SHMGET(2)

NAME
shmget - get shared memory segment

SYNOPSIS
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/shm.h>

int shmget (key, size, shmflg)
key_t key;
int size, shmflg;

DESCRIPTION
shmget returns the shared memory identifier associated with key.

A shared memory identifier and associated data structure and shared memory segment of size size bytes (see kedef(2)) are created for key if one of the following are true:

    key is equal to IPC_PRIVATE.

    key 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:

    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 low-order 9 bits of shm_perm.mode are set equal to the low-order 9 bits of shmflg. shm_segsz is set equal to the value of size.

    shm_lpid, shm_nattch, shm_atime, and shm_dtime are set equal to 0.

    shm_ctime is set equal to the current time.

RETURN VALUE
Upon successful completion, a non-negative integer, namely a shared memory identifier is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.

ERRORS
shmget will fail if one or more of the following are true:

EINVAL
    size is less than the system-imposed minimum or greater than the system-imposed maximum.

EACCES
    A shared memory identifier exists for key but operation permission (see kedef(2)) as specified by the low-order 9 bits of shmflg would not be granted.

EINVAL
    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 zero.

ENOENT
    A shared memory identifier does not exist for key and (shmflg & IPC_CREAT) is ``false''.

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.

ENOMEM
    A shared memory identifier and associated shared memory segment are to be created but the amount of available physical memory is not sufficient to fill the request.

EEXIST
    A shared memory identifier exists for key but ((shmflg & IPC_CREAT) && (shmflg & IPC_EXCL)) is ``true''.

SEE ALSO
kedef(2), shmctl(2), shmop(2)