143 lines
3.9 KiB
Groff
143 lines
3.9 KiB
Groff
.\" Copyright (c) 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)daemon.3 8.1 (Berkeley) 6/9/93
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.\" $FreeBSD$
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.\"
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.Dd December 23, 2017
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.Dt DAEMON 3
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.Os
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.Sh NAME
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.Nm daemon
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.Nd run in the background
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdlib.h
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.Ft int
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.Fn daemon "int nochdir" "int noclose"
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.Ft int
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.Fn daemonfd "int chdirfd" "int nullfd"
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.Sh DESCRIPTION
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The
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.Fn daemon
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function is for programs wishing to detach themselves from the
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controlling terminal and run in the background as system daemons.
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.Pp
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Unless the argument
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.Fa nochdir
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is non-zero,
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.Fn daemon
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changes the current working directory to the root
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.Pq Pa / .
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.Pp
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Unless the argument
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.Fa noclose
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is non-zero,
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.Fn daemon
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will redirect standard input, standard output, and standard error to
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.Pa /dev/null .
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.Pp
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The
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.Fn daemonfd
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function is equivalent to the
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.Fn daemon
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function except that arguments are the descriptors for the current working
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directory and to the descriptor to
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.Pa /dev/null .
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.Pp
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If
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.Fa chdirfd
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is equal to
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.Pq -1
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the current working directory is not changed.
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.Pp
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If
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.Fa nullfd
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is equals to
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.Pq -1
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the redirection of standard input, standard output, and standard error is not
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closed.
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.Sh RETURN VALUES
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.Rv -std daemon daemonfd
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.Sh ERRORS
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The
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.Fn daemon
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and
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.Fn daemonfd
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function may fail and set
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.Va errno
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for any of the errors specified for the library functions
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.Xr fork 2
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.Xr open 2 ,
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and
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.Xr setsid 2 .
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.Sh SEE ALSO
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.Xr fork 2 ,
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.Xr setsid 2 ,
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.Xr sigaction 2
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.Sh HISTORY
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The
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.Fn daemon
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function first appeared in
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.Bx 4.4 .
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The
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.Fn daemonfd
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function first appeared in
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.Fx 12.0 .
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.Sh CAVEATS
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Unless the
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.Fa noclose
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argument is non-zero,
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.Fn daemon
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will close the first three file descriptors and redirect them to
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.Pa /dev/null .
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Normally, these correspond to standard input, standard output, and
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standard error.
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However, if any of those file descriptors refer to something else, they
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will still be closed, resulting in incorrect behavior of the calling program.
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This can happen if any of standard input, standard output, or standard
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error have been closed before the program was run.
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Programs using
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.Fn daemon
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should therefore either call
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.Fn daemon
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before opening any files or sockets, or verify that any file
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descriptors obtained have values greater than 2.
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.Pp
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The
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.Fn daemon
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function temporarily ignores
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.Dv SIGHUP
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while calling
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.Xr setsid 2
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to prevent a parent session group leader's calls to
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.Xr fork 2
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and then
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.Xr _exit 2
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from prematurely terminating the child process.
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