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DAEMON(3) FreeBSD Library Functions Manual DAEMON(3)
NAME
daemon - run in the background
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdlib.h>
int
daemon(int nochdir, int noclose);
int
daemonfd(int chdirfd, int nullfd);
DESCRIPTION
The daemon() function is for programs wishing to detach themselves from
the controlling terminal and run in the background as system daemons.
If the argument nochdir is zero, daemon() changes the current working
directory to the root (/).
If the argument noclose is zero, daemon() redirects standard input,
standard output, and standard error to /dev/null.
The daemonfd() function is equivalent to the daemon() function except
that arguments are the descriptors for the current working directory and
to the descriptor to /dev/null.
If chdirfd is equal to (-1) the current working directory is not changed.
If nullfd is equals to (-1) the redirection of standard input, standard
output, and standard error is not closed.
RETURN VALUES
The daemon() and daemonfd() functions return the value 0 if successful;
otherwise the value -1 is returned and the global variable errno is set
to indicate the error.
ERRORS
The daemon() and daemonfd() function may fail and set errno for any of
the errors specified for the library functions fork(2) open(2), and
setsid(2).
SEE ALSO
fork(2), setsid(2), sigaction(2)
HISTORY
The daemon() function first appeared in 4.4BSD. The daemonfd() function
first appeared in FreeBSD 12.0.
CAVEATS
Unless the noclose argument is non-zero, daemon() will close the first
three file descriptors and redirect them to /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
to prevent a parent session group leader's calls to fork(2) and then
_exit(2) from prematurely terminating the child process.
FreeBSD 14.0-RELEASE-p11 February 27, 2023 FreeBSD 14.0-RELEASE-p11