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diff --git a/man/man2/setsid.2 b/man/man2/setsid.2 new file mode 100644 index 000000000..3ee4e2a66 --- /dev/null +++ b/man/man2/setsid.2 @@ -0,0 +1,100 @@ +.\" Copyright Michael Haardt (michael@cantor.informatik.rwth-aachen.de) +.\" Sat Aug 27 20:43:50 MET DST 1994 +.\" and Copyright (C) 2014, Michael Kerrisk <mtk.manpages@gmail.com> +.\" +.\" SPDX-License-Identifier: GPL-2.0-or-later +.\" +.\" Modified Sun Sep 11 19:19:05 1994 <faith@cs.unc.edu> +.\" Modified Mon Mar 25 10:19:00 1996 <aeb@cwi.nl> (merged a few +.\" tiny changes from a man page by Charles Livingston). +.\" Modified Sun Jul 21 14:45:46 1996 <aeb@cwi.nl> +.\" +.TH setsid 2 (date) "Linux man-pages (unreleased)" +.SH NAME +setsid \- creates a session and sets the process group ID +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.B #include <unistd.h> +.P +.B pid_t setsid(void); +.fi +.SH DESCRIPTION +.BR 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). +.P +The calling process will be the only process in +the new process group and in the new session. +.P +Initially, the new session has no controlling terminal. +For details of how a session acquires a controlling terminal, see +.BR credentials (7). +.SH RETURN VALUE +On success, the (new) session ID of the calling process is returned. +On error, +.I "(pid_t)\ \-1" +is returned, and +.I errno +is set to indicate the error. +.SH ERRORS +.TP +.B EPERM +The process group ID of any process equals the PID of the calling process. +Thus, in particular, +.BR setsid () +fails if the calling process is already a process group leader. +.SH STANDARDS +POSIX.1-2008. +.SH HISTORY +POSIX.1-2001, SVr4. +.SH NOTES +A child created via +.BR fork (2) +inherits its parent's session ID. +The session ID is preserved across an +.BR execve (2). +.P +A process group leader is a process whose process group ID equals its PID. +Disallowing a process group leader from calling +.BR 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 +.BR setsid () +will succeed, call +.BR fork (2) +and have the parent +.BR _exit (2), +while the child (which by definition can't be a process group leader) calls +.BR setsid (). +.P +If a session has a controlling terminal, and the +.B CLOCAL +flag for that terminal is not set, +and a terminal hangup occurs, then the session leader is sent a +.B SIGHUP +signal. +.P +If a process that is a session leader terminates, then a +.B SIGHUP +signal is sent to each process in the foreground +process group of the controlling terminal. +.SH SEE ALSO +.BR setsid (1), +.BR getsid (2), +.BR setpgid (2), +.BR setpgrp (2), +.BR tcgetsid (3), +.BR credentials (7), +.BR sched (7) |