191 lines
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191 lines
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<title>shmctl</title>
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<basefont size="3"> <a name="shmctl"></a> <a name="tag_03_676"></a><!-- shmctl -->
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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_676_01"></a>NAME</h4>
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<blockquote>shmctl - XSI shared memory control operations</blockquote>
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<h4><a name="tag_03_676_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/shm.h.html">sys/shm.h</a>><br>
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<br>
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int shmctl(int</tt> <i>shmid</i><tt>, int</tt> <i>cmd</i><tt>, struct shmid_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_676_03"></a>DESCRIPTION</h4>
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<blockquote>
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<p>The <i>shmctl</i>() function operates on XSI shared memory (see the Base Definitions volume of IEEE Std 1003.1-2001,
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<a href="../basedefs/xbd_chap03.html#tag_03_340">Section 3.340, Shared Memory Object</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>shmctl</i>() function provides a variety of shared memory control operations as specified by <i>cmd</i>. The following
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values for <i>cmd</i> are available:</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>shmid_ds</b> data structure associated with <i>shmid</i> into the structure
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pointed to by <i>buf</i>. The contents of the structure are defined in <a href=
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"../basedefs/sys/shm.h.html"><i><sys/shm.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>shmid_ds</b> data structure associated with <i>shmid</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>shm_perm.uid
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shm_perm.gid
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shm_perm.mode </tt> Low-order nine bits.
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</pre>
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<p>IPC_SET can only be executed by a process that has an effective user ID equal to either that of a process with appropriate
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privileges or to the value of <i>shm_perm.cuid</i> or <i>shm_perm.uid</i> in the <b>shmid_ds</b> data structure associated with
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<i>shmid</i>.</p>
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</dd>
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<dt>IPC_RMID</dt>
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<dd>Remove the shared memory identifier specified by <i>shmid</i> from the system and destroy the shared memory segment and
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<b>shmid_ds</b> data structure associated with it. IPC_RMID can only be executed by a process that has an effective user ID equal
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to either that of a process with appropriate privileges or to the value of <i>shm_perm.cuid</i> or <i>shm_perm.uid</i> in the
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<b>shmid_ds</b> data structure associated with <i>shmid</i>.</dd>
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</dl>
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</blockquote>
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<h4><a name="tag_03_676_04"></a>RETURN VALUE</h4>
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<blockquote>
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<p>Upon successful completion, <i>shmctl</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_676_05"></a>ERRORS</h4>
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<blockquote>
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<p>The <i>shmctl</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 equal to 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>shmid</i> is not a valid shared memory 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 equal to IPC_RMID or IPC_SET and the effective user ID of the calling process is not equal to that
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of a process with appropriate privileges and it is not equal to the value of <i>shm_perm.cuid</i> or <i>shm_perm.uid</i> in the
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data structure associated with <i>shmid</i>.</dd>
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</dl>
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<p>The <i>shmctl</i>() function may fail if:</p>
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<dl compact>
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<dt>[EOVERFLOW]</dt>
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<dd>The <i>cmd</i> argument is IPC_STAT and the <i>gid</i> or <i>uid</i> value is too large to be stored in the structure pointed
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to by the <i>buf</i> argument.</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_676_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_676_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. Application developers who need to
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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_676_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_676_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_676_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="shmat.html"><i>shmat</i>()</a> , <a href=
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"shmdt.html"><i>shmdt</i>()</a> , <a href="shmget.html"><i>shmget</i>()</a> , <a href="shm_open.html"><i>shm_open</i>()</a> , <a
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href="shm_unlink.html"><i>shm_unlink</i>()</a> , the Base Definitions volume of IEEE Std 1003.1-2001, <a href=
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"../basedefs/sys/shm.h.html"><i><sys/shm.h></i></a></p>
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</blockquote>
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<h4><a name="tag_03_676_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_676_12"></a>Issue 5</h4>
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<blockquote>
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<p>Moved from SHARED MEMORY to BASE.</p>
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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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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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