# apt-get install php5-dev
# pecl install htscanner-1.0.0

add the following to /etc/php5/conf.d/htscanner.ini:

[htscanner]
extension="htscanner.so"

; The configuration file htscanner needs to scan for php_* directives
htscanner.config_file=".htaccess"

; The fallback docroot when htscanner can't determine the current docroot
htscanner.default_docroot="/var/customers/webs/"
htscanner.default_ttl=300

; Stop when an error occured in RINIT (no document root, cannot get path_translated,...)
htscanner.stop_on_error = 0

; Warn when an option cannot be set
htscanner.verbose = 0

You will need to adjust “htscanner.default_docroot” to match your setup.

Restart php-fpm and away you go.