The squid^[2] Debian package only contains the modular (caching) proxy. Turning it into a filtering server requires installing the additional squidguard package. In addition, squid-cgi provides a querying and administration interface for a Squid proxy.

Vor dem Installieren sollte sichergestellt werden, dass das System seinen eigenen vollständigen Namen feststellen kann: der Befehl hostname -f muss einen vollqualifizierten Namen (einschließlich einer Domain) ergeben. Anderenfalls sollte die Datei /etc/hosts so editiert werden, dass sie den vollständigen Namen des Systems (zum Beispiel arrakis.falcot.com) enthält. Der vollständige Rechnername sollte vom Netz-Administrator bestätigt werden, um mögliche Namenskonflikte zu vermeiden.

Enabling the caching server feature is a simple matter of editing the /etc/squid/squid.conf configuration file and allowing machines from the local network to run queries through the proxy. The following example shows the modifications made by the Falcot Corp administrators:

# INSERT YOUR OWN RULE(S) HERE TO ALLOW ACCESS FROM YOUR CLIENTS
#
include /etc/squid/conf.d/*

# Example rule allowing access from your local networks.
# Adapt localnet in the ACL section to list your (internal) IP networks
# from where browsing should be allowed

acl our_networks src 192.168.1.0/24 192.168.2.0/24
http_access allow our_networks
http_access allow localhost
# And finally deny all other access to this proxy
http_access deny all

squid itself does not perform the filtering; this action is delegated to squidGuard. The former must then be configured to interact with the latter. This involves adding the following directive to the /etc/squid/squid.conf file:

url_rewrite_program /usr/bin/squidGuard -c /etc/squid/squidGuard.conf

The /usr/lib/cgi-bin/squidGuard.cgi CGI program also needs to be installed, using /usr/share/doc/squidguard/examples/squidGuard.cgi.gz as a starting point. Required modifications to this script are the $proxy and $proxymaster variables (the name of the proxy and the administrator's contact email, respectively). The $image and $redirect variables should point to existing images representing the rejection of a query.

The filter is enabled with the service squid reload command. However, since the squidguard package does no filtering by default, it is the administrator's task to define the policy. This can be done by creating the /etc/squid/squidGuard.conf file (using /etc/squidguard/squidGuard.conf.default as template if required).

Die aktive Datenbank muss nach jeder Änderung der Konfigurationsdatei squidGuard (oder einer der Domain- beziehungsweise URL-Listen, die sich auf sie beziehen) mit dem Befehl update-squidguard aktualisiert werden. Die Syntax der Konfigurationsdatei ist auf der folgenden Website dokumentiert: