MSGGET
Section: POSIX Programmer's Manual (3P)
Updated: 2013
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PROLOG
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.
NAME
msgget
--- get the XSI message queue identifier
SYNOPSIS
#include <sys/msg.h>
int msgget(key_t key, int msgflg);
DESCRIPTION
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
Section 2.8,
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.
RETURN VALUE
Upon successful completion,
msgget()
shall return a non-negative integer, namely a message queue identifier.
Otherwise, it shall return -1 and set
errno
to indicate the error.
ERRORS
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 Interprocess Communication.
- 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.
EXAMPLES
None.
APPLICATION USAGE
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.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
Section 2.7,
XSI Interprocess Communication,
Section 2.8,
Realtime,
ftok(),
mq_close(),
mq_getattr(),
mq_notify(),
mq_open(),
mq_receive(),
mq_send(),
mq_setattr(),
mq_unlink(),
msgctl(),
msgrcv(),
msgsnd()
The Base Definitions volume of POSIX.1-2008,
Section 3.225,
Message Queue,
<sys_msg.h>
COPYRIGHT
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
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
Index
- PROLOG
-
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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