Section (1) setsid

Linux manual pages Section 1  


setsid — run a program in a new session


setsid [options] program [arguments]


setsid runs a program in a new session. The command calls fork(2) if already a process group leader. Otherwise, it executes a program in the current process. This default behavior is possible to override by the −−fork option.


−c, −−ctty

Set the controlling terminal to the current one.

−f, −−fork

Always create a new process.

−w, −−wait

Wait for the execution of the program to end, and return the exit value of this program as the return value of setsid.

−V, −−version

Display version information and exit.

−h, −−help

Display help text and exit.




Rick Sladkey <[email protected]>


The setsid command is part of the util-linux package and is available from

  Rick Sladkey <>
In the public domain.

Section (2) setsid

Linux manual pages Section 2  


setsid — creates a session and sets the process group ID


#include <sys/types.h>

#include <unistd.h>
pid_t setsid( void);  


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).

The calling process will be the only process in the new process group and in the new session.

Initially, the new session has no controlling terminal. For details of how a session acquires a controlling terminal, see credentials(7).


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 error.



The process group ID of any process equals the PID of the calling 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_zsingle_quotesz_s session ID. The session 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 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 setsid() will succeed, call fork(2) and have the parent _exit(2), while the child (which by definition can_zsingle_quotesz_t be a process group leader) calls setsid().

If a session has a controlling terminal, and the CLOCAL flag for that terminal is not set, and a terminal hangup occurs, then the session leader is sent a SIGHUP signal.

If a process that is a session leader terminates, then a SIGHUP signal is sent to each process in the foreground process group of the controlling terminal.


setsid(1), getsid(2), setpgid(2), setpgrp(2), tcgetsid(3), credentials(7), sched(7)


This page is part of release 4.16 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−pages/.

  Copyright Michael Haardt (
    Sat Aug 27 20:43:50 MET DST 1994
and Copyright (C) 2014, Michael Kerrisk <>

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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 <>