SETSID(2) Linux Programmer's Manual SETSID(2)
setsid - creates a session and sets the process group ID
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
(i.e., its session ID is made the same as its process ID). The calling
process also becomes the process group leader of a new process group in
the session (i.e., its process group ID is made the same as its process
The calling process will be the only process in the new process group
and in the new session. The new session has no controlling terminal.
On success, the (new) session ID of the calling process is returned.
On error, (pid_t) -1 is returned, and errno is set to indicate the
EPERM The process group ID of any process equals the PID of the call-
ing process. Thus, in particular, setsid() fails if the calling
process is already a process group leader.
POSIX.1-2001, POSIX.1-2008, SVr4.
A child created via fork(2) inherits its parent's session ID. The ses-
sion ID is preserved across an execve(2).
A process group leader is a process whose process group ID equals its
PID. Disallowing a process group leader from calling setsid() prevents
the possibility that a process group leader places itself in a new ses-
sion while other processes in the process group remain in the original
session; such a scenario would break the strict two-level hierarchy of
sessions and process groups. In order to be sure that setsid() will
succeed, fork(2) and _exit(2), and have the child do setsid().
setsid(1), getsid(2), setpgid(2), setpgrp(2), tcgetsid(3), creden-
This page is part of release 4.04 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
Linux 2015-08-08 SETSID(2)
Man Pages Copyright Respective Owners. Site Copyright (C) 1994 - 2021
All Rights Reserved.