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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>vfork</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_010_362"> </a>NAME</h4><blockquote>vfork - create new process; share virtual memory</blockquote><h4><a name = "tag_000_010_363"> </a>SYNOPSIS</h4><blockquote><pre><code>#include <<a href="unistd.h.html">unistd.h</a>>pid_t vfork(void);</code></pre></blockquote><h4><a name = "tag_000_010_364"> </a>DESCRIPTION</h4><blockquote>The<i>vfork()</i>function has the same effect as<i><a href="fork.html">fork()</a></i>,except that the behaviour is undefined if the process created by<i>vfork()</i>either modifies any data other than a variable of type<b>pid_t</b>used to store the return value from<i>vfork()</i>,or returns from the function in which<i>vfork()</i>was called, or calls any other function before successfully calling<i><a href="_exit.html">_exit()</a></i>or one of the<i>exec</i>family of functions.</blockquote><h4><a name = "tag_000_010_365"> </a>RETURN VALUE</h4><blockquote>Upon successful completion,<i>vfork()</i>returns 0 to the child process and returns the process ID of the child processto the parent process. Otherwise, -1 is returned to the parent, no childprocess is created, and <i>errno</i> is set to indicate the error.</blockquote><h4><a name = "tag_000_010_366"> </a>ERRORS</h4><blockquote>The<i>vfork()</i>function will fail if:<dl compact><dt>[EAGAIN]<dd>The system-wide limit on the total number of processes under execution wouldbe exceeded, or the system-imposed limit on the total number of processesunder execution by a single user would be exceeded.<dt>[ENOMEM]<dd>There is insufficient swap space for the new process.</dl></blockquote><h4><a name = "tag_000_010_367"> </a>EXAMPLES</h4><blockquote>None.</blockquote><h4><a name = "tag_000_010_368"> </a>APPLICATION USAGE</h4><blockquote>On some systems,<i>vfork()</i>is the same as<i><a href="fork.html">fork()</a></i>.<p>The<i>vfork()</i>function differs from<i><a href="fork.html">fork()</a></i>only in that the child process can share code and data with the callingprocess (parent process). This speeds cloning activity significantly at arisk to the integrity of the parent process if<i>vfork()</i>is misused.<p>The use of<i>vfork()</i>for any purpose except as a prelude to an immediate call to a function fromthe<i>exec</i>family, or to<i><a href="_exit.html">_exit()</a></i>,is not advised.<p>The<i>vfork()</i>function can be used to create new processes without fully copying the addressspace of the old process. If a forked process is simply going to call<i>exec</i>,the data space copied from the parent to the child by<i><a href="fork.html">fork()</a></i>is not used. This is particularly inefficient in a paged environment, making<i>vfork()</i>particularly useful. Depending upon the size of the parent's data space,<i>vfork()</i>can give a significant performance improvement over<i><a href="fork.html">fork()</a></i>.<p>The<i>vfork()</i>function can normally be used just like<i><a href="fork.html">fork()</a></i>.It does not work, however, to return while running in the child's context fromthe caller of<i>vfork()</i>since the eventual return from<i>vfork()</i>would then return to a no longer existent stack frame. Be careful, also, tocall<i><a href="_exit.html">_exit()</a></i>rather than<i><a href="exit.html">exit()</a></i>if you cannot<i>exec</i>,since<i><a href="exit.html">exit()</a></i>flushes and closes standard I/O channels, therebydamaging the parent process' standard I/O data structures. (Even with<i><a href="fork.html">fork()</a></i>,it is wrong to call<i><a href="exit.html">exit()</a></i>,since buffered data would then be flushed twice.)<p>If signal handlers are invoked in the child process after<i>vfork()</i>,they must follow the same rules as other code in the child process.</blockquote><h4><a name = "tag_000_010_369"> </a>FUTURE DIRECTIONS</h4><blockquote>None.</blockquote><h4><a name = "tag_000_010_370"> </a>SEE ALSO</h4><blockquote><i><a href="exec.html">exec</a></i>,<i><a href="exit.html">exit()</a></i>,<i><a href="fork.html">fork()</a></i>,<i><a href="wait.html">wait()</a></i>,<i><a href="unistd.h.html"><unistd.h></a></i>.</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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