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Ref-docs/POSIX/susv3/functions/msgctl.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta name="generator" content="HTML Tidy, see www.w3.org">
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
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<link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 -->
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<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
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<title>msgctl</title>
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</head>
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<body bgcolor="white">
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<script type="text/javascript" language="JavaScript" src="../jscript/codes.js">
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</script>
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<basefont size="3"> <a name="msgctl"></a> <a name="tag_03_393"></a><!-- msgctl -->
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<!--header start-->
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<center><font size="2">The Open Group Base Specifications Issue 6<br>
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IEEE Std 1003.1-2001<br>
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Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
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<!--header end-->
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<hr size="2" noshade>
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<h4><a name="tag_03_393_01"></a>NAME</h4>
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<blockquote>msgctl - XSI message control operations</blockquote>
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<h4><a name="tag_03_393_02"></a>SYNOPSIS</h4>
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<blockquote class="synopsis">
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<div class="box"><code><tt><sup>[<a href="javascript:open_code('XSI')">XSI</a>]</sup> <img src="../images/opt-start.gif" alt=
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"[Option Start]" border="0"> #include <<a href="../basedefs/sys/msg.h.html">sys/msg.h</a>><br>
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<br>
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int msgctl(int</tt> <i>msqid</i><tt>, int</tt> <i>cmd</i><tt>, struct msqid_ds *</tt><i>buf</i><tt>); <img src=
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"../images/opt-end.gif" alt="[Option End]" border="0"></tt></code></div>
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<tt><br>
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</tt></blockquote>
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<h4><a name="tag_03_393_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>msgctl</i>() function operates on XSI message queues (see the Base Definitions volume of IEEE Std 1003.1-2001,
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<a href="../basedefs/xbd_chap03.html#tag_03_224">Section 3.224, Message Queue</a>). It is unspecified whether this function
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interoperates with the realtime interprocess communication facilities defined in <a href=
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"xsh_chap02_08.html#tag_02_08"><i>Realtime</i></a> .</p>
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<p>The <i>msgctl</i>() function shall provide message control operations as specified by <i>cmd</i>. The following values for
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<i>cmd</i>, and the message control operations they specify, are:</p>
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<dl compact>
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<dt>IPC_STAT</dt>
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<dd>Place the current value of each member of the <b>msqid_ds</b> data structure associated with <i>msqid</i> into the structure
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pointed to by <i>buf</i>. The contents of this structure are defined in <a href=
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"../basedefs/sys/msg.h.html"><i><sys/msg.h></i></a>.</dd>
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<dt>IPC_SET</dt>
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<dd>Set the value of the following members of the <b>msqid_ds</b> data structure associated with <i>msqid</i> to the corresponding
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value found in the structure pointed to by <i>buf</i>:
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<pre>
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<tt>msg_perm.uid
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msg_perm.gid
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msg_perm.mode
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msg_qbytes
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</tt>
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</pre>
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<p>IPC_SET can only be executed by a process with appropriate privileges or that has an effective user ID equal to the value of
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<b>msg_perm.cuid</b> or <b>msg_perm.uid</b> in the <b>msqid_ds</b> data structure associated with <i>msqid</i>. Only a process with
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appropriate privileges can raise the value of <b>msg_qbytes</b>.</p>
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</dd>
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<dt>IPC_RMID</dt>
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<dd>Remove the message queue identifier specified by <i>msqid</i> from the system and destroy the message queue and <b>msqid_ds</b>
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data structure associated with it. IPC_RMD can only be executed by a process with appropriate privileges or one that has an
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effective user ID equal to the value of <b>msg_perm.cuid</b> or <b>msg_perm.uid</b> in the <b>msqid_ds</b> data structure
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associated with <i>msqid</i>.</dd>
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</dl>
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</blockquote>
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<h4><a name="tag_03_393_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, <i>msgctl</i>() shall return 0; otherwise, it shall return -1 and set <i>errno</i> to indicate the
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error.</p>
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</blockquote>
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<h4><a name="tag_03_393_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>msgctl</i>() function shall fail if:</p>
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<dl compact>
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<dt>[EACCES]</dt>
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<dd>The argument <i>cmd</i> is IPC_STAT and the calling process does not have read permission; see <a href=
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"xsh_chap02_07.html#tag_02_07"><i>XSI Interprocess Communication</i></a> .</dd>
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<dt>[EINVAL]</dt>
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<dd>The value of <i>msqid</i> is not a valid message queue identifier; or the value of <i>cmd</i> is not a valid command.</dd>
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<dt>[EPERM]</dt>
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<dd>The argument <i>cmd</i> is IPC_RMID or IPC_SET and the effective user ID of the calling process is not equal to that of a
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process with appropriate privileges and it is not equal to the value of <b>msg_perm.cuid</b> or <b>msg_perm.uid</b> in the data
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structure associated with <i>msqid</i>.</dd>
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<dt>[EPERM]</dt>
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<dd>The argument <i>cmd</i> is IPC_SET, an attempt is being made to increase to the value of <b>msg_qbytes</b>, and the effective
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user ID of the calling process does not have appropriate privileges.</dd>
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</dl>
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</blockquote>
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<hr>
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<div class="box"><em>The following sections are informative.</em></div>
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<h4><a name="tag_03_393_06"></a>EXAMPLES</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_393_07"></a>APPLICATION USAGE</h4>
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<blockquote>
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<p>The POSIX Realtime Extension defines alternative interfaces for interprocess communication (IPC). Application developers who
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need to use IPC should design their applications so that modules using the IPC routines described in <a href=
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"xsh_chap02_07.html#tag_02_07"><i>XSI Interprocess Communication</i></a> can be easily modified to use the alternative
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interfaces.</p>
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</blockquote>
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<h4><a name="tag_03_393_08"></a>RATIONALE</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_393_09"></a>FUTURE DIRECTIONS</h4>
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<blockquote>
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<p>None.</p>
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</blockquote>
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<h4><a name="tag_03_393_10"></a>SEE ALSO</h4>
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<blockquote>
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<p><a href="xsh_chap02_07.html#tag_02_07"><i>XSI Interprocess Communication</i></a> , <a href=
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"xsh_chap02_08.html#tag_02_08"><i>Realtime</i></a> , <a href="mq_close.html"><i>mq_close</i>()</a> , <a href=
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"mq_getattr.html"><i>mq_getattr</i>()</a> , <a href="mq_notify.html"><i>mq_notify</i>()</a> , <a href=
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"mq_open.html"><i>mq_open</i>()</a> , <a href="mq_receive.html"><i>mq_receive</i>()</a> , <a href=
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"mq_send.html"><i>mq_send</i>()</a> , <a href="mq_setattr.html"><i>mq_setattr</i>()</a> , <a href=
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"mq_unlink.html"><i>mq_unlink</i>()</a> , <a href="msgget.html"><i>msgget</i>()</a> , <a href="msgrcv.html"><i>msgrcv</i>()</a> ,
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<a href="msgsnd.html"><i>msgsnd</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/sys/msg.h.html"><i><sys/msg.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_393_11"></a>CHANGE HISTORY</h4>
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<blockquote>
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<p>First released in Issue 2. Derived from Issue 2 of the SVID.</p>
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</blockquote>
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<h4><a name="tag_03_393_12"></a>Issue 5</h4>
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<blockquote>
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<p>The note about use of POSIX Realtime Extension IPC routines has been moved from FUTURE DIRECTIONS to a new APPLICATION USAGE
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section.</p>
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</blockquote>
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<div class="box"><em>End of informative text.</em></div>
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<hr>
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<hr size="2" noshade>
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<center><font size="2"><!--footer start-->
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UNIX ® is a registered Trademark of The Open Group.<br>
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POSIX ® is a registered Trademark of The IEEE.<br>
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[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
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"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
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