Answer

Check your PHP extensions_directory
You do this by typing the command

php -i | grep extension_dir

you will get a path something like /usr/lib/php/extensions/no-debug-non-zts-20060613.

Another Example

php -i | grep extension_dir
extension_dir => /usr/lib/php5/20090626+lfs => /usr/lib/php5/20090626+lfs