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
On return 0 indicates success with -1 indicating error.
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
fork(2),
setsid(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 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.
BUGS
daemon() uses
fork() as part of its tty
detachment mechanism. Consequently the process id changes when
daemon() is invoked. Processes employing
daemon() can not be reliably waited upon until
daemon() has been invoked.