210 lines
8.8 KiB
HTML
210 lines
8.8 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
|
|
<html>
|
|
<head>
|
|
<meta name="generator" content="HTML Tidy, see www.w3.org">
|
|
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
|
|
<link type="text/css" rel="stylesheet" href="style.css"><!-- Generated by The Open Group's rhtm tool v1.2.1 -->
|
|
<!-- Copyright (c) 2001 The Open Group, All Rights Reserved -->
|
|
<title>setpgid</title>
|
|
</head>
|
|
<body bgcolor="white">
|
|
|
|
<basefont size="3"> <a name="setpgid"></a> <a name="tag_03_658"></a><!-- setpgid -->
|
|
<!--header start-->
|
|
<center><font size="2">The Open Group Base Specifications Issue 6<br>
|
|
IEEE Std 1003.1-2001<br>
|
|
Copyright © 2001 The IEEE and The Open Group, All Rights reserved.</font></center>
|
|
|
|
<!--header end-->
|
|
<hr size="2" noshade>
|
|
<h4><a name="tag_03_658_01"></a>NAME</h4>
|
|
|
|
<blockquote>setpgid - set process group ID for job control</blockquote>
|
|
|
|
<h4><a name="tag_03_658_02"></a>SYNOPSIS</h4>
|
|
|
|
<blockquote class="synopsis">
|
|
<p><code><tt>#include <<a href="../basedefs/unistd.h.html">unistd.h</a>><br>
|
|
<br>
|
|
int setpgid(pid_t</tt> <i>pid</i><tt>, pid_t</tt> <i>pgid</i><tt>);<br>
|
|
</tt></code></p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_658_03"></a>DESCRIPTION</h4>
|
|
|
|
<blockquote>
|
|
<p>The <i>setpgid</i>() function shall either join an existing process group or create a new process group within the session of
|
|
the calling process. The process group ID of a session leader shall not change. Upon successful completion, the process group ID of
|
|
the process with a process ID that matches <i>pid</i> shall be set to <i>pgid</i>. As a special case, if <i>pid</i> is 0, the
|
|
process ID of the calling process shall be used. Also, if <i>pgid</i> is 0, the process group ID of the indicated process shall be
|
|
used.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_658_04"></a>RETURN VALUE</h4>
|
|
|
|
<blockquote>
|
|
<p>Upon successful completion, <i>setpgid</i>() shall return 0; otherwise, -1 shall be returned and <i>errno</i> shall be set to
|
|
indicate the error.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_658_05"></a>ERRORS</h4>
|
|
|
|
<blockquote>
|
|
<p>The <i>setpgid</i>() function shall fail if:</p>
|
|
|
|
<dl compact>
|
|
<dt>[EACCES]</dt>
|
|
|
|
<dd>The value of the <i>pid</i> argument matches the process ID of a child process of the calling process and the child process has
|
|
successfully executed one of the <i><a href="../functions/exec.html">exec</a></i> functions.</dd>
|
|
|
|
<dt>[EINVAL]</dt>
|
|
|
|
<dd>The value of the <i>pgid</i> argument is less than 0, or is not a value supported by the implementation.</dd>
|
|
|
|
<dt>[EPERM]</dt>
|
|
|
|
<dd>The process indicated by the <i>pid</i> argument is a session leader.</dd>
|
|
|
|
<dt>[EPERM]</dt>
|
|
|
|
<dd>The value of the <i>pid</i> argument matches the process ID of a child process of the calling process and the child process is
|
|
not in the same session as the calling process.</dd>
|
|
|
|
<dt>[EPERM]</dt>
|
|
|
|
<dd>The value of the <i>pgid</i> argument is valid but does not match the process ID of the process indicated by the <i>pid</i>
|
|
argument and there is no process with a process group ID that matches the value of the <i>pgid</i> argument in the same session as
|
|
the calling process.</dd>
|
|
|
|
<dt>[ESRCH]</dt>
|
|
|
|
<dd>The value of the <i>pid</i> argument does not match the process ID of the calling process or of a child process of the calling
|
|
process.</dd>
|
|
</dl>
|
|
</blockquote>
|
|
|
|
<hr>
|
|
<div class="box"><em>The following sections are informative.</em></div>
|
|
|
|
<h4><a name="tag_03_658_06"></a>EXAMPLES</h4>
|
|
|
|
<blockquote>
|
|
<p>None.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_658_07"></a>APPLICATION USAGE</h4>
|
|
|
|
<blockquote>
|
|
<p>None.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_658_08"></a>RATIONALE</h4>
|
|
|
|
<blockquote>
|
|
<p>The <i>setpgid</i>() function shall group processes together for the purpose of signaling, placement in foreground or
|
|
background, and other job control actions.</p>
|
|
|
|
<p>The <i>setpgid</i>() function is similar to the <a href="../functions/setpgrp.html"><i>setpgrp</i>()</a> function of 4.2 BSD,
|
|
except that 4.2 BSD allowed the specified new process group to assume any value. This presents certain security problems and is
|
|
more flexible than necessary to support job control.</p>
|
|
|
|
<p>To provide tighter security, <i>setpgid</i>() only allows the calling process to join a process group already in use inside its
|
|
session or create a new process group whose process group ID was equal to its process ID.</p>
|
|
|
|
<p>When a job control shell spawns a new job, the processes in the job must be placed into a new process group via
|
|
<i>setpgid</i>(). There are two timing constraints involved in this action:</p>
|
|
|
|
<ol>
|
|
<li>
|
|
<p>The new process must be placed in the new process group before the appropriate program is launched via one of the <i><a href=
|
|
"../functions/exec.html">exec</a></i> functions.</p>
|
|
</li>
|
|
|
|
<li>
|
|
<p>The new process must be placed in the new process group before the shell can correctly send signals to the new process
|
|
group.</p>
|
|
</li>
|
|
</ol>
|
|
|
|
<p>To address these constraints, the following actions are performed. The new processes call <i>setpgid</i>() to alter their own
|
|
process groups after <a href="../functions/fork.html"><i>fork</i>()</a> but before <i><a href=
|
|
"../functions/exec.html">exec</a></i>. This satisfies the first constraint. Under 4.3 BSD, the second constraint is satisfied by
|
|
the synchronization property of <a href="../functions/vfork.html"><i>vfork</i>()</a>; that is, the shell is suspended until the
|
|
child has completed the <i><a href="../functions/exec.html">exec</a></i>, thus ensuring that the child has completed the
|
|
<i>setpgid</i>(). A new version of <a href="../functions/fork.html"><i>fork</i>()</a> with this same synchronization property was
|
|
considered, but it was decided instead to merely allow the parent shell process to adjust the process group of its child processes
|
|
via <i>setpgid</i>(). Both timing constraints are now satisfied by having both the parent shell and the child attempt to adjust the
|
|
process group of the child process; it does not matter which succeeds first.</p>
|
|
|
|
<p>Since it would be confusing to an application to have its process group change after it began executing (that is, after <i><a
|
|
href="../functions/exec.html">exec</a></i>), and because the child process would already have adjusted its process group before
|
|
this, the [EACCES] error was added to disallow this.</p>
|
|
|
|
<p>One non-obvious use of <i>setpgid</i>() is to allow a job control shell to return itself to its original process group (the one
|
|
in effect when the job control shell was executed). A job control shell does this before returning control back to its parent when
|
|
it is terminating or suspending itself as a way of restoring its job control "state" back to what its parent would expect. (Note
|
|
that the original process group of the job control shell typically matches the process group of its parent, but this is not
|
|
necessarily always the case.)</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_658_09"></a>FUTURE DIRECTIONS</h4>
|
|
|
|
<blockquote>
|
|
<p>None.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_658_10"></a>SEE ALSO</h4>
|
|
|
|
<blockquote>
|
|
<p><a href="exec.html"><i><a href="../functions/exec.html">exec</a></i>()</a> , <a href="getpgrp.html"><i>getpgrp</i>()</a> , <a
|
|
href="setsid.html"><i>setsid</i>()</a> , <a href="tcsetpgrp.html"><i>tcsetpgrp</i>()</a> , the Base Definitions volume of
|
|
IEEE Std 1003.1-2001, <a href="../basedefs/sys/types.h.html"><i><sys/types.h></i></a>, <a href=
|
|
"../basedefs/unistd.h.html"><i><unistd.h></i></a></p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_658_11"></a>CHANGE HISTORY</h4>
|
|
|
|
<blockquote>
|
|
<p>First released in Issue 3. Included for alignment with the POSIX.1-1988 standard.</p>
|
|
</blockquote>
|
|
|
|
<h4><a name="tag_03_658_12"></a>Issue 6</h4>
|
|
|
|
<blockquote>
|
|
<p>In the SYNOPSIS, the optional include of the <a href="../basedefs/sys/types.h.html"><i><sys/types.h></i></a> header is
|
|
removed.</p>
|
|
|
|
<p>The following new requirements on POSIX implementations derive from alignment with the Single UNIX Specification:</p>
|
|
|
|
<ul>
|
|
<li>
|
|
<p>The requirement to include <a href="../basedefs/sys/types.h.html"><i><sys/types.h></i></a> has been removed. Although <a
|
|
href="../basedefs/sys/types.h.html"><i><sys/types.h></i></a> was required for conforming implementations of previous POSIX
|
|
specifications, it was not required for UNIX applications.</p>
|
|
</li>
|
|
|
|
<li>
|
|
<p>The <i>setpgid</i>() function is mandatory since _POSIX_JOB_CONTROL is required to be defined in this issue. This is a FIPS
|
|
requirement.</p>
|
|
</li>
|
|
</ul>
|
|
</blockquote>
|
|
|
|
<div class="box"><em>End of informative text.</em></div>
|
|
|
|
<hr>
|
|
<hr size="2" noshade>
|
|
<center><font size="2"><!--footer start-->
|
|
UNIX ® is a registered Trademark of The Open Group.<br>
|
|
POSIX ® is a registered Trademark of The IEEE.<br>
|
|
[ <a href="../mindex.html">Main Index</a> | <a href="../basedefs/contents.html">XBD</a> | <a href=
|
|
"../utilities/contents.html">XCU</a> | <a href="../functions/contents.html">XSH</a> | <a href="../xrat/contents.html">XRAT</a>
|
|
]</font></center>
|
|
|
|
<!--footer end-->
|
|
<hr size="2" noshade>
|
|
</body>
|
|
</html>
|
|
|