I am testing out some daemon code for a Linux platform. Simple stuff.

The following snippet handles two signals:
INT - close open filehandles and exit
HUP - print a message to a log file

My problem is that I can't seem to access STDOUT, or any file handle that I tie to my log file. It seems that the only descriptor I can get any results from is STDERR.

Here's the code: 

use strict;
use POSIX;

my $die = 0;
my $pid = fork;

die "no fork\n" unless defined($pid);
exit if $pid;

close STDIN;
open(STDOUT, '>>access.log');
open(STDERR, '>>error.log');

POSIX::setsid();
umask(0);

print STDERR "daemon started as pid $$\n";

$SIG{INT} = sub { $die = 1; close STDERR; close STDOUT; };
$SIG{HUP} = sub { print STDOUT "HUP caught\n" };

until ($die) {
    sleep(2);
}

[download]
My problem is (specifically) - the "HUP caught" never gets logged to the STDOUT log file.

If I replace all instances of STDOUT with STDERR - I will see the "HUP caught" message in its respective log file. STDERR works just fine.

If I replace all instances of STDOUT with some other descriptor (LOG) - I still do not see the HUP message.

Adding 'select(STDOUT)' does no good.

So, is STDERR the only available descriptor to a daemon process (surely not) - or am I missing something?
and if I am missing something, what is it?

Thanks,
Jeff 

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
F--F--F--F--F--F--F--F--
(the triplet paradiddle)

In reply to STDOUT and daemon processes by jeffa

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