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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
SETSID(2) Linux Programmer's Manual SETSID(2)
setsid - creates a session and sets the process group ID
#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.
EPERM 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'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'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 4.12 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
https://www.kernel.org/doc/man-pages/.
Linux 2016-10-08 SETSID(2)
Pages that refer to this page: setsid(1), getsid(2), setpgid(2), syscalls(2), daemon(3), tcgetpgrp(3), credentials(7), pthreads(7), pty(7), sched(7), signal-safety(7)