The Xdebug extension helps you debugging your script by providing a lot of valuable debug information.

Before you install xdebug you should have PHP5 and Apache2 already working properly. Use the terminal to execute the following steps.

Install the latest version of xdebug in PEAR repository:
```
sudo apt-get install php5-dev php-pear
```
Install xdebug through PECL:

sudo pecl install xdebug

Now, you need to find the path of the compiled module (xdebug.so):

find / -name 'xdebug.so'

Copy the found file-path to use in the next steps.

Now we need to configure xdebug with PHP5, so open the php.ini file (usually you'll find it in /etc/php/apache2/php.ini) use gedit to edit the file:

sudo gedit /etc/php/apache2/php.ini

OR, use the pwerful text editor vim:

sudo vim /etc/php/apache2/php.ini

Add the following lines to the file [Note that the first line should contain the file path found in step number 3]:

zend_extension="/usr/lib/php5/20060613/xdebug.so"
xdebug.remote_enable=1
xdebug.remote_handler=dbgp
xdebug.remote_mode=req
xdebug.remote_host=localhost
xdebug.remote_port=9000

Finally, you need to restart apache for the changes to take effect:

sudo /etc/init.d/apache2 restart

To verify that the extention is loaded and configured correctly, check the phpinfo()

The following line should have been appended to the copyright lines:
with Xdebug v2.0.0, Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, by Derick Rethans

For full xdebug extention information, please read the official documentation at http://xdebug.org/docs/

How to install and configure Xdebug to work with PHP5 on Ubuntu