MSGGET(P) POSIX Programmer's Manual MSGGET(P)
msgget - get the XSI message queue identifier
int msgget(key_t key, int msgflg);
The msgget() function operates on XSI message queues (see the Base Definitions volume of
IEEE Std 1003.1-2001, Section 3.224, Message Queue). It is unspecified whether this func-
tion interoperates with the realtime interprocess communication facilities defined in
The msgget() function shall return the message queue identifier associated with the argu-
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 equal 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 equal to the low-order 9 bits of
* msg_qnum, msg_lspid, msg_lrpid, msg_stime, and msg_rtime shall be set equal to 0.
* msg_ctime shall be set equal to the current time.
* msg_qbytes shall be set equal 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 XSI Interpro-
cess 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.
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 XSI Interprocess Communication can be easily
modified to use the alternative interfaces.
XSI Interprocess Communication , Realtime , mq_close() , mq_getattr() , mq_notify() ,
mq_open() , mq_receive() , mq_send() , mq_setattr() , mq_unlink() , msgctl() , msgrcv() ,
msgsnd() , the Base Definitions volume of IEEE Std 1003.1-2001, <sys/msg.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 MSGGET(P)