📄 msgctl.html
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><html><head><!-- Copyright 1997 The Open Group, All Rights Reserved --><title>msgctl</title></head><body bgcolor=white><center><font size=2>The Single UNIX ® Specification, Version 2<br>Copyright © 1997 The Open Group</font></center><hr size=2 noshade><h4><a name = "tag_000_007_799"> </a>NAME</h4><blockquote>msgctl - message control operations</blockquote><h4><a name = "tag_000_007_800"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="sysmsg.h.html">sys/msg.h</a>>int msgctl(int <i>msqid</i>, int <i>cmd</i>, struct msqid_ds *<i>buf</i>);</code></pre></blockquote><h4><a name = "tag_000_007_801"> </a>DESCRIPTION</h4><blockquote>The<i>msgctl()</i>function provides message control operations as specified by<i>cmd</i>.The following values for<i>cmd</i>,and the message control operations they specify, are:<dl compact><dt>IPC_STAT<dd>Place the current value of each member of the<b>msqid_ds</b>data structure associated with<i>msqid</i>into the structure pointed to by<i>buf</i>.The contents of this structure are defined in<i><a href="sysmsg.h.html"><sys/msg.h></a></i>.<dt>IPC_SET<dd>Set the value of the following members of the<b>msqid_ds</b>data structure associated with<i>msqid</i>to the corresponding value found in the structure pointed to by<i>buf</i>:<pre><code>msg_perm.uidmsg_perm.gidmsg_perm.modemsg_qbytes</code></pre>IPC_SET can only be executed by a process with appropriate privilegesor that has an 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 associated with<i>msqid</i>.Only a process with appropriate privileges can raise the value of<i>msg_qbytes</i>.<dt>IPC_RMID<dd>Remove the message queue identifier specified by<i>msqid</i>from the system and destroy the message queue and<b>msqid_ds</b>data structure associated with it. IPC_RMDcan only be executed by a process with appropriate privilegesor one that has an 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 associated with<i>msqid</i>.</dl></blockquote><h4><a name = "tag_000_007_802"> </a>RETURN VALUE</h4><blockquote>Upon successful completion,<i>msgctl()</i>returns 0. Otherwise, it returns -1 and<i>errno</i>will be set to indicate the error.</blockquote><h4><a name = "tag_000_007_803"> </a>ERRORS</h4><blockquote>The<i>msgctl()</i>function will fail if:<dl compact><dt>[EACCES]<dd>The argument<i>cmd</i>is IPC_STAT and the calling process does not have read permission, see<a href="ipc.html">IPC</a>.<dt>[EINVAL]<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.<dt>[EPERM]<dd>The argument<i>cmd</i>is IPC_RMID or IPC_SETand the effective user ID of thecalling process is not equal to that of a process with appropriateprivileges and it is not equal to the value of<b>msg_perm.cuid</b>or<b>msg_perm.uid</b>in the data structure associated with<i>msqid</i>.<dt>[EPERM]<dd>The argument<i>cmd</i>is IPC_SET, an attempt is being made to increase to the value of<i>msg_qbytes</i>,and the effective user ID of the calling processdoes not have appropriate privileges.</dl></blockquote><h4><a name = "tag_000_007_804"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_007_805"> </a>APPLICATION USAGE</h4><blockquote>The POSIX Realtime Extension defines alternative interfaces for interprocess communication.Application developers who need to use IPC should design theirapplications so that modules using the IPC routines described in<a href="ipc.html">IPC</a>can be easily modified to use the alternative interfaces.</blockquote><h4><a name = "tag_000_007_806"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_007_807"> </a>SEE ALSO</h4><blockquote><i><a href="mq_close.html">mq_close()</a></i>,<i><a href="mq_getattr.html">mq_getattr()</a></i>,<i><a href="mq_notify.html">mq_notify()</a></i>,<i><a href="mq_open.html">mq_open()</a></i>,<i><a href="mq_receive.html">mq_receive()</a></i>,<i><a href="mq_send.html">mq_send()</a></i>,<i><a href="mq_setattr.html">mq_setattr()</a></i>,<i><a href="mq_unlink.html">mq_unlink()</a></i>,<i><a href="msgget.html">msgget()</a></i>,<i><a href="msgrcv.html">msgrcv()</a></i>,<i><a href="msgsnd.html">msgsnd()</a></i>,<i><a href="sysmsg.h.html"><sys/msg.h></a></i>,<a href="ipc.html">IPC</a>.</blockquote><h4>DERIVATION</h4><blockquote>Derived from Issue 2 of the SVID.</blockquote><hr size=2 noshade><center><font size=2>UNIX ® is a registered Trademark of The Open Group.<br>Copyright © 1997 The Open Group<br> [ <a href="../index.html">Main Index</a> | <a href="../xshix.html">XSH</a> | <a href="../xcuix.html">XCU</a> | <a href="../xbdix.html">XBD</a> | <a href="../cursesix.html">XCURSES</a> | <a href="../xnsix.html">XNS</a> ]</font></center><hr size=2 noshade></body></html>⌨️ 快捷键说明
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