shmget(2)
NAME
shmget − get shared memory segment
SYNTAX
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
int shmget (key, size, shmflg)
key_t key;
int size, shmflg;
DESCRIPTION
The shmget system call returns the shared memory identifier associated with key. A shared memory identifier and associated data structure and shared memory segment of size size bytes are created for key if one of the following are true:
The key is equal to IPC_PRIVATE . For further information, see intro(2).
The key does not already have a shared memory identifier associated with it, and (shmflg & IPC_CREAT ) is "true".
Upon creation, the data structure associated with the new shared memory identifier is initialized as follows:
The shm_perm.cuid,shm_perm.uid,shm_perm.cgid, and shm_perm.gid are set equal to the effective user ID and effective group ID, respectively, of the calling process.
The low-order 9 bits of shm_perm.mode are set equal to the low-order 9 bits of shmflg. The shm_seqsz is set equal to the value of size.
The shm_lpid,shm_nattch,shm_atime, and shm_dtime are set equal to 0. The shm_ctime is set equal to the current time.
Upon successful completion, a non-negative integer, namely a shared memory identifier is returned. Otherwise, a value of -1 is returned and errno is set to indicated the error.
DIAGNOSTICS
The shmget system call will fail if one or more of the following are true:
[EINVAL] The size is less than the system imposed minimum or greater than the system imposed maximum.
[EACCES] A shared memory identifier exists for key but operations permission as specified by the low-order 9 bits of shmflg would not be granted. For further information, see intro(2).
[EINVAL] 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 zero.
[ENOENT] A shared memory identifier does not exist for key and (shmflg & IPC_CREAT ) is "false".
[ENOSPC] A shared memory identifier is to be created but the system imposed limit on the maximum number of allowed shared memory identifiers system wide would be exceeded.
[ENOMEM] A shared memory identifier and associate shared memory segment are to be created by the amount of available physical memory is not sufficient to fill the request.
[EEXIST] A shared memory identifier exists for key but ((shmflg & IPC_CREAT ) & (shmflg & IPC_EXCL )) is "true".