sudo apt-get install php5-xcache
sudo service php5-fpm restart

That should install Xcache for you :]

Thanks a lot you made my day :)

On Unbuntu (at least 12.04) this will install xcache v1.3.2 from 2010. Whereas the latest stable release according to page http://xcache.lighttpd.net/ is 3.1.0 Just to let you know. I am trying myself to figure out how to install the latest one.