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.\" $FreeBSD$ 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 44The 45.Fn daemon 46function is for programs wishing to detach themselves from the 47controlling terminal and run in the background as system daemons. 48.Pp 49Unless the argument 50.Fa nochdir 51is non-zero, 52.Fn daemon 53changes the current working directory to the root 54.Pq Pa / . 55.Pp 56Unless the argument 57.Fa noclose 58is non-zero, 59.Fn daemon 60will redirect standard input, standard output, and standard error to 61.Pa /dev/null . 62.Sh RETURN VALUES 63.Rv -std daemon 64.Sh ERRORS 65The 66.Fn daemon 67function may fail and set 68.Va errno 69for any of the errors specified for the library functions 70.Xr fork 2 71and 72.Xr setsid 2 . 73.Sh SEE ALSO 74.Xr fork 2 , 75.Xr setsid 2 , 76.Xr sigaction 2 77.Sh HISTORY 78The 79.Fn daemon 80function first appeared in 81.Bx 4.4 . 82.Sh CAVEATS 83Unless the 84.Fa noclose 85argument is non-zero, 86.Fn daemon 87will close the first three file descriptors and redirect them to 88.Pa /dev/null . 89Normally, these correspond to standard input, standard output, and 90standard error. 91However, if any of those file descriptors refer to something else, they 92will still be closed, resulting in incorrect behavior of the calling program. 93This can happen if any of standard input, standard output, or standard 94error have been closed before the program was run. 95Programs using 96.Fn daemon 97should therefore either call 98.Fn daemon 99before opening any files or sockets, or verify that any file 100descriptors obtained have values greater than 2. 101.Pp 102The 103.Fn daemon 104function temporarily ignores 105.Dv SIGHUP 106while calling 107.Xr setsid 2 108to prevent a parent session group leader's calls to 109.Xr fork 2 110and then 111.Xr _exit 2 112from prematurely terminating the child process. 113