.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "SETSID" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" setsid 
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.SH NAME
setsid \- create session and set process group ID
.SH SYNOPSIS
.LP
\fB#include <unistd.h>
.br
.sp
pid_t setsid(void);
.br
\fP
.SH DESCRIPTION
.LP
The \fIsetsid\fP() function shall create a new session, if the calling
process is not a process group leader. Upon return the
calling process shall be the session leader of this new session, shall
be the process group leader of a new process group, and
shall have no controlling terminal. The process group ID of the calling
process shall be set equal to the process ID of the calling
process. The calling process shall be the only process in the new
process group and the only process in the new session.
.SH RETURN VALUE
.LP
Upon successful completion, \fIsetsid\fP() shall return the value
of the new process group ID of the calling process.
Otherwise, it shall return (\fBpid_t\fP)-1 and set \fIerrno\fP to
indicate the error.
.SH ERRORS
.LP
The \fIsetsid\fP() function shall fail if:
.TP 7
.B EPERM
The calling process is already a process group leader, or the process
group ID of a process other than the calling process
matches the process ID of the calling process.
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
None.
.SH RATIONALE
.LP
The \fIsetsid\fP() function is similar to the \fIsetpgrp\fP() function
of System V.
System V, without job control, groups processes into process groups
and creates new process groups via \fIsetpgrp\fP(); only one process
group may be part of a login session.
.LP
Job control allows multiple process groups within a login session.
In order to limit job control actions so that they can only
affect processes in the same login session, this volume of IEEE\ Std\ 1003.1-2001
adds the concept of a session that is
created via \fIsetsid\fP(). The \fIsetsid\fP() function also creates
the initial process group contained in the session.
Additional process groups can be created via the \fIsetpgid\fP() function.
A System V
process group would correspond to a POSIX System Interfaces session
containing a single POSIX process group. Note that this
function requires that the calling process not be a process group
leader. The usual way to ensure this is true is to create a new
process with \fIfork\fP() and have it call \fIsetsid\fP(). The \fIfork\fP()
function guarantees that the process ID of the new process does not
match any existing
process group ID.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIgetsid\fP(), \fIsetpgid\fP(), \fIsetpgrp\fP(), the Base Definitions
volume of IEEE\ Std\ 1003.1-2001, \fI<sys/types.h>\fP, \fI<unistd.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .