MSGGET(2) | System Calls Manual | MSGGET(2)

# NAME

`msgget` — get message queue

# SYNOPSIS

`#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 is a unique integer greater than zero.

A message queue is created if either key is equal to `IPC_PRIVATE`, or key does not have a message queue identifier associated with it, and the `IPC_CREAT` bit is set in msgflg.

If a new message queue is created, the data structure associated with it (the msqid_ds structure, see msgctl(2)) is initialized as follows:

- msg_perm.cuid and msg_perm.uid are set to the effective UID of the calling process.
- msg_perm.gid and msg_perm.cgid are set to the effective GID of the calling process.
- msg_perm.mode is set to the lower 9 bits of msgflg.
- msg_cbytes, msg_qnum, msg_lspid, msg_lrpid, msg_rtime, and msg_stime are set to 0.
- msg_qbytes is set to the system wide maximum value for the number of bytes in a queue (`MSGMNB`).
- msg_ctime is set to the current time.

# RETURN VALUES

Upon successful completion a positive message queue identifier is returned. Otherwise, -1 is returned and the global variable errno is set to indicate the error.

# ERRORS

[`EACCES`]
  A message queue is already associated with key and the caller has no permission to access it.
[`EEXIST`]
  Both `IPC_CREAT` and `IPC_EXCL` are set in msgflg, and a message queue is already associated with key.
[`ENOSPC`]
  A new message queue could not be created because the system limit for the number of message queues has been reached.
[`ENOENT`]
  `IPC_CREAT` was not set in msgflg and no message queue associated with key was found.

# SEE ALSO

msgctl(2), msgrcv(2), msgsnd(2), ftok(3)

# STANDARDS

The `msgget`() function conforms to the X/Open System Interfaces option of IEEE Std 1003.1-2008 (“POSIX.1”).

# HISTORY

Message queues first appeared in AT&T System V Release 1 UNIX and have been available since NetBSD 1.0.

July 18, 2019 | Debian