shmget(2) System Calls shmget(2)NAMEshmget - get shared memory segment identifier
SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>
int shmget(key_t key, size_t size, int shmflg);
DESCRIPTION
The shmget() function 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:
· The key argument is equal to IPC_PRIVATE.
· The key argument 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 values of 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.
· The values of shm_lpid, shm_nattch shm_atime, and shm_dtime are
set equal to 0.
· The shm_ctime is set equal to the current time.
Shared memory segments must be explicitly removed after the last refer‐
ence to them has been removed.
RETURN VALUES
Upon successful completion, a non-negative integer representing a
shared memory identifier is returned. Otherwise, −1 is returned and
errno is set to indicate the error.
ERRORS
The shmget() function will fail if:
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.
EEXIST A shared memory identifier exists for key but both
(shmflg&IPC_CREAT) and (shmflg&IPC_EXCL) are true.
EINVAL The size argument is less than the system-imposed mini‐
mum or greater than the system-imposed maximum. See
NOTES.
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 0.
ENOENT A shared memory identifier does not exist for key and
(shmflg&IPC_CREAT) is false.
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.
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. See NOTES.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Standard │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOrctladm(1M), intro(2), setrctl(2), shmctl(2), shmop(2), ftok(3C), get‐
pagesize(3C), attributes(5), standards(5)NOTES
The project.max-shm-memory resource control restricts the total amount
of shared memory a project can allocate. The system-imposed maximum on
the size of a shared memory segment is therefore a function of the
sizes of any other shared memory segments the calling project might
have allocated that are still in use. For accounting purposes, segment
sizes are rounded up to the nearest multiple of the system page size.
See getpagesize(3C).
The system-imposed limit on the number of shared memory identifiers is
maintained on a per-project basis using the project.max-shm-ids
resource control.
See rctladm(1M) and setrctl(2) for information about using resource
controls.
SunOS 5.10 4 Sep 2003 shmget(2)
