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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | STANDARDS | HISTORY | NOTES | SEE ALSO | COLOPHON |
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setsid(2) System Calls Manual setsid(2)
setsid - creates a session and sets the process group ID
Standard C library (libc, -lc)
#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.1-2008.
POSIX.1-2001, 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 the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
Linux man-pages 6.15 2025-05-17 setsid(2)
Pages that refer to this page: setsid(1), getsid(2), setpgid(2), syscalls(2), daemon(3), posix_spawn(3), tcgetpgrp(3), credentials(7), pthreads(7), pty(7), sched(7), signal-safety(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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