Modifying File ( php.ini )

PHP stores all kinds of configuration in a file called php.ini.You can find this file in the directory where you installed PHP. Sometimes you will need to modify this file for example to use a PHP extension. I won't explain each and every configuration available just the ones that often need modification or special attention.

Some of the configurations are :
register_globals
error_reporting and display_errors
extension and extension_path
session.save_path
max_execution_time
register_globals

Before PHP 4.2.0 the default value for this configuration is On and after 4.2.0 the default value is Off. The reason for this change is because it is so easy to write insecure code with this value on. So make sure that this value is Off in php.ini.
error_reporting and display_errors

Set the value to error_reporting = E_ALL during development but after production set the value to error_reporting = E_NONE .

The reason to use E_ALL during development is so you can catch most of the nasty bugs in your code. PHP will complain just about any errors you make and spit out all kinds of warning ( for example if you're trying to use an uninitialized variable ).

However, after production you should change the value to E_NONE so PHP will keep quiet even if there's an error in your code. This way the user won't have to see all kinds of PHP error message when running the script.

One important thing to note is that you will also need to set the value of display_erros to On. Even if you set error_reporting = E_ALL you will not get any error message ( no matter how buggy our script is ) unless display_errors is set to On.
extension and extension_path

PHP4 comes with about 51 extensions such as GD library ( for graphics creation and manipulation ), CURL, PostgreSQL support etc. These extensions are not turned on automatically. If you need to use the extension, first you need to specify the location of the extensions and then uncomment the extension you want.

The value of extension_path must be set to the directory where the extension is installed which is PHP_INSTALL_DIR/extensions, with PHP_INSTALL_DIR is the directory where you install PHP. For example I installed PHP in C:\Program Files\Apache Group\Apache2\php so the extensions path is :

extension_path = C:/Program Files/Apache Group/Apache2/php/extensions/

Don't forget to add that last slash or it won't work

After specifying the extension_path you will need to uncomment the extension you want to use. In php.ini a comment is started using a semicolon (;). As an example if you want to use GD library then you must remove the semicolon at the beginning of ;extension=php_gd2.dll to extension=php_gd2.dll
session.save_path

This configuration tells PHP where to save the session data. You will need to set this value to an existing directory or you will not be able to use session. In Windows you can set this value as session.save_path = c:/windows/temp/
max_execution_time

The default value for max_execution_time is 30 ( seconds ). But for some scripts 30 seconds is just not enough to complete it's task. For example a database backup script may need more time to save a huge database.

If you think your script will need extra time to finish the job you can set this to a higher value. For example to set the maximun script execution time to 15 minutes ( 900 seconds ) you can modify the configuration as max_execution_time = 900

PHP have a convenient function to modify PHP configuration in runtime, ini_set(). Setting PHP configuration using this function will not make the effect permanent. It last only until the script ends.

Source : http://www.php-mysql-tutorial.com/