gen/FreeBSD/daemon.3

   1 .\" Copyright (c) 1993
   2 .\"     The Regents of the University of California.  All rights reserved.
   3 .\"
   4 .\" Redistribution and use in source and binary forms, with or without
   5 .\" modification, are permitted provided that the following conditions
   6 .\" are met:
   7 .\" 1. Redistributions of source code must retain the above copyright
   8 .\"    notice, this list of conditions and the following disclaimer.
   9 .\" 2. Redistributions in binary form must reproduce the above copyright
  10 .\"    notice, this list of conditions and the following disclaimer in the
  11 .\"    documentation and/or other materials provided with the distribution.
  12 .\" 4. Neither the name of the University nor the names of its contributors
  13 .\"    may be used to endorse or promote products derived from this software
  14 .\"    without specific prior written permission.
  15 .\"
  16 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  17 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  18 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  19 .\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  20 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  21 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  22 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  23 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  24 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  25 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  26 .\" SUCH DAMAGE.
  27 .\"
  28 .\"     @(#)daemon.3    8.1 (Berkeley) 6/9/93
  29 .\" $FreeBSD: src/lib/libc/gen/daemon.3,v 1.15 2007/01/09 00:27:53 imp Exp $
  30 .\"
  31 .Dd June 9, 1993
  32 .Dt DAEMON 3
  33 .Os
  34 .Sh NAME
  35 .Nm daemon
  36 .Nd run in the background
  37 .Sh LIBRARY
  38 .Lb libc
  39 .Sh SYNOPSIS
  40 .In stdlib.h
  41 .Ft int
  42 .Fn daemon "int nochdir" "int noclose"
  43 .Sh DESCRIPTION
  44 The
  45 .Fn daemon
  46 function is for programs wishing to detach themselves from the
  47 controlling terminal and run in the background as system daemons.
  48 On Mac OS X, the use of this API is discouraged in favor of using
  49 .Xr launchd 8 .
  50 .Pp
  51 Unless the argument
  52 .Fa nochdir
  53 is non-zero,
  54 .Fn daemon
  55 changes the current working directory to the root
  56 .Pq Pa / .
  57 .Pp
  58 Unless the argument
  59 .Fa noclose
  60 is non-zero,
  61 .Fn daemon
  62 will redirect standard input, standard output, and standard error to
  63 .Pa /dev/null .
  64 .Sh RETURN VALUES
  65 .Rv -std daemon
  66 .Sh ERRORS
  67 The
  68 .Fn daemon
  69 function may fail and set
  70 .Va errno
  71 for any of the errors specified for the library functions
  72 .Xr fork 2
  73 and
  74 .Xr setsid 2 .
  75 .Sh SEE ALSO
  76 .Xr fork 2 ,
  77 .Xr setsid 2 ,
  78 .Xr sigaction 2
  79 .Sh HISTORY
  80 The
  81 .Fn daemon
  82 function first appeared in
  83 .Bx 4.4 .
  84 .Sh CAVEATS
  85 Unless the
  86 .Fa noclose
  87 argument is non-zero,
  88 .Fn daemon
  89 will close the first three file descriptors and redirect them to
  90 .Pa /dev/null .
  91 Normally, these correspond to standard input, standard output, and
  92 standard error.
  93 However, if any of those file descriptors refer to something else, they
  94 will still be closed, resulting in incorrect behavior of the calling program.
  95 This can happen if any of standard input, standard output, or standard
  96 error have been closed before the program was run.
  97 Programs using
  98 .Fn daemon
  99 should therefore either call
 100 .Fn daemon
 101 before opening any files or sockets, or verify that any file
 102 descriptors obtained have values greater than 2.
 103 .Pp
 104 The
 105 .Fn daemon
 106 function temporarily ignores
 107 .Dv SIGHUP
 108 while calling
 109 .Xr setsid 2
 110 to prevent a parent session group leader's calls to
 111 .Xr fork 2
 112 and then
 113 .Xr _exit 2
 114 from prematurely terminating the child process.