在部署一個cms項目到服務器上的時候，因為cms的模板比較老，服務器上用的php是5.3.3版（大于5.3，可以認為是新的），有些頁面會顯示“deprecated”類別的錯誤信息。安全起見要抑制頁面中的錯誤信息輸出，于是修改php.ini，發現error_reporting已經設定為Off了，表示錯誤輸出到日志文件而不在頁面上顯示。但是，頁面上有顯示錯誤啊！

Google一番后在SO上發現了解決方案，是因為配置的覆蓋問題，cms源代碼中會覆蓋php.ini的配置。那么改動cms中的error_reporting語句就可以解決問題了，比如：

if ((DEBUG_MODE & 1) == 1)
{
    error_reporting(E_ALL & ~E_DEPRECATED);
}

以下是詳細的解釋，來自Stefano Locati的博客

PHP Configuration, php.ini and overrides

PHP has several places where configuration can be set. While I had an idea of the precedence of those settings, I decided to test them experimentally to be sure of what I am going to say. In particular this post is focused on error_reporting, but the same considerations can hold true for any setting.

So here is a list of those places, from the more global to the more specific. Each setting lower in the list can override a setting that come before.

1. The php.ini configuration file. In case of Ubuntu there are two of them, /etc/php5/apache2/php.ini is the one used for php apache module. It will have a global effect on all virtual hosts.

2. The conf.d directory. Actually not all installations will have this modularized configuration, but in case of Ubuntu is located in /etc/php5/apache2/conf.d for the apache module. Any file added in this directory is going to be added to main php.ini configuration with higher precedence than php.ini. In other words any setting here will override settings in php.ini - I tested adding an error.ini. It will have a global effect on all vitual hosts.

3. Apache virtual host configuration. Generally set in /etc/apache2/sites-available, every virtual host can have different settings. Inside the VirtualHost tag it's possible to include "php_value error_reporting ", where value is the numeric result of the boolean operations on the constants. In this configuration, in fact is not allowed to use the mnemonic constants but only a numeric value. It will affect only a single virtual host. It will override above settings.

4. .htaccess. It's also possible to set configuration values and in particular the error_reporting setting also in .htaccess, with the same syntax described in 3. It will affect only the directory in which .htaccess is located and all subdirectories. It will override above settings, in this case is not necessary to restart apache.

5. Source code. The last place where this setting can be altered is directly in the executed PHP source. If used, will override all previous settings. It can be set calling the function "error_reporting()" or with "ini_set("error_reporting", )". Compile errors could still show, because the script won't be executed in that case.