PHP运行于Apache 模块方式
当使用 PHP 作为 Apache 模块时，也可以用 Apache 的配置文件（例如 httpd.conf）和 .htaccess 文件中的指令来修改 PHP 的配置设定。需要有“AllowOverride Options”或“AllowOverride All”权限才可以。
有几个 Apache 指令可以使用户在 Apache 配置文件内部修改 PHP 的配置。哪些指令属于 PHP_INI_ALL，PHP_INI_PERDIR 或 PHP_INI_SYSTEM 中的哪一个，请参考附录中的 php.ini 配置选项列表。
php_value name value
设定指定的值。只能用于 PHP_INI_ALL 或 PHP_INI_PERDIR 类型的指令。要清除先前设定的值，把 value 设为 none。
Note: 不要用 php_value 设定布尔值。应该用 php_flag（见下面）。
php_flag name on|off
用来设定布尔值的配置指令。仅能用于 PHP_INI_ALL 和 PHP_INI_PERDIR 类型的指令。
php_admin_value name value
设定指定的指令的值。不能用于 .htaccess 文件。任何用 php_admin_value 设定的指令都不能被 .htaccess 或 virtualhost 中的指令覆盖。要清除先前设定的值，把 value 设为 none。
php_admin_flag name on|off
用来设定布尔值的配置指令。不能用于 .htaccess 文件。任何用 php_admin_flag 设定的指令都不能被 .htaccess 或 virtualhost 中的指令覆盖。
Example #1 Apache 配置例子
<IfModule mod_php5.c>
php_value include_path ".:/usr/local/lib/php"
php_admin_flag engine on
</IfModule>
<IfModule mod_php4.c>
php_value include_path ".:/usr/local/lib/php"
php_admin_flag engine on
</IfModule>
Caution
PHP 常量不存在于 PHP 之外。例如在 httpd.conf 中不能使用 PHP 常量如 E_ALL 或 E_NOTICE 来设定 error_reporting 指令，因为其无意义，实际等于 0。应该用相应的掩码值来替代。这些常量可以在 php.ini 中使用。
通过 Windows 注册表修改 PHP 配置
在 Windows 下运行 PHP 时，可以用 Windows 注册表以目录为单位来修改配置。配置值存放于注册表项 HKLM\SOFTWARE\PHP\Per Directory Values 下面，子项对应于路径名。例如对于目录 c:\inetpub\wwwroot 的配置值会存放于 HKLM\SOFTWARE\PHP\Per Directory Values\c\inetpub\wwwroot 项下面。其中的设定对于任何位于此目录及其任何子目录的脚本都有效。项中的值的`名称是 PHP 配置指令的名字，值的数据是字符串格式的指令值。值中的 PHP 常量不被解析。不过只有可修改范围是 PHP_INI_USER 的配置值可以用此方法设定，PHP_INI_PERDIR 的值就不行。
其它接口下的 PHP
无论怎样运行 PHP，都可以在脚本中通过 ini_set() 而在运行时修改某个值。更多信息见手册中 ini_set() 的页面。
如果对自己系统中的配置设定及其当前值的完整列表感兴趣，可以运行 phpinfo() 函数并查看其结果的页面。也可以在运行时用 ini_get() 或 get_cfg_var() 取得个别配置指令的值。
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User Contributed Notes 13 notes
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3 Anteaus ?2 years ago
One of the most serious problems here is that it is hard to determine programmatically which of three or more possible configuration methods (php.ini, .user.ini, .htaccess) should be used on any given hosting company's server.
The worst outcome is if an install.php routine attempts to set .htaccess directives on a cgi-mode server, in which case the outcome is usually a '500' crash. Once in that situation the php installation routine cannot be rerun to correct the problem, so you effectively have a hosting lockout situation which can only be corrected by manual intervention.
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-2 contrees.du.reve at gmail dot com ?9 years ago
Being able to put php directives in httpd.conf and have them work on a per-directory or per-vitual host basis is just great. Now there's another aspect which might be worth being aware of:
A php.ini directive put into your apache conf file applies to php when it runs as an apache module (i.e. in a web page), but NOT when it runs as CLI (command-line interface).
Such feature that might be unwanted by an unhappy few, but I guess most will find it useful. As far as I'm concerned, I'm really happy that I can use open_basedir in my httpd.conf file, and it restricts the access of web users and sub-admins of my domain, but it does NOT restrict my own command-line php scripts...
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-3 nick at vistaworks dot net ?4 years ago
On Windows, as the documentation above states, you cannot set max_upload_filesize and post_max_size in the registry, because they are PHP_INI_PERDIR.
Confusingly, however, is the fact that phpinfo() will show your changes if you do add those to the regsitry, as if they were taking effect. However, the upload size is *not* changed, regardless of what phpinfo() reports.
I believe the reading of registry values and override happen 'too late' in the request processing, ie, after the file has already been uploaded and rejected.
In a perfect world, phpinfo() would recognize this and not report the overridden values, which is very confusing.
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-4 Woody/mC ?9 years ago
@ pgl: As the documentation says:
"To clear a previously set value use none as the value."
Works fine for me.
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-6 user at NOSPAM dot example dot com ?5 years ago
PHP Constants will work with php_value; for example: