1.\" $NetBSD: daemon.3,v 1.14 2003/04/16 13:34:36 wiz Exp $ 2.\" 3.\" Copyright (c) 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)daemon.3 8.1 (Berkeley) 6/9/93 35.\" 36.Dd September 3, 1999 37.Dt DAEMON 3 38.Os 39.Sh NAME 40.Nm daemon 41.Nd run in the background 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.In stdlib.h 46.Ft int 47.Fn daemon "int nochdir" "int noclose" 48.Sh DESCRIPTION 49The 50.Fn daemon 51function is for programs wishing to detach themselves from the 52controlling terminal and run in the background as system daemons. 53.Pp 54Unless the argument 55.Fa nochdir 56is non-zero, 57.Fn daemon 58changes the current working directory to the root 59.Pq Pa / . 60.Pp 61Unless the argument 62.Fa noclose 63is non-zero, 64.Fn daemon 65will redirect standard input, standard output and standard error 66to 67.Pa /dev/null . 68.Sh RETURN VALUES 69On return 0 indicates success with \-1 indicating error. 70.Sh ERRORS 71The function 72.Fn daemon 73may fail and set 74.Va errno 75for any of the errors specified for the library functions 76.Xr fork 2 77and 78.Xr setsid 2 . 79.Sh SEE ALSO 80.Xr fork 2 , 81.Xr setsid 2 82.Sh HISTORY 83The 84.Fn daemon 85function first appeared in 86.Bx 4.4 . 87.Sh CAVEATS 88Unless the 89.Ar noclose 90argument is non-zero, 91.Fn daemon 92will close the first three file descriptors and redirect them to 93.Pa /dev/null . 94Normally, these correspond to standard input, standard output and 95standard error. 96However, if any of those file descriptors refer to something else they 97will still be closed, resulting in incorrect behavior of the calling program. 98This can happen if any of standard input, standard output or standard error 99have been closed before the program was run. 100Programs using 101.Fn daemon 102should therefore make sure to either call 103.Fn daemon 104before opening any files or sockets or, alternately, verifying that 105any file descriptors obtained have a value greater than 2. 106.Sh BUGS 107.Fn daemon 108uses 109.Fn fork 110as part of its tty detachment mechanism. 111Consequently the process id changes when 112.Fn daemon 113is invoked. 114Processes employing 115.Fn daemon 116can not be reliably waited upon until 117.Fn daemon 118has been invoked. 119