msgctl(3p) — Linux manual page

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.1‐2017, 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 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.1‐2017, Section 3.226,
       Message Queue, sys_msg.h(0p)

COPYRIGHT         top

       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                        MSGCTL(3P)

Pages that refer to this page: sys_msg.h(0p)ipcrm(1p)mq_close(3p)mq_getattr(3p)mq_notify(3p)mq_open(3p)mq_receive(3p)mq_setattr(3p)mq_unlink(3p)msgget(3p)msgrcv(3p)msgsnd(3p)