use POSIX qw{ setsid getcwd close sysconf _SC_OPEN_MAX };

...

foreach my $i (0 .. openmax()) {
    POSIX::close($i);
}

open(STDIN,  "+>/dev/null");
open(STDOUT, "+>&STDIN");
open(STDERR, "+>&STDIN");

# ignore these signals
for (qw(TSTP TTIN TTOU PIPE POLL STOP CONT CHLD)) {
    $SIG{$_} = 'IGNORE' if (exists $SIG{$_});
}

# handle these signals
for (qw(INT HUP ABRT QUIT TRAP TERM)) {
    $SIG{$_} = 'interrupt' if (exists $SIG{$_});
}

unless (my $pid = fork()) {
    exit if $pid;

    POSIX::setsid;  # set session id
    chdir '/';      # change to root directory
    umask 0;        # clear the file creation mask

    while(1) {
        # do whatever your daemon needs to do ...
    }

}

sub interrupt {
    # do whatever to gracefully shutdown
    ...
    die "$0 terminated successfully.\n";
}