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DAEMON(3) BSD Library Functions Manual DAEMON(3)
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 ter-
minal 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 specified 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 descrip-
tors 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.
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.
BSD September 3, 1999 BSD
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