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, int size, int shmflg);

DESCRIPTION

shmget() 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:

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 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.

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

shm_ctime is set equal to the current time. 

RETURN VALUES

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() fails if one or more of the following are true:

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

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. 

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 ALSO

intro(2), shmctl(2), shmop(2), stdipc(3C)

NOTES

The user must explicitly remove shared memory segments after the last reference to them has been removed. 

SunOS 5.1/SPARC  —  Last change: 5 Jul 1990