int
daemon(
int nochdir
, int noclose
)
)
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
.
)
may fail and set
errno
for any of the errors specified for the library functions
fork(2)
and
setsid(2).
)
function first appeared in
4.4BSD.
)
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.
)
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.