我的代码托管在开源中国得Git库里，想使用Git钩子来实现程序的部署，写了一个程序接受钩子的post的数据，但是不能实现程序的部署。。代码如下：

public function index(){
        $logger = new KLogger(LOG_PATH.'KLogger');

        $web_root_dir = APP_PATH;  // /var/www/site

        if(IS_POST){
            $payload = $_POST;
            $payload = json_decode($payload['hook']);
            $logger->info('data from git post...', $payload); 

            // if (!empty($payload['password'])){
                $command = "cd {$web_root_dir} && git pull";
                $logger->info('enter if .....');
                $result = exec($command);
                $logger->info('command execute result...'.$result); 

            // }
        }

    }

在程序里记录了日志，能接收到post数据，但是命令执行不成功，下面是log的内容：

[2015-05-05 2:07:34.114928] [INFO] data from git post...
    password: '123456'
    push_data: stdClass::__set_state(array(
         'before' => '7a563d4498371a8572a88ff22fb726ac7f8dd467',
         'after' => 'f24b208ddb520b1349fca6a5a0295db516b3982b',
         'ref' => 'refs/heads/master',
         'user_id' => 120469,
         'user_name' => '',
         'repository' => stdClass::__set_state(array(
             'name' => '',
             'url' => '',
             'description' => '',
             'homepage' => '',
        )),
         'commits' => array(
            0 => stdClass::__set_state(array(
                 'id' => 'f24b208ddb520b1349fca6a5a0295db516b3982b',
                 'message' => 'a',
                 'timestamp' => '2015-05-05T02:07:35+08:00',
                 'url' => 'http://git.oschina.net/commit/f24b208ddb520b1349fca6a5a0295db516b3982b',
                 'author' => stdClass::__set_state(array(
                     'name' => '',
                     'email' => '',
                )),
            )),
        ),
         'total_commits_count' => 1,
    ))
[2015-05-05 2:07:34.115142] [INFO] enter if .....
[2015-05-05 2:07:35.482580] [INFO] command execute result...