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.\" $OpenBSD: daemon.3,v 1.14 2022/07/30 07:19:30 jsg Exp $
.\"
.\" Copyright (c) 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.Dd $Mdocdate: July 30 2022 $
.Dt DAEMON 3
.Os
.Sh NAME
.Nm daemon
.Nd run in the background
.Sh SYNOPSIS
.In stdlib.h
.Ft int
.Fn daemon "int nochdir" "int noclose"
.Sh DESCRIPTION
The
.Fn daemon
function is for programs wishing to detach themselves from the
controlling terminal and run in the background as system daemons.
.Pp
If the argument
.Fa nochdir
is zero,
.Fn daemon
changes the current working directory to the root
.Pq Pa / .
.Pp
If the argument
.Fa noclose
is zero,
.Fn daemon
redirects standard input, standard output and standard error to
.Pa /dev/null .
.Sh RETURN VALUES
Upon success,
.Fn daemon
returns 0; otherwise \-1 is returned.
.Sh ERRORS
The function
.Fn daemon
may fail and set
.Va errno
for any of the errors specified for the library functions
.Xr fork 2
and
.Xr setsid 2 .
.Sh SEE ALSO
.Xr fork 2 ,
.Xr setsid 2
.Sh HISTORY
The
.Fn daemon
function first appeared in
.Bx 4.3 Reno
libutil and moved to libc in
.Bx 4.4 .
.Sh CAVEATS
If the
.Ar noclose
argument is zero,
.Fn daemon
closes the first three file descriptors and redirects them to
.Pa /dev/null .
Normally, these correspond to standard input, standard output and
standard error.
However, if any of those file descriptors refer to something else they
will still be closed, resulting in incorrect behavior of the calling program.
This can happen if any of standard input, standard output or standard error
have been closed before the program was run.
Programs using
.Fn daemon
should therefore make sure to either call
.Fn daemon
before opening any files or sockets or, alternately, verifying that
any file descriptors obtained have a value greater than 2.
|
