shmget - get shared memory segment identifier
int shmget(key_t key, size_t size, int shmflg);
shmget 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:
key is equal to IPC_PRIVATE.
key does not already have a shared memory identifier associated with
it, and (shmflg<b>&IPC_CREAT) is true.
Upon creation, the contents of the shared memory segment are initialized
to zero, and the data structure associated with the new shared memory
identifier is initialized as follows:
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 access permission bits of shm_perm.mode are set equal to the
access permission bits of shmflg. shm_segsz is set equal to the
value of size.
shm_lpid, shm_nattch shm_atime, and shm_dtime are set equal to 0.
shm_ctime is set equal to the current time.
shmget fails if one or more of the following are true:
EINVAL size is less than the system-imposed minimum or greater
than the system-imposed maximum.
EACCES A shared memory identifier exists for key but operation
permission [see intro(2)] as specified by the low-order 9
bits of shmflg would not be granted.
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<b>&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 associated shared memory
segment are to be created but the amount of available
memory is not sufficient to fill the request.
EEXIST A shared memory identifier exists for key but both
(shmflg<b>&IPC_CREAT) and (shmflg<b>&IPC_EXCL) are true.
intro(2), shmctl(2), shmop(2), stdipc(3C), ipcs(1), ipcrm(1).
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 indicate the error.
The user must explicitly remove shared memory segments after the last
reference to them has been removed.
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