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DAEMON(3)                BSD Library Functions Manual                DAEMON(3)

NAME
     daemon -- run in the background

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <stdlib.h>

     int
     daemon(int nochdir, int noclose);

DESCRIPTION
     The daemon() function is for programs wishing to detach themselves from the controlling terminal and
     run in the background as system daemons.  On Mac OS X, the use of this API is discouraged in favor of
     using launchd(8).

     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.

RETURN VALUES
     The daemon() function returns the value 0 if successful; otherwise the value -1 is returned and the
     global variable errno is set to indicate the error.

ERRORS
     The daemon() function may fail and set errno for any of the errors specified for the library functions
     fork(2) and setsid(2).

SEE ALSO
     fork(2), setsid(2), sigaction(2)

HISTORY
     The daemon() function first appeared in 4.4BSD.

CAVEATS
     Unless the noclose argument is non-zero, daemon() will close the first three file descriptors and redi-rect redirect
     rect 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 either call daemon() before opening any files or sockets, or verify that any
     file descriptors obtained have values greater than 2.

     The daemon() function temporarily ignores SIGHUP while calling setsid(2) to prevent a parent session
     group leader's calls to fork(2) and then _exit(2) from prematurely terminating the child process.

BSD                              June 9, 1993                              BSD