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setsid.html
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<!-- Creator : groff version 1.22.4 -->
<!-- CreationDate: Wed Jan 29 11:26:19 2020 -->
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta name="generator" content="groff -Thtml, see www.gnu.org">
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<meta name="Content-Style" content="text/css">
<style type="text/css">
p { margin-top: 0; margin-bottom: 0; vertical-align: top }
pre { margin-top: 0; margin-bottom: 0; vertical-align: top }
table { margin-top: 0; margin-bottom: 0; vertical-align: top }
h1 { text-align: center }
</style>
<title>SETSID</title>
</head>
<body>
<h1 align="center">SETSID</h1>
<a href="#NAME">NAME</a><br>
<a href="#SYNOPSIS">SYNOPSIS</a><br>
<a href="#DESCRIPTION">DESCRIPTION</a><br>
<a href="#RETURN VALUE">RETURN VALUE</a><br>
<a href="#ERRORS">ERRORS</a><br>
<a href="#CONFORMING TO">CONFORMING TO</a><br>
<a href="#NOTES">NOTES</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<a href="#COLOPHON">COLOPHON</a><br>
<hr>
<h2>NAME
<a name="NAME"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">setsid -
creates a session and sets the process group ID</p>
<h2>SYNOPSIS
<a name="SYNOPSIS"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>#include
<sys/types.h> <br>
#include <unistd.h></b></p>
<p style="margin-left:11%; margin-top: 1em"><b>pid_t
setsid(void);</b></p>
<h2>DESCRIPTION
<a name="DESCRIPTION"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>setsid</b>()
creates a new session if the calling process is not a
process group leader. The calling process is the leader of
the new session (i.e., its session ID is made the same as
its process ID). The calling process also becomes the
process group leader of a new process group in the session
(i.e., its process group ID is made the same as its process
ID).</p>
<p style="margin-left:11%; margin-top: 1em">The calling
process will be the only process in the new process group
and in the new session.</p>
<p style="margin-left:11%; margin-top: 1em">Initially, the
new session has no controlling terminal. For details of how
a session acquires a controlling terminal, see
<b>credentials</b>(7).</p>
<h2>RETURN VALUE
<a name="RETURN VALUE"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">On success, the
(new) session ID of the calling process is returned. On
error, <i>(pid_t) -1</i> is returned, and <i>errno</i>
is set to indicate the error.</p>
<h2>ERRORS
<a name="ERRORS"></a>
</h2>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="7%">
<p style="margin-top: 1em"><b>EPERM</b></p></td>
<td width="4%"></td>
<td width="78%">
<p style="margin-top: 1em">The process group ID of any
process equals the PID of the calling process. Thus, in
particular, <b>setsid</b>() fails if the calling process is
already a process group leader.</p></td></tr>
</table>
<h2>CONFORMING TO
<a name="CONFORMING TO"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">POSIX.1-2001,
POSIX.1-2008, SVr4.</p>
<h2>NOTES
<a name="NOTES"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">A child created
via <b>fork</b>(2) inherits its parent’s session ID.
The session ID is preserved across an <b>execve</b>(2).</p>
<p style="margin-left:11%; margin-top: 1em">A process group
leader is a process whose process group ID equals its PID.
Disallowing a process group leader from calling
<b>setsid</b>() prevents the possibility that a process
group leader places itself in a new session while other
processes in the process group remain in the original
session; such a scenario would break the strict two-level
hierarchy of sessions and process groups. In order to be
sure that <b>setsid</b>() will succeed, call <b>fork</b>(2)
and have the parent <b>_exit</b>(2), while the child (which
by definition can’t be a process group leader) calls
<b>setsid</b>().</p>
<p style="margin-left:11%; margin-top: 1em">If a session
has a controlling terminal, and the <b>CLOCAL</b> flag for
that terminal is not set, and a terminal hangup occurs, then
the session leader is sent a <b>SIGHUP</b> signal.</p>
<p style="margin-left:11%; margin-top: 1em">If a process
that is a session leader terminates, then a <b>SIGHUP</b>
signal is sent to each process in the foreground process
group of the controlling terminal.</p>
<h2>SEE ALSO
<a name="SEE ALSO"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>setsid</b>(1),
<b>getsid</b>(2), <b>setpgid</b>(2), <b>setpgrp</b>(2),
<b>tcgetsid</b>(3), <b>credentials</b>(7),
<b>sched</b>(7)</p>
<h2>COLOPHON
<a name="COLOPHON"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">This page is
part of release 5.02 of the Linux <i>man-pages</i> project.
A description of the project, information about reporting
bugs, and the latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.</p>
<hr>
</body>
</html>