run in the background
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
changes the current working directory to the root
If the argument noclose is
redirects standard input, standard output and standard error to
daemon() returns 0;
otherwise -1 is returned.
daemon() may fail and set
errno for any of the errors specified for the library
functions fork(2) and setsid(2).
daemon() function first appeared in
4.3BSD-Reno libutil and moved to libc in
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.