SHMGET(2) — HP-UX

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 glossary) 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.

EXAMPLES

The following call to shmget returns a unique shmid for the newly created shared memory segment of 4096 bytes:

int myshmid;

myshmid = shmget (IPC_PRIVATE, 4096, 0600);

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 glossary) 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”.

HARDWARE DEPENDENCIES

Series 500
Shared memory segments larger than 16384 bytes are paged virtual segments; otherwise they are non-paged virtual segments.

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.

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