Come posso sapere quale webserver un sito web sta utilizzando?


Puoi semplicemente digitare:
wget --save-headers marzorati.co
e otterrai un risultato con queste informazioni:

HTTP/1.1 200 OK
Server: GitHub.com
Content-Type: text/html; charset=utf-8
Last-Modified: Thu, 23 Jul 2015 20:23:09 GMT
Access-Control-Allow-Origin: *
Expires: Thu, 23 Jul 2015 21:14:32 GMT
Cache-Control: max-age=600
Content-Length: 6139
Accept-Ranges: bytes
Date: Thu, 23 Jul 2015 21:04:32 GMT
Via: 1.1 varnish
Age: 0
Connection: keep-alive
X-Served-By: cache-lhr6321-LHR
X-Cache: MISS
X-Cache-Hits: 0
X-Timer: S1437685472.532988,VS0,VE105
Vary: Accept-Encoding

O in altri casi più semplici, un risultato simile:

HTTP/1.1 200 OK
Date: Thu, 23 Jul 2015 20:52:02 GMT
Server: Apache
Content-Type: text/html
X-Powered-By: PHP/5.5.9-1ubuntu4.11
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
X-Ants-Machine-Id: php02
X-Ants-Host: nginx01
Set-Cookie: PHPSESSID=9ofov1hcc8fdv2c3h6ubm0l122; path=/
Vary: Accept-Encoding
Set-Cookie: HASH_PHPSESSID=05DEA1665720FA9F0B5F85DFF23A8AB2F87BA2DE; path=/
Content-Length: 129231
Keep-Alive: timeout=15, max=100
Connection: Keep-Alive