[apple/libc.git] / gen / FreeBSD / daemon.3

.\" 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.
.\" 4. 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.
.\"
.\"	@(#)daemon.3	8.1 (Berkeley) 6/9/93
.\" $FreeBSD: src/lib/libc/gen/daemon.3,v 1.15 2007/01/09 00:27:53 imp Exp $
.\"
.Dd June 9, 1993
.Dt DAEMON 3
.Os
.Sh NAME
.Nm daemon
.Nd run in the background
.Sh LIBRARY
.Lb libc
.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.
The
.Xr fork 2
system call is used; see CAVEATS below about the environment after a
.Fn fork
(without a corresponding call to one of the exec routines).
On Mac OS X, the use of this API is discouraged in favor of using
.Xr launchd 8 .
.Pp
Unless the argument
.Fa nochdir
is non-zero,
.Fn daemon
changes the current working directory to the root
.Pq Pa / .
.Pp
Unless the argument
.Fa noclose
is non-zero,
.Fn daemon
will redirect standard input, standard output, and standard error to
.Pa /dev/null .
.Sh RETURN VALUES
.Rv -std daemon
.Sh ERRORS
The
.Fn daemon
function 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 launchd 8 ,
.Xr setsid 2 ,
.Xr sigaction 2
.Sh HISTORY
The
.Fn daemon
function first appeared in
.Bx 4.4 .
.Sh CAVEATS
There are limits to what you can do in the child process.
To be totally safe you should restrict yourself to only
executing async-signal safe operations (see
.Xr sigaction 2 )
until such time
as one of the exec functions is called.
All APIs, including global data symbols, in any framework or library
should be assumed to be unsafe after a 
.Fn fork
unless explicitly documented to be safe or async-signal safe.
If you need to use these frameworks in the child 
process, you must exec.
In this situation it is reasonable to exec yourself.
.Pp
Unless the
.Fa noclose
argument is non-zero,
.Fn daemon
will close the first three file descriptors and redirect 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 either call
.Fn daemon
before opening any files or sockets, or verify that any file
descriptors obtained have values greater than 2.
.Pp
The
.Fn daemon
function temporarily ignores
.Dv SIGHUP
while calling
.Xr setsid 2
to prevent a parent session group leader's calls to
.Xr fork 2
and then
.Xr _exit 2
from prematurely terminating the child process.
Commit	Line	Data
5b2abdfb	1	.\" Copyright (c) 1993
e9ce8d39 A	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.
e9ce8d39 A	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	.\"
5b2abdfb	28	.\" @(#)daemon.3 8.1 (Berkeley) 6/9/93
1f2f436a	29	.\" $FreeBSD: src/lib/libc/gen/daemon.3,v 1.15 2007/01/09 00:27:53 imp Exp $
e9ce8d39	30	.\"
5b2abdfb A	31	.Dd June 9, 1993
5b2abdfb A	32	.Dt DAEMON 3
e9ce8d39 A	33	.Os
e9ce8d39 A	34	.Sh NAME
5b2abdfb A	35	.Nm daemon
5b2abdfb A	36	.Nd run in the background
e9ce8d39 A	37	.Sh LIBRARY
	38	.Lb libc
	39	.Sh SYNOPSIS
5b2abdfb	40	.In stdlib.h
e9ce8d39	41	.Ft int
5b2abdfb	42	.Fn daemon "int nochdir" "int noclose"
e9ce8d39 A	43	.Sh DESCRIPTION
e9ce8d39 A	44	The
5b2abdfb A	45	.Fn daemon
	46	function is for programs wishing to detach themselves from the
	47	controlling terminal and run in the background as system daemons.
5f125488 A	48	The
	49	.Xr fork 2
	50	system call is used; see CAVEATS below about the environment after a
	51	.Fn fork
	52	(without a corresponding call to one of the exec routines).
ad3c9f2a A	53	On Mac OS X, the use of this API is discouraged in favor of using
ad3c9f2a A	54	.Xr launchd 8 .
5b2abdfb A	55	.Pp
	56	Unless the argument
	57	.Fa nochdir
	58	is non-zero,
	59	.Fn daemon
9385eb3d A	60	changes the current working directory to the root
9385eb3d A	61	.Pq Pa / .
5b2abdfb A	62	.Pp
	63	Unless the argument
	64	.Fa noclose
	65	is non-zero,
	66	.Fn daemon
9385eb3d A	67	will redirect standard input, standard output, and standard error to
	68	.Pa /dev/null .
	69	.Sh RETURN VALUES
	70	.Rv -std daemon
e9ce8d39	71	.Sh ERRORS
9385eb3d	72	The
5b2abdfb	73	.Fn daemon
9385eb3d	74	function may fail and set
5b2abdfb	75	.Va errno
9385eb3d	76	for any of the errors specified for the library functions
5b2abdfb A	77	.Xr fork 2
	78	and
	79	.Xr setsid 2 .
e9ce8d39	80	.Sh SEE ALSO
5b2abdfb	81	.Xr fork 2 ,
5f125488	82	.Xr launchd 8 ,
3d9156a7 A	83	.Xr setsid 2 ,
3d9156a7 A	84	.Xr sigaction 2
e9ce8d39 A	85	.Sh HISTORY
e9ce8d39 A	86	The
5b2abdfb	87	.Fn daemon
e9ce8d39 A	88	function first appeared in
e9ce8d39 A	89	.Bx 4.4 .
9385eb3d	90	.Sh CAVEATS
5f125488 A	91	There are limits to what you can do in the child process.
	92	To be totally safe you should restrict yourself to only
	93	executing async-signal safe operations (see
	94	.Xr sigaction 2 )
	95	until such time
	96	as one of the exec functions is called.
	97	All APIs, including global data symbols, in any framework or library
	98	should be assumed to be unsafe after a
	99	.Fn fork
	100	unless explicitly documented to be safe or async-signal safe.
	101	If you need to use these frameworks in the child
	102	process, you must exec.
	103	In this situation it is reasonable to exec yourself.
	104	.Pp
9385eb3d A	105	Unless the
	106	.Fa noclose
	107	argument is non-zero,
	108	.Fn daemon
	109	will close the first three file descriptors and redirect them to
	110	.Pa /dev/null .
	111	Normally, these correspond to standard input, standard output, and
	112	standard error.
	113	However, if any of those file descriptors refer to something else, they
	114	will still be closed, resulting in incorrect behavior of the calling program.
	115	This can happen if any of standard input, standard output, or standard
	116	error have been closed before the program was run.
	117	Programs using
	118	.Fn daemon
	119	should therefore either call
	120	.Fn daemon
	121	before opening any files or sockets, or verify that any file
	122	descriptors obtained have values greater than 2.
3d9156a7 A	123	.Pp
	124	The
	125	.Fn daemon
	126	function temporarily ignores
	127	.Dv SIGHUP
	128	while calling
	129	.Xr setsid 2
	130	to prevent a parent session group leader's calls to
	131	.Xr fork 2
	132	and then
	133	.Xr _exit 2
	134	from prematurely terminating the child process.