1.修改CodeIgniter/index.php，添加如下：define(‘ROOTDIR‘,dirname(__FILE__).‘/‘);2.修改CodeIgniter/application/config/config.php,如下：$config[‘log_threshold‘] = 1;$config[‘log_path‘] = ROOTDIR.‘logs/‘;3.修改CodeIgniter/system/core/Common.php，如下：a.找到log_message()方法，将行$_log->write_log($level, $message, $php_error);替换为$_log->appendLog($level, $message, $php_error);b.添加如下方法(该方法根据实际需求情况决定是否需要，此处非必要)    function write_message($message, $fileName = ‘‘)    {            static $_log;            $_log =& load_class(‘Log‘);            $_log->writeLog($message, $fileName);    }    4.修改CodeIgniter/system/libraries/Log.phpa.添加属性protected $_log = ‘‘;b.找到属性$_levels，将行protected $_levels = array(‘ERROR‘ => ‘1‘, ‘DEBUG‘ => ‘2‘,  ‘INFO‘ => ‘3‘, ‘ALL‘ => ‘4‘);替换为// modified by xcg add -1protected $_levels = array(‘ERROR‘ => ‘1‘, ‘DEBUG‘ => ‘2‘,  ‘INFO‘ => ‘3‘, ‘ALL‘ => ‘4‘, ‘NORMAL‘ => ‘-1‘);c.在构造方法 __construct()最后添加如下语句// add by xcgregister_shutdown_function(array(& $this, ‘__writeLog‘));d.添加如下方法// add by xcg for cache logpublic function appendLog($level = ‘error‘, $msg, $php_error = FALSE){if ($this->_enabled === FALSE){return FALSE;}$level = strtoupper($level);if ( ! isset($this->_levels[$level]) OR ($this->_levels[$level] > $this->_threshold)){return FALSE;}$msg = $level.‘ ‘.(($level == ‘INFO‘) ? ‘ -‘ : ‘-‘).‘ ‘.date($this->_date_fmt). ‘  ‘.print_r($msg, true)."\n";$this->_log .= $msg;}// add by xcg for writing log when request terminatedfunction __writeLog()        {            $filepath = $this->_log_path.‘ci-‘.date(‘Y-m-d‘).".log";            if ( ! $fp = @fopen($filepath, FOPEN_WRITE_CREATE))            {                    return FALSE;            }            flock($fp, LOCK_EX);            fwrite($fp, $this->_log);            flock($fp, LOCK_UN);            fclose($fp);            @chmod($filepath, FILE_WRITE_MODE);            return TRUE;        }        // add by xcg for writing log to a special file.function writeLog($message, $fileName = ‘‘)   {       $filepath = !empty($fileName)?$this->_log_path.$fileName:$this->_log_path.‘ci-‘.date(‘Y-m-d‘).".log";               if ( ! $fp = @fopen($filepath, FOPEN_WRITE_CREATE))               {                       return FALSE;               }               $message = date($this->_date_fmt). ‘  ‘.print_r($message, true)."\n";               flock($fp, LOCK_EX);               fwrite($fp, $message);               flock($fp, LOCK_UN);               fclose($fp);               @chmod($filepath, FILE_WRITE_MODE);               return TRUE;   }5.最后，在apache或nginx的web目录下的CodeIgniter项目根目录下新建一个权限为777的logs文件夹