Como você está usando light-ipd fast-cgi , basta defini-lo usando bin -ambiente dentro das configurações lighttpd.
## Start an FastCGI server for php (needs the php5-cgi package)
fastcgi.server = ( ".php" =>
((
"bin-path" => "/usr/bin/php-cgi",
"socket" => "/tmp/php.socket",
"max-procs" => 2,
"idle-timeout" => 20,
"bin-environment" => (
"PHP_FCGI_CHILDREN" => "4",
"PHP_FCGI_MAX_REQUESTS" => "10000",
),
"bin-copy-environment" => (
"PATH", "SHELL", "USER"
),
"broken-scriptfilename" => "enable"
))
)