.\" Copyright Michael Haardt (michael@cantor.informatik.rwth-aachen.de) .\" Sat Aug 27 20:43:50 MET DST 1994 .\" and Copyright (C) 2014, Michael Kerrisk .\" .\" %%%LICENSE_START(GPLv2+_DOC_FULL) .\" This is free documentation; you can redistribute it and/or .\" modify it under the terms of the GNU General Public License as .\" published by the Free Software Foundation; either version 2 of .\" the License, or (at your option) any later version. .\" .\" The GNU General Public License's references to "object code" .\" and "executables" are to be interpreted as the output of any .\" document formatting or typesetting system, including .\" intermediate and printed output. .\" .\" This manual is distributed in the hope that it will be useful, .\" but WITHOUT ANY WARRANTY; without even the implied warranty of .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the .\" GNU General Public License for more details. .\" .\" You should have received a copy of the GNU General Public .\" License along with this manual; if not, see .\" . .\" %%%LICENSE_END .\" .\" Modified Sun Sep 11 19:19:05 1994 .\" Modified Mon Mar 25 10:19:00 1996 (merged a few .\" tiny changes from a man page by Charles Livingston). .\" Modified Sun Jul 21 14:45:46 1996 .\" .TH SETSID 2 2017-09-15 "Linux" "Linux Programmer's Manual" .SH NAME setsid \- creates a session and sets the process group ID .SH SYNOPSIS .ad l .B #include .br .B #include .PP .B pid_t setsid(void); .br .ad b .SH DESCRIPTION .BR 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 ID). .PP The calling process will be the only process in the new process group and in the new session. .PP Initially, the new session has no controlling terminal. For details of how a session acquires a controlling terminal, see .BR credentials (7). .SH RETURN VALUE On success, the (new) session ID of the calling process is returned. On error, .I "(pid_t)\ \-1" is returned, and .I errno is set to indicate the error. .SH ERRORS .TP .B EPERM The process group ID of any process equals the PID of the calling process. Thus, in particular, .BR setsid () fails if the calling process is already a process group leader. .SH CONFORMING TO POSIX.1-2001, POSIX.1-2008, SVr4. .SH NOTES A child created via .BR fork (2) inherits its parent's session ID. The session ID is preserved across an .BR execve (2). .PP A process group leader is a process whose process group ID equals its PID. Disallowing a process group leader from calling .BR setsid () prevents the possibility that a process group leader places itself in a new session 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 .BR setsid () will succeed, call .BR fork (2) and have the parent .BR _exit (2), while the child (which by definition can't be a process group leader) calls .BR setsid (). .PP If a session has a controlling terminal, and the .B CLOCAL flag for that terminal is not set, and a terminal hangup occurs, then the session leader is sent a .BR SIGHUP signal. .PP If a process that is a session leader terminates, then a .B SIGHUP signal is sent to each process in the foreground process group of the controlling terminal. .SH SEE ALSO .BR setsid (1), .BR getsid (2), .BR setpgid (2), .BR setpgrp (2), .BR tcgetsid (3), .BR credentials (7), .BR sched (7) .SH COLOPHON This page is part of release 5.04 of the Linux .I man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/.