daemon(3) - NetBSD Manual Pages

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DAEMON(3)               NetBSD 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.

     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

     On return 0 indicates success with -1 indicating error.


ERRORS

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


SEE ALSO

     fork(2), setsid(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 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.


BUGS

     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
     been invoked.

NetBSD 5.2                     September 3, 1999                    NetBSD 5.2