456 lines
14 KiB
HTML
456 lines
14 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>shmctl()-Perform Shared Memory 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 Feb 02 -->
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<!-- This file has undergone html 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>shmctl()--Perform Shared Memory 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/shm.h>
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int shmctl(int <em>shmid</em>, int <em>cmd</em>, struct shmid_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>shmctl()</strong> function allows the caller to control
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the shared memory segment specified by the <em>shmid</em> parameter.</p>
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<p>A shared memory segment is controlled by setting the <em>cmd</em> parameter
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to one of the following values:
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<dl>
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<dt><strong>IPC_RMID (0x00000000)</strong></dt>
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<dd>Remove the shared memory segment identifier <em>shmid</em> from the system and
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destroy the shared memory segment.
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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 shared memory segment. 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 shared memory segment to the values in the
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<samp>shm_perm.uid</samp>, <samp>shm_perm.gid</samp>, and
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<samp>shm_perm.mode</samp> members of the
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<samp>shmid_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 shared memory segment.</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>shmid_ds</samp> data structure into the
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structure pointed to by <em>*buf</em>. The IPC_STAT command requires read
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permission to the shared memory segment.<p></dd>
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<dt><strong>SHM_SIZE (0x00000006)</strong></dt>
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<dd>Set the size of the shared memory segment using the <samp>shm_segsz</samp>
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member of the <samp>shmid_ds</samp> data structure pointed to by
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<em>*buf</em>. This value may be larger or smaller than the current size. This
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command is valid for nonteraspace shared memory segments and for teraspace
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shared memory segments created using the SHM_RESIZE_NP option of the <strong>
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shmget()</strong> function. The maximum size to which a nonteraspace shared memory
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segment may be expanded is 16 773 120 bytes (16 MB minus 4096 bytes).
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The maximum size of a resizeable teraspace shared memory segment is
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268 435 456 bytes (256 MB).
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<br>
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The SHM_SIZE command can be run only by a
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thread with appropriate privileges or a thread that has an effective user ID
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equal to the user ID of the owner or the user ID
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of the creator of the shared memory segment.
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<br>
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If a shared memory segment is resized to a smaller size, other threads using
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the memory that is being removed from the shared memory segment may
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experience memory exceptions when accessing that memory.
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</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>shmid</strong></dt>
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<dd>(Input) Shared memory identifier, a positive integer. It is returned by the
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<a href="ipcshmgt.htm">shmget()</a> function and used to identify the shared memory
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segment on which to perform the control operation.<br>
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<br>
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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 shared memory
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segment. Valid values are listed above.<br>
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<br>
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</dd>
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<dt><strong>buf</strong></dt>
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<dd>(I/O) Pointer to the <samp>shmid_ds</samp> structure to be used to get or
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set shared memory information.
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<p>The members of the <samp>shmid_ds</samp> structure are as follows:</p>
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</dd>
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</dl>
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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 shm_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 segment.</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 segment.</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 segment.</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 segment.</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 segment.</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>size_t shm_segsz</em> </td>
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<td align="left" valign="top">The size of the segment in bytes.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>pid_t shm_lpid</em> </td>
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<td align="left" valign="top">The process ID of the last job to attach or detach
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to the segment using <strong>shmat()</strong> or <strong>shmdt()</strong>.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>pid_t shm_cpid</em> </td>
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<td align="left" valign="top">The process ID of the job that created the segment
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using <strong>shmget()</strong>.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>int shm_nattch</em> </td>
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<td align="left" valign="top">The number of jobs attached to the segment.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>time_t shm_atime</em> </td>
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<td align="left" valign="top">The time the last job attached to the segment
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using <strong>shmat()</strong>.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>time_t shm_dtime</em> </td>
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<td align="left" valign="top">The time the last job detached from the segment
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using <strong>shmdt()</strong>.</td>
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</tr>
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<tr>
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<td align="left" valign="top"><em>time_t shm_ctime</em> </td>
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<td align="left" valign="top">The time the last job changed the segment using
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<strong>shmctl()</strong>.</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>Authorities</h3>
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<p><strong><a name="TBLAHCTL1">Authorization Required for
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shmctl()</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">Shared memory segment for which state information
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is 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">Shared memory segment for which state information
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is set (<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">Shared memory segment to be removed
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(<em>cmd</em> = 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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<tr>
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<td align="left" valign="top">Shared memory segment to be resized
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(<em>cmd</em> = SHM_SIZE)</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 shared memory segment information, to remove a
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shared memory segment, or to resize a shared memory segment, the thread must be
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the owner or creator of the shared memory segment or have appropriate
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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>shmctl()</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>shmctl()</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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<h3>Error Conditions</h3>
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<p>If <strong>shmctl()</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
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does not have read permission to shared memory segment.</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>The shared memory segment has been damaged by a previous shared memory
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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>shmid</em> parameter is not a valid shared memory 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 SHM_SIZE, and the teraspace shared memory
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segment cannot be resized because it was not created by specifying
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SHM_RESIZE_NP on the <em>shmflg</em> parameter of <strong>
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shmget()</strong>.</li>
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<li>The <em>cmd</em> parameter is SHM_SIZE, and the new size is not
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valid for the shared memory segment.</li>
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</ul><br>
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</dd>
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<dt><em>[ENOMEM]</em></dt>
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<dd>
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<p>Storage allocation request failed.</p>
|
||
|
|
|
||
|
|
<p>A function needed to allocate storage, but no storage is available.</p>
|
||
|
|
|
||
|
|
<p>A shared memory identifier segment is to be resized, but the amount of
|
||
|
|
available physical memory is not sufficient to fulfill the request.</p>
|
||
|
|
</dd>
|
||
|
|
|
||
|
|
<dt><em>[EPERM]</em></dt>
|
||
|
|
|
||
|
|
<dd>
|
||
|
|
<p>Operation not permitted.</p>
|
||
|
|
|
||
|
|
<p>You must have appropriate privileges or be the owner of the object or other
|
||
|
|
resource to do the requested operation.</p>
|
||
|
|
|
||
|
|
<p>The <em>cmd</em> parameter is IPC_RMID or IPC_SET and both of the
|
||
|
|
following are true:</p>
|
||
|
|
|
||
|
|
<ul>
|
||
|
|
<li>the calling thread does not have the appropriate privileges.</li>
|
||
|
|
|
||
|
|
<li>the effective user ID of the calling thread is not equal to the user ID
|
||
|
|
of the owner or the user ID of the creator of the shared memory segment.</li>
|
||
|
|
</ul><br>
|
||
|
|
</dd>
|
||
|
|
|
||
|
|
<dt><em>[EUNKNOWN]</em></dt>
|
||
|
|
|
||
|
|
<dd>
|
||
|
|
<p>Unknown system state.</p>
|
||
|
|
|
||
|
|
<p>The operation failed because of an unknown system state. See any messages in
|
||
|
|
the job log and correct any errors that are indicated, then retry the
|
||
|
|
operation.</p>
|
||
|
|
</dd>
|
||
|
|
</dl>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<h3>Error Messages</h3>
|
||
|
|
|
||
|
|
<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 thread does not have appropriate privileges.</li>
|
||
|
|
</ol>
|
||
|
|
|
||
|
|
<br>
|
||
|
|
<h3>Related Information</h3>
|
||
|
|
|
||
|
|
<ul>
|
||
|
|
<li>The <<strong>sys/shm.h</strong>> file (see <a href="unix13.htm">
|
||
|
|
Header Files for UNIX-Type Functions</a>)<br>
|
||
|
|
<br>
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li><a href="ipcshmat.htm">shmat()</a>--Attach Shared Memory Segment to Current
|
||
|
|
Process<br>
|
||
|
|
<br>
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li><a href="ipcshmdt.htm">shmdt()</a>--Detach Shared Memory Segment from
|
||
|
|
Calling Process<br>
|
||
|
|
<br>
|
||
|
|
</li>
|
||
|
|
|
||
|
|
<li><a href="ipcshmgt.htm">shmget()</a>--Get ID of Shared Memory Segment with
|
||
|
|
Key</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>For an example of using this function, see <a href="../apiref/apiexusmem.htm">
|
||
|
|
Using Semaphores and Shared Memory</a> in Examples: APIs.</p>
|
||
|
|
|
||
|
|
<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>
|
||
|
|
|