10-24-2002
I'm not sure why you think fcntl() fits into this. To close an fd you use close().
It is absolutely required that a daemon close fd's 0, 1, and 2. After that, as the lawyers say, "reasonable minds may disagree". In the days when we were limited to 64 fd's, it was reasonable to simply loop invoking close() on them all. If I was to write a daemon, yes I guess that I would use get getconf(_SC_OPEN_MAX) to get the max possible fd and loop invoking close() on every last one. This could be thousands of close() calls that aren't needed, but close() fails very quickly when invoked against a non-open fd.
If they are closing stdin, stdout, and stderr, I would have to say that their stance is reasonable. But I do believe they would have a difficult time producing any language in posix that supports them. The posix standard is on-line and we have a link to it on our home page. Exactly which section do they cite?
It should be very easy to solve your problem though. Can't you change the app server to not leave extra fd's open?
Or if this daemon is called, say, daemonx, just write a program that closes all fd's and then exec()'s daemonx. Call your program pre_daemonx. Have your app server call pre_daemonx.
Is the name "daemonx" hard-coded into an unchangable app server? No problem. Rename "daemonx" to "real.daemonx" and call your program "daemonx".
Whichever path you take here, fixing this should be a 10 minute problem.
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LEARN ABOUT FREEBSD
daemon
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.
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 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 out-
put, 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