check for mod_pagespeed

curl -D- http://example.com | grep X-Mod-Pagespeed

shows all zeros if it isn’t installed

if it is installed,

% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 966 0 966 0 0 723 0 –:–:– 0:00:01 –:–:– 1618

or alternately curl -D- http://example.com |less

should show something like:

Date: Fri, 07 Sep 2012 21:51:06 GMT
Server: Apache/2.2.3 (CentOS)
…
X-Mod-Pagespeed: 0.10.22.4-1633

% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 966 0 966 0 0 723 0 –:–:– 0:00:01 –:–:– 1618