shmget - get shared memory segment identifier
#include <sys/types.h> #include <sys/ipc.h> #include <sys/shm.h> int shmget(key_t key, size_t size, int shmflg);
The shmget() function returns the shared memory identifier associated with key.
A shared memory identifier and associated data structure and shared memory segment of at least size bytes (see Intro(2)) are created for key if one of the following are true:
Upon creation, the data structure associated with the new shared memory identifier is initialized as follows:
Shared memory segments must be explicitly removed after the last reference to them has been removed.
Upon successful completion, a non-negative integer representing a shared memory identifier is returned. Otherwise, -1 is returned and errno is set to indicate the error.
The shmget() function will fail if:
A shared memory identifier exists for key but the size of the segment associated with it is less than size and size is not equal to 0.
See attributes(5) for descriptions of the following attributes:
rctladm(1M), Intro(2), setrctl(2), shmctl(2), shmop(2), ftok(3C), getpagesize(3C), attributes(5), standards(5)
The project.max-shm-memory resource control restricts the total amount of shared memory a project can allocate. The zone.max-shm-memory resource control restricts the total amount of shared memory that can be allocated by a zone. The system-imposed maximum on the size of a shared memory segment is therefore a function of the sizes of any other shared memory segments the calling project might have allocated that are still in use, as well as any other shared memory segments allocated and still in use by processes in the zone. For accounting purposes, segment sizes are rounded up to the nearest multiple of the system page size. See getpagesize(3C).
The system-imposed limit on the number of shared memory identifiers is maintained on a per-project basis using the project.max-shm-ids resource control. The zone.max-shm-ids resource control restricts the total number of shared memory identifiers that can be allocated by a zone.
See rctladm(1M) and setrctl(2) for information about using resource controls.
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Created 1996-2021 by Maxim Chirkov
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