man2/setsid.2

   1 .\" Copyright Michael Haardt (michael@cantor.informatik.rwth-aachen.de)
   2 .\"     Sat Aug 27 20:43:50 MET DST 1994
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  24 .\" Modified Sun Sep 11 19:19:05 1994 <faith@cs.unc.edu>
  25 .\" Modified Mon Mar 25 10:19:00 1996 <aeb@cwi.nl> (merged a few
  26 .\"     tiny changes from a man page by Charles Livingston).
  27 .\" Modified Sun Jul 21 14:45:46 1996 <aeb@cwi.nl>
  28 .\"
  29 .TH SETSID 2 1994-08-27 "Linux" "Linux Programmer's Manual"
  30 .SH NAME
  31 setsid \- creates a session and sets the process group ID
  32 .SH SYNOPSIS
  33 .ad l
  34 .B #include <unistd.h>
  35 .sp
  36 .B pid_t setsid(void);
  37 .br
  38 .ad b
  39 .SH DESCRIPTION
  40 .BR setsid ()
  41 creates a new session if the calling process is not a
  42 process group leader.
  43 The calling process is the leader of the new
  44 session, the process group leader of the new process group, and has no
  45 controlling tty.
  46 The process group ID and session ID of the calling
  47 process are set to the PID of the calling process.
  48 The calling process will be the only process in
  49 this new process group and in this new session.
  50 .SH "RETURN VALUE"
  51 The session ID of the calling process.
  52 .SH ERRORS
  53 On error, \-1 is returned, and
  54 .I errno
  55 is set.
  56 The only error which can happen is
  57 .BR EPERM .
  58 It is returned when the process group ID of any process
  59 equals the PID of the calling process.
  60 Thus, in particular,
  61 .BR setsid ()
  62 fails if the calling process is already a process group leader.
  63 .SH "CONFORMING TO"
  64 SVr4, POSIX.1-2001.
  65 .SH NOTES
  66 A child created via
  67 .BR fork (2)
  68 inherits its parent's session ID.
  69 The session ID is preserved across an
  70 .BR execve (2).
  71
  72 A process group leader is a process with process group ID equal
  73 to its PID.
  74 In order to be sure that
  75 .BR setsid ()
  76 will succeed,
  77 .BR fork (2)
  78 and
  79 .BR _exit (2),
  80 and have the child do
  81 .BR setsid ().
  82 .SH "SEE ALSO"
  83 .BR getsid (2),
  84 .BR setpgid (2),
  85 .BR setpgrp (2),
  86 .BR tcgetsid (3),
  87 .BR credentials (7)