msgget(2)

NAME

msgget − get message queue

SYNTAX

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

int msgget (key, msgflg)
key_t key;
int msgflg;

DESCRIPTION

The msgget system call returns the message queue identifier associated with key.

A message queue identifier and associated message queue and data structure are created for key if one of the following are true:

The key is equal to IPC_PRIVATE

The key does not already have a message queue identifier associated with it, and (msgflg & IPC_CREAT) is "true". For further information, see intro(.).

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 mgs_rtime are set equal to 0.

The msg_ctime is set equal to the current time.

The msg_qbytes is set equal to the system limit.

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.

DIAGNOSTICS

The msgget system call will fail if one or more of the following are true:

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

[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".

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