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DAEMON(3)		     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 di-
     rectory to the root (/).

     If the argument noclose is zero, daemon() redirects standard  input,  stan-
     dard 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.   How-
     ever,  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 er-
     ror have been closed before the program was run.  Programs  using	daemon()
     should  therefore either call daemon() before opening any files or sockets,
     or verify that any file descriptors obtained have values greater than 2.

     The daemon() function temporarily ignores SIGHUP while calling setsid(2) to
     prevent a parent session group leader's calls to fork(2) and then	_exit(2)
     from prematurely terminating the child process.

FreeBSD ports 15.1		February 27, 2023		       DAEMON(3)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=daemon&sektion=3&manpath=FreeBSD+15.1-RELEASE+and+Ports>

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