NAME
daemon —
run in the background
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.
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.
RETURN VALUES
Upon success, daemon() returns 0;
otherwise -1 is returned.
ERRORS
The function daemon() may fail and set
errno for any of the errors specified for the library
functions fork(2) and setsid(2).
SEE ALSO
HISTORY
The daemon() function first appeared in
4.3BSD-Reno libutil and moved to libc in
4.4BSD.
CAVEATS
If the noclose argument is zero,
daemon() closes the first three file descriptors and
redirects 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 output or standard error have been
closed before the program was run. Programs using
daemon() should therefore make sure to either call
daemon() before opening any files or sockets or,
alternately, verifying that any file descriptors obtained have a value
greater than 2.