setsid(2) - Linux manual page (original) (raw)
setsid(2) System Calls Manual setsid(2)
NAME top
setsid - creates a session and sets the process group IDLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <unistd.h>**
**pid_t setsid(void);**DESCRIPTION top
**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)](../man7/credentials.7.html).RETURN VALUE top
On success, the (new) session ID of the calling process is
returned. On error, _(pidt) -1_ is returned, and _[errno](../man3/errno.3.html)_ is set to
indicate the error.ERRORS top
**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.STANDARDS top
POSIX.1-2008.HISTORY top
POSIX.1-2001, SVr4.NOTES top
A child created via [fork(2)](../man2/fork.2.html) inherits its parent's session ID. The
session ID is preserved across an [execve(2)](../man2/execve.2.html).
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)](../man2/fork.2.html) and have the
parent [_exit(2)](../man2/%5Fexit.2.html), 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 top
[setsid(1)](../man1/setsid.1.html), [getsid(2)](../man2/getsid.2.html), [setpgid(2)](../man2/setpgid.2.html), [setpgrp(2)](../man2/setpgrp.2.html), [tcgetsid(3)](../man3/tcgetsid.3.html),
[credentials(7)](../man7/credentials.7.html), [sched(7)](../man7/sched.7.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-07-23 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)