我在哪里可以更改Xdebug的设置？

phpinfo() shows the path to the configuration: /etc/php5/apache2/conf.d/20-xdebug.ini

But the file contains only a string: zend_extension=xdebug.so

The file usr/lib/php5/20100525/xdebug.so looks like this:

In php.ini, there are no lines containing "xdeb" or "remote_connect"

UP: What I need? The phpinfo() shows that the xdebug.remote_connect_back setting is off. I need to turn it on.

Just fill your /etc/php5/apache2/conf.d/20-xdebug.ini with something like :

zend_extension=xdebug.so
xdebug.remote_enable=1
xdebug.remote_connect_back=1
xdebug.remote_host=localhost
xdebug.remote_port=9000
xdebug.remote_handler=dbgp
xdebug.max_nesting_level=10000
;...

And restart apache. All settings from xdebug are available here