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

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

       msgctl — XSI message control operations

SYNOPSIS         top

       #include <sys/msg.h>

       int msgctl(int msqid, int cmd, struct msqid_ds *buf);

DESCRIPTION         top

       The msgctl() 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 msgctl() function shall provide message control operations as
       specified by cmd.  The following values for cmd, and the message
       control operations they specify, are:

       IPC_STAT    Place the current value of each member of the msqid_ds
                   data structure associated with msqid into the structure
                   pointed to by buf.  The contents of this structure are
                   defined in <sys/msg.h>.

       IPC_SET     Set the value of the following members of the msqid_ds
                   data structure associated with msqid to the corresponding
                   value found in the structure pointed to by buf:

                       msg_perm.uid
                       msg_perm.gid
                       msg_perm.mode
                       msg_qbytes

                   Also, the msg_ctime timestamp shall be set to the current
                   time, as described in Section 2.7.1, IPC General
                   Description.

                   IPC_SET can only be executed by a process with
                   appropriate privileges or that has an effective user ID
                   equal to the value of msg_perm.cuid or msg_perm.uid in
                   the msqid_ds data structure associated with msqid.  Only
                   a process with appropriate privileges can raise the value
                   of msg_qbytes.

       IPC_RMID    Remove the message queue identifier specified by msqid
                   from the system and destroy the message queue and
                   msqid_ds data structure associated with it. IPC_RMD can
                   only be executed by a process with appropriate privileges
                   or one that has an effective user ID equal to the value
                   of msg_perm.cuid or msg_perm.uid in the msqid_ds data
                   structure associated with msqid.

RETURN VALUE         top

       Upon successful completion, msgctl() shall return 0; otherwise, it
       shall return −1 and set errno to indicate the error.

ERRORS         top

       The msgctl() function shall fail if:

       EACCES The argument cmd is IPC_STAT and the calling process does not
              have read permission; see Section 2.7, XSI Interprocess
              Communication.

       EINVAL The value of msqid is not a valid message queue identifier; or
              the value of cmd is not a valid command.

       EPERM  The argument cmd is IPC_RMID or IPC_SET and the effective user
              ID of the calling process is not equal to that of a process
              with appropriate privileges and it is not equal to the value
              of msg_perm.cuid or msg_perm.uid in the data structure
              associated with msqid.

       EPERM  The argument cmd is IPC_SET, an attempt is being made to
              increase to the value of msg_qbytes, and the effective user ID
              of the calling process does not have appropriate privileges.

       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,
       mq_close(3p), mq_getattr(3p), mq_notify(3p), mq_open(3p),
       mq_receive(3p), mq_send(3p), mq_setattr(3p), mq_unlink(3p),
       msgget(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                          MSGCTL(3P)