PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

MSGGET(3P)                POSIX Programmer's Manual               MSGGET(3P)

PROLOG         top

       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         top

       msgget — get the XSI message queue identifier

SYNOPSIS         top

       #include <sys/msg.h>

       int msgget(key_t key, int msgflg);

DESCRIPTION         top

       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         top

       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         top

       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         top

       None.

APPLICATION USAGE         top

       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         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       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.1‐2008, Section 3.225, Message
       Queue, sys_msg.h(0p)

COPYRIGHT         top

       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 .

IEEE/The Open Group                 2013                          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)