Para instalar, Plesk 11.5 en un solo click, tan solo debe ejecutar 
wget -O – http://autoinstall.plesk.com/one-click-installer | sh
En su consola de comandos.
SOURCE: http://forum.parallels.com/showthread.php?288154-One-Click-Install-and-11-5-29
http://download1.parallels.com/Plesk/Doc/en-US/online/plesk-installation-upgrade-migration-guide/