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.
     The fork(2) system call is used; see CAVEATS below about the environment after a fork() (without a corresponding call to one of the exec rou-
     tines).  On Mac OS X, the use of this API is discouraged in favor of using launchd(8).

     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), launchd(8), setsid(2), sigaction(2)

HISTORY

     The daemon() function first appeared in 4.4BSD.

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 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 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.

     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