SETSID
Section: Linux Programmer's Manual (2)
Updated: 2017-09-15
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NAME
setsid - creates a session and sets the process group ID
SYNOPSIS
#include <unistd.h>
pid_t setsid(void);
DESCRIPTION
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).
RETURN VALUE
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.
ERRORS
- 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.
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, SVr4.
NOTES
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.
SEE ALSO
setsid(1),
getsid(2),
setpgid(2),
setpgrp(2),
tcgetsid(3),
credentials(7),
sched(7)
COLOPHON
This page is part of release 4.13 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/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
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