MSGGET(2) — SYSTEM CALLS

NAME

msgget − get message queue

SYNOPSIS

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

int msgget (key, msgflg)
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 equal to IPC_PRIVATE.

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

Upon 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 equal 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 equal to the low-order 9 bits of msgflg.

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

msg_ctime is set equal to the current time.

msg_qbytes is set equal to the system limit.

ERRORS

msgget will fail 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) & ( msgflg & IPC_EXCL) ) is “true”.

RETURN VALUE

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.

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