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.TH SETSID "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
.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
\(em create session and set process group ID
.SH SYNOPSIS
.LP
.nf
#include <unistd.h>
.P
pid_t setsid(void);
.fi
.SH DESCRIPTION
The
\fIsetsid\fR()
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"
Upon successful completion,
\fIsetsid\fR()
shall return the value of the new process group ID of the calling
process. Otherwise, it shall return \(mi1 and set
.IR errno
to indicate the error.
.SH ERRORS
The
\fIsetsid\fR()
function shall fail if:
.TP
.BR 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.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
None.
.SH RATIONALE
The
\fIsetsid\fR()
function is similar to the
\fIsetpgrp\fR()
function of System V.
System V, without job control, groups processes into
process groups and creates new process groups via
\fIsetpgrp\fR();
only one process group may be part of a login session.
.P
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 POSIX.1\(hy2008 adds the concept of a
session that is created via
\fIsetsid\fR().
The
\fIsetsid\fR()
function also creates the initial process group contained in the
session. Additional process groups can be created via the
\fIsetpgid\fR()
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\fR()
and have it call
\fIsetsid\fR().
The
\fIfork\fR()
function guarantees that the process ID of the new process does not
match any existing process group ID.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIgetsid\fR\^(\|)",
.IR "\fIsetpgid\fR\^(\|)",
.IR "\fIsetpgrp\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2008,
.IR "\fB<sys_types.h>\fP",
.IR "\fB<unistd.h>\fP"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .

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