msgget(3p) — Linux manual page

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

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.1‐2017, 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.

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(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)

COPYRIGHT

       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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