shmget.2freebsd

Langue: en

Version: 265945 (debian - 07/07/09)

Section: 2 (Appels système)

Sommaire


BSD mandoc

NAME

shmget - obtain a shared memory identifier

LIBRARY

Lb libc

SYNOPSIS

In machine/param.h In sys/types.h In sys/ipc.h In sys/shm.h Ft int Fn shmget key_t key size_t size int flag

DESCRIPTION

Based on the values of Fa key and Fa flag , Fn shmget returns the identifier of a newly created or previously existing shared memory segment. The key is analogous to a filename: it provides a handle that names an IPC object. There are three ways to specify a key:

The mode of a newly created IPC object is determined by OR 'ing the following constants into the Fa flag argument:

SHM_R
Read access for user.
SHM_W
Write access for user.
( SHM_R>>3
Read access for group.
( SHM_W>>3
Write access for group.
( SHM_R>>6
Read access for other.
( SHM_W>>6
Write access for other.

When creating a new shared memory segment, Fa size indicates the desired size of the new segment in bytes. The size of the segment may be rounded up to a multiple convenient to the kernel (i.e., the page size).

RETURN VALUES

Upon successful completion, Fn shmget returns the positive integer identifier of a shared memory segment. Otherwise, -1 is returned and errno set to indicate the error.

ERRORS

The Fn shmget system call will fail if:
Bq Er EINVAL
Size specified is greater than the size of the previously existing segment. Size specified is less than the system imposed minimum, or greater than the system imposed maximum.
Bq Er ENOENT
No shared memory segment was found matching Fa key , and IPC_CREAT was not specified.
Bq Er ENOSPC
The kernel was unable to allocate enough memory to satisfy the request.
Bq Er EEXIST
IPC_CREAT and IPC_EXCL were specified, and a shared memory segment corresponding to Fa key already exists.

SEE ALSO

shmat(2), shmctl(2), shmdt(2), ftok(3)