- NetBSD Manual Pages
SHMGET(2) NetBSD System Calls Manual SHMGET(2)
Powered by man-cgi (2021-06-01).
Maintained for NetBSD
by Kimmo Suominen.
Based on man-cgi by Panagiotis Christias.
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 seg-
ment 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 fol-
· shm_perm.cuid and shm_perm.uid are set to the effective uid of the
· shm_perm.gid and shm_perm.cgid are set to the effective gid of the
· shm_perm.mode is set to the lower 9 bits of shmflg.
· shm_lpid, shm_nattch, shm_atime, and shm_dtime are set to 0.
· shm_ctime is set to the current time.
· 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 val-
ues 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 mem-
ory 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 8.1 October 27, 2008 NetBSD 8.1