|  Auto         |
|----------|-------|------|-----------------|---------------|
| MSGMAX   |   2048|   512|           131072|               |
|----------|-------|------|-----------------|---------------|
| MSGMNB   |   4096|  4096|           131072|               |
|----------|-------|------|-----------------|---------------|
| MSGMNI   |     50|    50|            10000|  KVM, Max only|
|----------|-------|------|-----------------|---------------|
| MSGSEG   |      1|     1|                1|               |
|----------|-------|------|-----------------|---------------|
| MSGSSZ   |  16384|  8192|          1048576|               |
|----------|-------|------|-----------------|---------------|
| MSGTQL   |    200|    40|            40000|  KVM, Max only|
|----------|-------|------|-----------------|---------------|

MSGMAX

Specifies the maximum size of a message.

MSGMNB

Specifies the maximum size of a message queue in bytes. The sum of all messages on a queue cannot be more than MSGMNB.

MSGMNI

Specifies the maximum number of message queues system-wide (id structure).

MSGSEG

The default value is ``1'' and the value of MSGSSZ multiplied by the value of MSGSEG determines the size of the pool available for messages. Keep in mind, so you can balance the amount allocated to this pool with the amount needed by the rest of the system, that this memory is allocated from the Kernel Memory Allocator (KMA). The maximum amount of kernel memory that can be allocated is 16MB.

Historically, MSGSEG specified the number of message segments in the system when segments were limited to 128K.

MSGSSZ

MSGSSZ is not used directly, but is multiplied by MSGSEG to compute the total number of bytes allocated to messages system-wide.

MSGTQL

Specifies the number of message headers in the system and, therefore, the number of outstanding messages. It is suggested that the value be made relatively large to avoid blocking for a message header reservation.

Semaphore parameters

Parameter	Dflt	Min	Max 64/256/1024	Auto
SEMAEM	16384	16384	16384
SEMMNI	150	10	10000	KVM, Max only
SEMMSL	150	25	300
SEMOPM	10	10	20
SEMUME	10	10	20
SEMVMX	32767	32767	32767

 -------------------------------------------------------------
| Parameter|  Dflt |  Min  |  Max 64/256/1024|  Auto         |
|----------|-------|-------|-----------------|---------------|
| SEMAEM   |  16384|  16384|            16384|               |
|----------|-------|-------|-----------------|---------------|
| SEMMNI   |    150|     10|            10000|  KVM, Max only|
|----------|-------|-------|-----------------|---------------|
| SEMMSL   |    150|     25|              300|               |
|----------|-------|-------|-----------------|---------------|
| SEMOPM   |     10|     10|               20|               |
|----------|-------|-------|-----------------|---------------|
| SEMUME   |     10|     10|               20|               |
|----------|-------|-------|-----------------|---------------|
| SEMVMX   |  32767|  32767|            32767|               |
|----------|-------|-------|-----------------|---------------|

SEMAEM

Specifies the adjustment on exit for maximum value, alias semadj. This value is used when a semaphore value becomes greater than or equal to the absolute value of semop(2), unless the program has set its own value.

SEMMNI

Specifies the number of semaphore identifiers in the kernel. This is the number of unique semaphore sets that can be active at any given time.

SEMMSL

Specifies the maximum number of semaphores per semaphore identifier.

SEMOPM

Specifies the maximum number of semaphore operations that can be executed per semop(2) system call.

SEMUME

Specifies the maximum number of undo entries per process.

SEMVMX

Specifies the maximum value of a semaphore.

Shared memory parameters

Parameter	Dflt	Min	Max
SHMMAX	524288	131072	2147483647
SHMMIN	1	1	1
SHMMNI	100	10	1000
SHMSEG	6	6	15
INVLPG_MAX	10	0	255

 -------------------------------------------
| Parameter |  Dflt  |  Min   |  Max       |
|-----------|--------|--------|------------|
| SHMMAX    |  524288|  131072|  2147483647|
|-----------|--------|--------|------------|
| SHMMIN    |       1|       1|           1|
|-----------|--------|--------|------------|
| SHMMNI    |     100|      10|        1000|
|-----------|--------|--------|------------|
| SHMSEG    |       6|       6|          15|
|-----------|--------|--------|------------|
| INVLPG_MAX|      10|       0|         255|
|-----------|--------|--------|------------|

SHMMAX

Specifies the maximum shared memory segment size.

SHMMIN

Specifies the minimum shared memory segment size.

SHMMNI

Specifies the maximum number of shared memory identifiers system-wide.

SHMSEG

Specifies the maximum number of attached shared memory segments per process. The maximum number of shared memory segments that can be attached per process also is dependent on the available unused space the process has. So even if a process has fewer than SHMSEG shared memory segments, it may not be able to attach another because of its limited space.

INVLPG_MAX

INVLPG_MAX defines the threshold at which a global TLB (Translation Lookaside Buffer) flush is done, instead of repeatedly invalidating individual TLB entries. INVLPG_MAX is only used in conjunction with DSHM. When a DSHM buffer is larger than a page size it may be more efficient to flush the entire TLB rather than multiple TLB entries.