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.\" 3. 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.\" $DragonFly: src/lib/libc/gen/daemon.3,v 1.2 2003/06/17 04:26:42 dillon Exp $ 31.\" 32.Dd June 9, 1993 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 to 62.Pa /dev/null . 63.Sh RETURN VALUES 64.Rv -std daemon 65.Sh ERRORS 66The 67.Fn daemon 68function may fail and set 69.Va errno 70for any of the errors specified for the library functions 71.Xr fork 2 72and 73.Xr setsid 2 . 74.Sh SEE ALSO 75.Xr fork 2 , 76.Xr setsid 2 , 77.Xr sigaction 2 78.Sh HISTORY 79The 80.Fn daemon 81function first appeared in 82.Bx 4.4 . 83.Sh CAVEATS 84Unless the 85.Fa 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 95error have been closed before the program was run. 96Programs using 97.Fn daemon 98should therefore either call 99.Fn daemon 100before opening any files or sockets, or verify that any file 101descriptors obtained have values greater than 2. 102.Pp 103The 104.Fn daemon 105function temporarily ignores 106.Dv SIGHUP 107while calling 108.Xr setsid 2 109to prevent a parent session group leader's calls to 110.Xr fork 2 111and then 112.Xr _exit 2 113from prematurely terminating the child process. 114