public function onStart(Server $server): void
    {
        $this->fire(ServerEvent::STARTED, $server);

        $this->masterPid = $masterPid = $server->master_pid;
        $rootPath        = $this->config('rootPath');
        $rootPath        = $rootPath ? " (at $rootPath)" : '';

        // save master process id to file.
        ProcessUtil::setTitle(sprintf('%s: master%s', $this->name, $rootPath));

        $this->log("The <comment>master</comment> process success started. (PID:<info>{$masterPid}</info>, pidFile: $this->pidFile)");
    }