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MSGCTL(3P)                 POSIX Programmer's Manual                MSGCTL(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
       msgctl -- XSI message control operations
SYNOPSIS
       #include <sys/msg.h>
       int msgctl(int msqid, int cmd, struct msqid_ds *buf);
DESCRIPTION
       The msgctl() function operates on XSI message queues (see the Base Def-
       initions  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 spec-
       ified 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 Descrip-
                   tion.
                   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
       Upon successful completion, msgctl()  shall  return  0;  otherwise,  it
       shall return -1 and set errno to indicate the error.
ERRORS
       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 Communi-
              cation.
       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
       None.
APPLICATION USAGE
       The POSIX Realtime Extension defines alternative interfaces for  inter-
       process 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,
       mq_close(),   mq_getattr(),   mq_notify(),   mq_open(),   mq_receive(),
       mq_send(), mq_setattr(), mq_unlink(), msgget(), msgrcv(), msgsnd()
       The Base Definitions volume of  POSIX.1-2008,  Section  3.225,  Message
       Queue, <sys_msg.h>
COPYRIGHT
       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 Electri-
       cal  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.ker-
       nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group                  2013                           MSGCTL(3P)