daemon —
run in the background
#include
<stdlib.h>
int
daemon(
int
nochdir,
int
noclose);
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.
Upon success,
daemon() returns 0; otherwise
-1 is returned.
The function
daemon() may fail and set
errno for any of the errors specified for the
library functions
fork(2) and
setsid(2).
fork(2),
setsid(2)
The
daemon() function first appeared in
4.4BSD.
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.
![[OpenBSD]](/openbsd.gif){kind=small}