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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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MSGGET(3P) POSIX Programmer's Manual MSGGET(3P)
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.
msgget — get the XSI message queue identifier
#include <sys/msg.h>
int msgget(key_t key, int msgflg);
The msgget() function operates on XSI message queues (see the
Base Definitions volume of POSIX.1‐2017, Section 3.226, 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.
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.
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.
None.
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.
None.
None.
Section 2.7, XSI Interprocess Communication, Section 2.8,
Realtime, ftok(3p), mq_close(3p), mq_getattr(3p), mq_notify(3p),
mq_open(3p), mq_receive(3p), mq_send(3p), mq_setattr(3p),
mq_unlink(3p), msgctl(3p), msgrcv(3p), msgsnd(3p)
The Base Definitions volume of POSIX.1‐2017, Section 3.226,
Message Queue, sys_msg.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. 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.opengroup.org/unix/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 .
IEEE/The Open Group 2017 MSGGET(3P)
Pages that refer to this page: sys_msg.h(0p), ftok(3p), mq_close(3p), mq_getattr(3p), mq_notify(3p), mq_open(3p), mq_receive(3p), mq_setattr(3p), mq_unlink(3p), msgctl(3p), msgrcv(3p), msgsnd(3p)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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