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DAEMON(3) NetBSD Library Functions Manual DAEMON(3)
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daemon -- run in the background
Standard C Library (libc, -lc)
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.
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.
On return 0 indicates success with -1 indicating error.
The function daemon() may fail and set errno for any of the errors speci-
fied for the library functions fork(2) and setsid(2).
The daemon() function first appeared in 4.4BSD.
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. How-
ever, 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 open-
ing any files or sockets or, alternately, verifying that any file
descriptors obtained have a value greater than 2.
daemon() uses fork() as part of its tty detachment mechanism. Conse-
quently the process id changes when daemon() is invoked. Processes
employing daemon() can not be reliably waited upon until daemon() has
NetBSD 9.0 September 3, 1999 NetBSD 9.0