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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 .

Any typographical or formatting errors that appear

in this page are most likely

to have been introduced during the conversion of the source files to

man page format. To report such errors, see

https://www.kernel.org/doc/man-pages/reporting_bugs.html .