man/man2/shmget.2

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 shmget 2 "14 Aug 2006" "SunOS 5.11" "System Calls"
 NAME
shmget - 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 reference 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 minimum 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 TYPEATTRIBUTE VALUE
Interface StabilityStandard


 SEE ALSO

rctladm(1M), Intro(2), setrctl(2), shmctl(2),
shmop(2), ftok(3C), getpagesize(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 zone.max-shm-memory resource
control restricts the total amount of shared memory that can be allocated by a
zone. 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, as well as any
other shared memory segments allocated and still in use by processes in the
zone. 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. The zone.max-shm-ids resource control restricts the total number
of shared memory identifiers that can be allocated by a zone.

See rctladm(1M) and setrctl(2) for information about using resource
controls.