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.
The setsid() 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.
The setsid() function shall fail if:
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.
The following sections are informative.
The setsid() function is similar to the setpgrp() function of System
V. System V, without job control, groups processes into process
groups and creates new process groups via setpgrp(); only one process
group may be part of a login session.
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.1‐2008 adds
the concept of a session that is created via setsid(). The setsid()
function also creates the initial process group contained in the
session. Additional process groups can be created via the setpgid()
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 fork() and have it call setsid(). The fork() function
guarantees that the process ID of the new process does not match any
existing process group ID.
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
IEEE/The Open Group 2013 SETSID(3P)