PHP配置，php.ini以及覆盖问题

在部署一个cms项目到服务器上的时候，因为cms的模板比较老，服务器上用的php是5.3.3版（大于5.3，可以认为是新的），有些页面会显示“deprecated”类别的错误信息。安全起见要抑制页面中的错误信息输出，于是修改php.ini，发现error_reporting已经设定为Off了，表示错误输出到日志文件而不在页面上显示。但是，页面上有显示错误啊！

Google一番后在SO上发现了解决方案，是因为配置的覆盖问题，cms源代码中会覆盖php.ini的配置。那么改动cms中的error_reporting语句就可以解决问题了，比如：

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

以下是详细的解释，来自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.