public function umask($mode)
    {
        global $php_errormsg;

        // CONSIDERME:
        // Throw a warning if mode is 0. PHP converts illegal octal numbers to
        // 0 so 0 might not be what the user intended.

        $str_mode = decoct($mode); // Show octal in messages.

        if (false === @umask($mode)) { // FAILED.
            // Add error from php to end of log message. $php_errormsg.
            $msg = "FileSystem::Umask() FAILED. Value $mode. $php_errormsg";
            throw new Exception($msg);
        }
    }