使用PHP 5.5安装xdebug

我已经阅读了很多答案,但无法弄清楚为什么xdebug不起作用.

php.ini中:

[xdebug]
zend_extension="/usr/lib/php5/20090626/xdebug.so"

php -v:

PHP 5.5.6-1+debphp.org~precise+2 (cli) (built: Nov 21 2013 14:31:41) 
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2013 Zend Technologies
    with Zend OPcache v7.0.3-dev, Copyright (c) 1999-2013, by Zend Technologies

/usr/lib/php5/20090626/xdebug.so确实存在.php.ini中没有zend优化器.

如果我尝试安装xdebug:

pecl/xdebug is already installed and is the same as the released version 2.2.3
install failed

提前致谢.