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SHMGET(2) System Calls Manual SHMGET(2)

shmgetget shared memory area identifier

#include <sys/shm.h>

shmget(key_t key, size_t size, int shmflg);

() returns the shared memory identifier associated with the key key.

A shared memory segment is created if either key is equal to IPC_PRIVATE, or key does not have a shared memory segment identifier associated with it, and the IPC_CREAT bit is set in shmflg.

If a new shared memory segment is created, the data structure associated with it (the shmid_ds structure, see shmctl(2)) is initialized as follows:

Upon successful completion a positive shared memory segment identifier is returned. Otherwise, -1 is returned and the global variable errno is set to indicate the error.

A shared memory segment is already associated with key and the caller has no permission to access it.
Both IPC_CREAT and IPC_EXCL are set in shmflg, and a shared memory segment is already associated with key.
A shared memory segment is already associated with key and its size is less than the requested size.
A new shared memory identifier could not be created because the system limit for the number of shared memory identifiers has been reached.
was not set in shmflg and no shared memory segment associated with key was found.
There is not enough memory left to create a shared memory segment of the requested size.

ipcrm(1), ipcs(1), mmap(2), shmat(2), shmctl(2), ftok(3)

November 15, 2014 OpenBSD-6.6