NAME

msgget − get message queue

SYNOPSIS

#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/msg.h>

int msgget(key_t key, int msgflg);

DESCRIPTION

msgget returns the message queue identifier associated with key.

A message queue identifier and associated message queue and data structure [see intro(2)] are created for key if one of the following are true:

key is IPC_PRIVATE. 

key does not already have a message queue identifier associated with it, and (msgflg&IPC_CREAT) is true. 

On creation, the data structure associated with the new message queue identifier is initialized as follows:

msg_perm.cuid, msg_perm.uid, msg_perm.cgid, and msg_perm.gid are set to the effective user ID and effective group ID, respectively, of the calling process. 

The low-order 9 bits of msg_perm.mode are set to the low-order 9 bits of msgflg.

msg_qnum, msg_lspid, msg_lrpid, msg_stime, and msg_rtime are set to 0. 

msg_ctime is set to the current time. 

msg_qbytes is set to the system limit. 

msgget fails if one or more of the following are true:

EACCES A message queue identifier exists for key, but operation permission [see intro(2)] as specified by the low-order 9 bits of msgflg would not be granted. 

ENOENT A message queue identifier does not exist for key and (msgflg&IPC_CREAT) is false. 

ENOSPC A message queue identifier is to be created but the system-imposed limit on the maximum number of allowed message queue identifiers system wide would be exceeded. 

EEXIST A message queue identifier exists for key but (msgflg&IPC_CREAT) and (msgflg&IPC_EXCL) are both true. 

SEE ALSO

intro(2), msgctl(2), msgop(2), stdipc(3C)

DIAGNOSTICS

Upon successful completion, a non-negative integer, namely a message queue identifier, is returned.  Otherwise, a value of −1 is returned and errno is set to indicate the error.