SHMGET(2) System Calls Manual SHMGET(2)
shmget -- get shared memory segment
Standard C Library (libc, -lc)
shmget(key_t key, size_t size, int shmflg);
shmget() returns the shared memory identifier associated with the 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 both the IPC_CREAT bit
and the IPC_EXCL bit are set in shmflg, and key has a shared memory
segment identifier associated with it already, the operation will fail.
If a new shared memory segment is created, the data structure associated
with it (the shmid_ds structure, see shmctl(2)) is initialized as
o shm_perm.cuid and shm_perm.uid are set to the effective uid of the
o shm_perm.gid and shm_perm.cgid are set to the effective gid of the
o shm_perm.mode is set to the lower 9 bits of shmflg.
o shm_lpid, shm_nattch, shm_atime, and shm_dtime are set to 0.
o shm_ctime is set to the current time.
o shm_segsz is set to the value of size.
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.
[EACCES] A shared memory segment is already associated with key
and the caller has no permission to access it.
[EEXIST] Both IPC_CREAT and IPC_EXCL are set in shmflg, and a
shared memory segment is already associated with key.
[EINVAL] No shared memory segment is to be created, and a
shared memory segment exists for key, but the size of
the segment associated with it is less than size,
which is non-zero.
A shared memory segment is to be created, and size is
less than the system imposed minimum, or greater than
the system imposed maximum (refer to the kern.ipc
values in sysctl(7)).
[ENOENT] IPC_CREAT is not set in shmflg and no shared memory
segment associated with key was found.
[ENOMEM] There is not enough memory left to create a shared
memory segment of the requested size.
[ENOSPC] A new shared memory identifier could not be created
because the system limit for the number of shared
memory identifiers has been reached.
ipcrm(1), ipcs(1), mmap(2), shmat(2), shmctl(2), ftok(3), sysctl(7)
The shmget system call conforms to X/Open System Interfaces and Headers
Issue 5 (``XSH5'').
Shared memory segments appeared in the first release of AT&T System V
NetBSD 6.1.5 October 27, 2008 NetBSD 6.1.5