The default values for the kernel parameters are located in the /proc/sys/kernel/ directory. These are set default values provided by the kernel or values specified by a user by using sysctl.

The following kernel parameters configure limits for the msg* and shm* System V IPC (sysvipc) system calls:

msgmax

Defines the maximum allowed size in bytes of any single message in a message queue. This value must not exceed the size of the queue (msgmnb). Use the sysctl kernel.msgmax command to determine the current msgmax value on your system.

msgmnb

Defines the maximum size in bytes of a single message queue. Use the sysctl msgmnb command to determine the current msgmnb value on your system.

msgmni

Defines the maximum number of message queue identifiers, and therefore the maximum number of queues. Use the sysctl kernel.msgmni command to determine the current msgmni value on your system.

shmall

Defines the total amount of shared memory pages that can be used on the system at one time. For example, a page is 4096 bytes on the AMD64 and Intel 64 architecture. Use the sysctl kernel.shmall command to determine the current shmall value on your system.

shmmax

Defines the maximum size in bytes of a single shared memory segment allowed by the kernel. Shared memory segments up to 1Gb are now supported in the kernel. Use the sysctl kernel.shmmax command to determine the current shmmax value on your system.

shmmni

Defines the system-wide maximum number of shared memory segments. The default value is 4096 on all systems.