433 lines
12 KiB
HTML
433 lines
12 KiB
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 http-equiv="Content-Type" content="text/html; charset=utf-8">
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<meta name="Copyright" content="Copyright (c) 2006 by IBM Corporation">
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<title>msgctl()--Perform Message Control Operations</title>
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<!-- Begin Header Records ========================================== -->
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- US Government Users Restricted Rights -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<!-- Change History: -->
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<!-- YYMMDD USERID Change description -->
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<!-- Direct1 SCRIPT J converted by B2H R4.1 (346) (CMS) by V2KEA304 -->
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<!-- at RCHVMW2 on 17 Feb 1999 at 11:05:09 -->
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<!-- Edited by Kersten Jan 02 -->
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<!-- This file has undergone error condition cleanup on 05/01/02 by JET -->
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<link rel="stylesheet" type="text/css" href="../rzahg/ic.css">
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</head>
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<body>
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<!--End Header Records -->
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<!-- Java sync-link -->
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<script type="text/javascript" language="Javascript" src="../rzahg/synch.js">
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</script>
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<a name="Top_Of_Page"></a>
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<h2>msgctl()--Perform Message Control Operations</h2>
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<div class="box" style="width: 80%;">
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<br>
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Syntax<br>
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<pre>
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#include <sys/msg.h>
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int msgctl(int <em>msqid</em>, int <em>cmd</em>, struct msqid_ds <em>*buf</em>);
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</pre>
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<br>
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Service Program Name: QP0ZUSHR<br>
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<!-- iddvc RMBR -->
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<br>
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Default Public Authority: *USE<br>
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<!-- iddvc RMBR -->
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<br>
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Threadsafe: Yes<br>
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<!-- iddvc RMBR -->
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<br>
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</div>
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<p>The <strong>msgctl()</strong> function allows the caller to control
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the message queue specified by the <em>msqid</em> parameter.</p>
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<p>A message queue is controlled by setting the <em>cmd</em> parameter to one of the following values:</p>
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<dl>
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<dt><strong>IPC_RMID (0x00000000)</strong></dt>
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<dd>Remove the message queue identifier <em>msqid</em> from the system and destroy
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any messages on the message queue.
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Any threads that are waiting in <strong>msgsnd()</strong> or <strong>msgrcv()</strong>
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are woken up and <strong>msgsnd()</strong> or <strong>msgrcv()</strong> returns with a
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return value of -1 and <em>errno</em> set to EIDRM.
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<p>The IPC_RMID command can be run only by a thread with appropriate privileges
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or one that has an effective user ID equal to the user ID of the owner or the user ID
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of the creator of the message queue. The
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structure pointed to by <em>*buf</em> is ignored and can be NULL.</p>
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</dd>
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<dt><strong>IPC_SET (0x00000001)</strong></dt>
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<dd>Set the user ID of the owner, the group ID of the owner, the permissions, and the
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maximum number of bytes for the message queue to the values in the
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<samp>msg_perm.uid</samp>, <samp>msg_perm.gid</samp>,
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<samp>msg_perm.mode</samp>, and <samp>msg_qbytes</samp> members of the
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<samp>msqid_ds</samp> data structure pointed to by <em>*buf</em>.
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<p>The IPC_SET command can be run only by a thread with appropriate privileges or one that
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has an effective user ID equal to the user ID of the owner or the user ID
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of the creator of the message queue.</p>
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<p>In addition, only a thread with appropriate privileges can
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increase the maximum number of bytes for the message queue.</p>
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</dd>
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<dt><strong>IPC_STAT (0x00000002)</strong></dt>
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<dd>Store the current value of each member of the
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<samp>msqid_ds</samp> data structure into the
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structure pointed to by <em>*buf</em>. The IPC_STAT command requires
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read permission to the message queue.</dd>
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</dl>
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<br>
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<h3>Parameters</h3>
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<dl>
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<dt><strong>msqid</strong></dt>
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<dd>(Input) Message queue identifier, a positive integer. It is returned by the
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<a href="ipcmsggt.htm">msgget()</a> function and used to identify the message queue on
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which to perform the control operation.
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</dd>
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<dt><strong>cmd</strong></dt>
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<dd>(Input) Command, the control operation to perform on the message queue.
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Valid values are listed above.</dd>
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<dt><strong>buf</strong></dt>
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<dd>(I/O) Pointer to the message queue data structure to be used to get or set
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message queue information.
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<p>The members of the <samp>msqid_ds</samp> structure are as follows:</p>
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<table cellpadding="5">
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<!-- cols="15 85" -->
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<tr>
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<td align="left" valign="top"><em>struct ipc_perm msg_perm</em> </td>
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<td align="left" valign="top">The members of the <samp>ipc_perm</samp> structure
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are as follows:
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<table cellpadding="5">
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<tr>
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<td align="left" valign="top"><em>uid_t uid</em> </td>
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<td align="left" valign="top">The user ID of the owner of the message queue.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>gid_t gid</em> </td>
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<td align="left" valign="top">The group ID of the owner of the message queue.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>uid_t cuid</em> </td>
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<td align="left" valign="top">The user ID of the creator of the message queue.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>gid_t cgid</em> </td>
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<td align="left" valign="top">The group ID of the creator of the message queue.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>mode_t mode</em> </td>
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<td align="left" valign="top">The permissions for the message queue.</td>
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</tr>
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</table>
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</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>msgnum_t msg_qnum</em> </td>
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<td align="left" valign="top">The number of messages currently on the message queue.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>msglen_t msg_qbytes</em> </td>
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<td align="left" valign="top">The maximum number of bytes allowed on the message queue.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>pid_t msg_lspid</em> </td>
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<td align="left" valign="top">The process ID of the last job to send a message
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using <strong>msgsnd()</strong>.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>pid_t msg_lrpid</em> </td>
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<td align="left" valign="top">The process ID of the last job to receive a message
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using <strong>msgrcv()</strong>.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>time_t msg_stime</em> </td>
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<td align="left" valign="top">The time the last job sent a message to the message queue
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using <strong>msgsnd()</strong>.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>time_t msg_rtime</em> </td>
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<td align="left" valign="top">The time the last job received a message from the message queue
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using <strong>msgrcv()</strong>.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>time_t msg_ctime</em> </td>
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<td align="left" valign="top">The time the last job changed the message queue using
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<strong>msgctl()</strong>.</td>
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</tr>
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</table></dd>
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</dl>
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<h3>Authorities</h3>
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<p><strong><a name="TBLAMCTL1">Authorization Required for
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msgctl()</a></strong></p>
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<table border cellpadding="5">
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<!-- cols="60 20 20" -->
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<tr>
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<th align="left" valign="bottom">Object Referred to</th>
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<th align="left" valign="bottom">Authority Required</th>
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<th align="left" valign="bottom">errno</th>
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</tr>
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<tr>
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<td align="left" valign="top">Message queue for which state information is
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retrieved (<em>cmd</em> = IPC_STAT)</td>
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<td align="left" valign="top">Read</td>
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<td align="left" valign="top">EACCES</td>
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</tr>
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<tr>
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<td align="left" valign="top">Message queue for which state information is set
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(<em>cmd</em> = IPC_SET)</td>
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<td align="left" valign="top">See Note</td>
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<td align="left" valign="top">EPERM</td>
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</tr>
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<tr>
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<td align="left" valign="top">Message queue to be removed (<em>cmd</em> =
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IPC_RMID)</td>
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<td align="left" valign="top">See Note</td>
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<td align="left" valign="top">EPERM</td>
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</tr>
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</table>
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<p><strong>Note:</strong> To set message queue information or to remove a
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message queue, the thread must be the owner or creator of the queue, or have
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appropriate privileges. To increase the maximum number of bytes for the message queue,
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a thread must have appropriate privileges.</p>
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<br>
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<h3>Return Value</h3>
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<table cellpadding="5">
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<!-- cols="5 95" -->
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<tr>
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<td align="left" valign="top"><em>0</em></td>
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<td align="left" valign="top"><strong>msgctl()</strong> was successful.</td>
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</tr>
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<tr>
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<td align="left" valign="top" nowrap><em>-1</em></td>
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<td align="left" valign="top"><strong>msgctl()</strong> was not successful. The
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<em>errno</em> variable is set to indicate the error.</td>
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</tr>
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</table>
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<br>
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<br>
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<h3>Error Conditions</h3>
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<p>If <strong>msgctl()</strong> is not successful, <em>errno</em> usually
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indicates one of the following errors. Under some conditions, <em>errno</em>
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could indicate an error other than those listed here.</p>
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<dl>
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<dt><em>[EACCES]</em></dt>
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<dd>
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<p>Permission denied.</p>
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<p>An attempt was made to access an object in a way forbidden by its object
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access permissions.</p>
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<p>The thread does not have access to the specified file, directory, component,
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or path.</p>
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<p>The <em>cmd</em> parameter is IPC_STAT and the calling thread does not have
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read permission.</p>
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</dd>
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<dt><em>[EDAMAGE]</em></dt>
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<dd>
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<p>A damaged object was encountered.</p>
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<p>A referenced object is damaged. The object cannot be used.</p>
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<p>The message queue has been damaged by a previous message queue
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operation.</p>
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</dd>
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<dt><em>[EFAULT]</em></dt>
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<dd>
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<p>The address used for an argument is not correct.</p>
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<p>In attempting to use an argument in a call, the system detected an address
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that is not valid.</p>
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<p>While attempting to access a parameter passed to this function, the system
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detected an address that is not valid.</p>
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</dd>
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<dt><em>[EINVAL]</em></dt>
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<dd>
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<p>The value specified for the argument is not correct.</p>
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<p>A function was passed incorrect argument values, or an operation was
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attempted on an object and the operation specified is not supported for that
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type of object.</p>
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<p>An argument value is not valid, out of range, or NULL.</p>
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<p>One of the following has occurred:</p>
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<ul>
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<li>The <em>msqid</em> parameter is not a valid message queue identifier.</li>
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<li>The <em>cmd</em> parameter is not a valid command.</li>
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<li>The <em>cmd</em> parameter is IPC_SET and the value of <samp>
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msg_qbytes</samp> exceeds the system limit.</li>
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</ul>
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<br>
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</dd>
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<dt><em>[EPERM]</em></dt>
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<dd>
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<p>Operation not permitted.</p>
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<p>You must have appropriate privileges or be the owner of the object or other
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resource to do the requested operation.</p>
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<p>The <em>cmd</em> parameter is equal to IPC_RMID or IPC_SET and both of the
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following are true:</p>
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<ul>
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<li>the caller does not have the appropriate privileges.</li>
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<li>the effective user ID of the caller is not equal to the user ID of the owner
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or the user ID of the creator of the message queue.</li>
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</ul>
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<p>The <em>cmd</em> parameter is IPC_SET and an attempt is being made to
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increase the maximum number of bytes for the message queue, but the the caller does not have
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appropriate privileges.</p>
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</dd>
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<dt><em>[EUNKNOWN]</em></dt>
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<dd>
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<p>Unknown system state.</p>
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<p>The operation failed because of an unknown system state. See any messages in
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the job log and correct any errors that are indicated, then retry the
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operation.</p>
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</dd>
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</dl>
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<br>
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<h3>Error Messages</h3>
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|
|
|
||
|
|
<p>None.</p>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<h3><a name="USAGE_NOTES">Usage Notes</a></h3>
|
||
|
|
|
||
|
|
<ol>
|
||
|
|
<li>"Appropriate privileges" is defined to be *ALLOBJ special authority. If the
|
||
|
|
user profile under which the thread is running does not have *ALLOBJ special
|
||
|
|
authority, the caller does not have appropriate privileges.</li>
|
||
|
|
</ol>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<h3>Related Information</h3>
|
||
|
|
|
||
|
|
<ul>
|
||
|
|
<li>The <<strong>sys/msg.h</strong>> file (see <a href="unix13.htm">
|
||
|
|
Header Files for UNIX-Type Functions</a>)<br>
|
||
|
|
<br>
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li><a href="unix3a.htm#messagequeue">Message Queues</a> for the current system limits.
|
||
|
|
<br><br></li>
|
||
|
|
|
||
|
|
<li><a href="ipcmsggt.htm">msgget()</a>--Get Message Queue<br>
|
||
|
|
<br>
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li><a href="ipcmsgrc.htm">msgrcv()</a>--Receive Message Operation<br>
|
||
|
|
<br>
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li><a href="ipcmsgsn.htm">msgsnd()</a>--Send Message Operation</li>
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<h3>Example</h3>
|
||
|
|
|
||
|
|
<p>See <a href="../apiref/aboutapis.htm#codedisclaimer">Code disclaimer information</a>
|
||
|
|
for information pertaining to code examples.</p>
|
||
|
|
|
||
|
|
<p>The following example performs a control operation on a message queue:</p>
|
||
|
|
|
||
|
|
<pre>
|
||
|
|
#include <sys/msg.h>
|
||
|
|
|
||
|
|
main() {
|
||
|
|
int msqid = 2;
|
||
|
|
int rc;
|
||
|
|
struct msqid_ds buf;
|
||
|
|
|
||
|
|
rc = msgctl(msqid, IPC_STAT, &buf);
|
||
|
|
}
|
||
|
|
</pre>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<hr>
|
||
|
|
API introduced: V3R6
|
||
|
|
|
||
|
|
<hr>
|
||
|
|
<center>
|
||
|
|
<table cellpadding="2" cellspacing="2">
|
||
|
|
<tr align="center">
|
||
|
|
<td valign="middle" align="center"><a href="#Top_Of_Page">Top</a> | <a href=
|
||
|
|
"unix.htm">UNIX-Type APIs</a> | <a href="aplist.htm">APIs by category</a></td>
|
||
|
|
</tr>
|
||
|
|
</table>
|
||
|
|
</center>
|
||
|
|
</body>
|
||
|
|
</html>
|
||
|
|
|