Name
daemon — run in the background
Synopsis
#include <unistd.h>
int
daemon( |
int nochdir, |
int noclose); |
![[Note]](../stylesheet/note.png) |
Note | |||||
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DESCRIPTION
The daemon() function is for
programs wishing to detach themselves from the controlling
terminal and run in the background as system daemons.
If nochdir is
zero, daemon() changes the
process's current working directory to the root directory
("/"); otherwise, the current working directory is left
unchanged.
If noclose is
zero, daemon() redirects
standard input, standard output, and standard error to
/dev/null; otherwise, no
changes are made to these file descriptors.
RETURN VALUE
(This function forks, and if the fork(2) succeeds, the
parent calls _exit(2), so that further
errors are seen by the child only.) On success daemon() returns zero. If an error occurs,
daemon() returns −1 and
sets errno to any of the errors
specified for the fork(2) and setsid(2).
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
| Interface | Attribute | Value |
daemon() |
Thread safety | MT-Safe |
CONFORMING TO
Not in POSIX.1. A similar function appears on the BSDs.
The daemon() function first
appeared in 4.4BSD.
NOTES
The glibc implementation can also return −1 when
/dev/null exists but is not a
character device with the expected major and minor numbers.
In this case, errno need not be
set.
BUGS
The GNU C library implementation of this function was
taken from BSD, and does not employ the double-fork technique
(i.e., fork(2), setsid(2), fork(2)) that is necessary
to ensure that the resulting daemon process is not a session
leader. Instead, the resulting daemon is a session leader. On systems that follow
System V semantics (e.g., Linux), this means that if the
daemon opens a terminal that is not already a controlling
terminal for another session, then that terminal will
inadvertently become the controlling terminal for the
daemon.
COLOPHON
This page is part of release 5.11 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
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Copyright (c) 1993 The Regents of the University of California. All rights reserved. %%%LICENSE_START(BSD_4_CLAUSE_UCB) 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. All advertising materials mentioning features or use of this software must display the following acknowledgement: This product includes software developed by the University of California, Berkeley and its contributors. 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. %%%LICENSE_END (#)daemon.3 8.1 (Berkeley) 6/9/93 Added mentioning of glibc weirdness wrt unistd.h. 5/11/98, Al Viro |