This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
The msgget() function operates on XSI message queues (see the Base
Definitions volume of POSIX.1‐2008, Section 3.225, Message Queue).
It is unspecified whether this function interoperates with the
realtime interprocess communication facilities defined in Section2.8, Realtime.
The msgget() function shall return the message queue identifier
associated with the argument key.
A message queue identifier, associated message queue, and data
structure (see <sys/msg.h>), shall be created for the argument key if
one of the following is true:
* The argument key is equal to IPC_PRIVATE.
* The argument key does not already have a message queue identifier
associated with it, and (msgflg & IPC_CREAT) is non-zero.
Upon creation, the data structure associated with the new message
queue identifier shall be initialized as follows:
* msg_perm.cuid, msg_perm.uid, msg_perm.cgid, and msg_perm.gid
shall be set to the effective user ID and effective group ID,
respectively, of the calling process.
* The low-order 9 bits of msg_perm.mode shall be set to the low-
order 9 bits of msgflg.
* msg_qnum, msg_lspid, msg_lrpid, msg_stime, and msg_rtime shall be
set to 0.
* msg_ctime shall be set to the current time, as described in
Section 2.7.1, IPC General Description.
* msg_qbytes shall be set to the system limit.
The msgget() function shall fail if:
EACCES A message queue identifier exists for the argument key, but
operation permission as specified by the low-order 9 bits of
msgflg would not be granted; see Section 2.7, XSI InterprocessCommunication.
EEXIST A message queue identifier exists for the argument key but
((msgflg & IPC_CREAT) && (msgflg & IPC_EXCL)) is non-zero.
ENOENT A message queue identifier does not exist for the argument key
and (msgflg & IPC_CREAT) is 0.
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.
The following sections are informative.
The POSIX Realtime Extension defines alternative interfaces for
interprocess communication (IPC). Application developers who need to
use IPC should design their applications so that modules using the
IPC routines described in Section 2.7, XSI Interprocess Communication
can be easily modified to use the alternative interfaces.
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
IEEE/The Open Group 2013 MSGGET(3P)