1.\" $NetBSD: daemon.3,v 1.15 2003/08/07 16:42:46 agc 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. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)daemon.3 8.1 (Berkeley) 6/9/93 31.\" 32.Dd September 3, 1999 33.Dt DAEMON 3 34.Os 35.Sh NAME 36.Nm daemon 37.Nd run in the background 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In stdlib.h 42.Ft int 43.Fn daemon "int nochdir" "int noclose" 44.Sh DESCRIPTION 45The 46.Fn daemon 47function is for programs wishing to detach themselves from the 48controlling terminal and run in the background as system daemons. 49.Pp 50Unless the argument 51.Fa nochdir 52is non-zero, 53.Fn daemon 54changes the current working directory to the root 55.Pq Pa / . 56.Pp 57Unless the argument 58.Fa noclose 59is non-zero, 60.Fn daemon 61will redirect standard input, standard output and standard error 62to 63.Pa /dev/null . 64.Sh RETURN VALUES 65On return 0 indicates success with \-1 indicating error. 66.Sh ERRORS 67The function 68.Fn daemon 69may fail and set 70.Va errno 71for any of the errors specified for the library functions 72.Xr fork 2 73and 74.Xr setsid 2 . 75.Sh SEE ALSO 76.Xr fork 2 , 77.Xr setsid 2 78.Sh HISTORY 79The 80.Fn daemon 81function first appeared in 82.Bx 4.4 . 83.Sh CAVEATS 84Unless the 85.Ar noclose 86argument is non-zero, 87.Fn daemon 88will close the first three file descriptors and redirect them to 89.Pa /dev/null . 90Normally, these correspond to standard input, standard output and 91standard error. 92However, if any of those file descriptors refer to something else they 93will still be closed, resulting in incorrect behavior of the calling program. 94This can happen if any of standard input, standard output or standard error 95have been closed before the program was run. 96Programs using 97.Fn daemon 98should therefore make sure to either call 99.Fn daemon 100before opening any files or sockets or, alternately, verifying that 101any file descriptors obtained have a value greater than 2. 102.Sh BUGS 103.Fn daemon 104uses 105.Fn fork 106as part of its tty detachment mechanism. 107Consequently the process id changes when 108.Fn daemon 109is invoked. 110Processes employing 111.Fn daemon 112can not be reliably waited upon until 113.Fn daemon 114has been invoked. 115