Параметры shm в ядре

/proc/sys/kernel/shmmax - The maximum size of a shared memory segment.
/proc/sys/kernel/shmmni - The maximum number of shared memory segments.
/proc/sys/kernel/shmall - The maximum amount of shared memory that can be allocated (в страницах! страница - 4 кб)

Эти настройки можно очень удобно просмотреть утилитой ipcs:

ipcs -lm

------ Shared Memory Limits --------
max number of segments = 8192
max seg size (kbytes) = 262144
max total shared memory (kbytes) = 8388608
min seg size (bytes) = 1

А текущее использование можно посмотреть вот так:

ipcs -um

------ Shared Memory Status --------
segments allocated 450
pages allocated 1605547
pages resident 464458
pages swapped 14
Swap performance: 0 attempts 0 successes

(с) http://publib.boulder.ibm.com/infocenter/wmqv6/v6r0/index.jsp?topic=/com.ibm.mq.amq1ac.doc/lq10410_.htm