daemon(3) [debian man page]

DAEMON(3)						     Linux Programmer's Manual							 DAEMON(3)

NAME

       daemon - run in the background

SYNOPSIS

       #include <unistd.h>

       int daemon(int nochdir, int noclose);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       daemon(): _BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)

DESCRIPTION

       The  daemon()  function is for programs wishing to detach themselves from the controlling terminal and run in the background as system dae-
       mons.

       If nochdir is zero, daemon() changes the calling 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  suc-
       cess daemon() returns zero.  If an error occurs, daemon() returns -1 and sets errno to any of the errors specified for the fork(2) and set-
       sid(2).

CONFORMING TO

       Not in POSIX.1-2001.  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.

SEE ALSO

       fork(2), setsid(2)

COLOPHON

       This  page is part of release 3.44 of the Linux man-pages project.  A description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.

GNU
								    2009-12-05								 DAEMON(3)

DAEMON(3)						   BSD 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);

DESCRIPTION

     The daemon() function is for programs wishing to detach themselves from the controlling terminal and run in the background as system daemons.

     Unless the argument nochdir is non-zero, daemon() changes the current working directory to the root (/).

     Unless the argument noclose is non-zero, daemon() will redirect standard input, standard output, and standard error to /dev/null.

RETURN VALUES

     The daemon() function returns 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() function may fail and set errno for any of the errors specified for the library functions fork(2) and setsid(2).

SEE ALSO

     fork(2), setsid(2), sigaction(2)

HISTORY

     The daemon() function first appeared in 4.4BSD.

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 program.  This can happen if any of standard input, standard out-
     put, or standard error 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.

BSD
								   June 9, 1993 							       BSD