.\" Copyright Michael Haardt (michael@cantor.informatik.rwth-aachen.de)
.\"     Sat Aug 27 20:43:50 MET DST 1994
.\"
.\" This is free documentation; you can redistribute it and/or
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.\" Modified Sun Sep 11 19:19:05 1994 <faith@cs.unc.edu>
.\" Modified Mon Mar 25 10:19:00 1996 <aeb@cwi.nl> (merged a few
.\"	tiny changes from a man page by Charles Livingston).
.\" Modified Sun Jul 21 14:45:46 1996 <aeb@cwi.nl>
.\"
.TH SETSID 2 2008-12-03 "Linux" "Linux Programmer's Manual"
.SH NAME
setsid \- creates a session and sets the process group ID
.SH SYNOPSIS
.ad l
.B #include <unistd.h>
.sp
.B pid_t setsid(void);
.br
.ad b
.SH DESCRIPTION
.BR setsid ()
creates a new session if the calling process is not a
process group leader.
The calling process is the leader of the new
session, the process group leader of the new process group, and has no
controlling tty.
The process group ID and session ID of the calling
process are set to the PID of the calling process.
The calling process will be the only process in
this new process group and in this new session.
.SH "RETURN VALUE"
On success, the (new) session ID of the calling process is returned.
On error,
.I "(pid_t)\ \-1"
is returned, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EPERM
The process group ID of any process equals the PID of the calling process.
Thus, in particular,
.BR setsid ()
fails if the calling process is already a process group leader.
.SH "CONFORMING TO"
SVr4, POSIX.1-2001.
.SH NOTES
A child created via
.BR fork (2)
inherits its parent's session ID.
The session ID is preserved across an
.BR execve (2).

A process group leader is a process with process group ID equal
to its PID.
In order to be sure that
.BR setsid ()
will succeed,
.BR fork (2)
and
.BR _exit (2),
and have the child do
.BR setsid ().
.SH "SEE ALSO"
.BR getsid (2),
.BR setpgid (2),
.BR setpgrp (2),
.BR tcgetsid (3),
.BR credentials (7)
.SH COLOPHON
This page is part of release 3.44 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.