Features and documentation
SquidGuard comes along with a good online documentation. So please have a look at the SquidGuard website.
You need to adapt the file /etc/squid/squid.conf to include SquidGuard in the running squid process. For Squid version 2.5 and below, this entry looks like:
redirect_program /usr/bin/squidGuard redirect_children 5
With Squid version 2.6 this has changed to
url_rewrite_program /usr/sbin/squidGuard url_rewrite_children 5
The squidGuard packages comes along with a very basic blacklist of webpages sorted in one big category: blacklist. These list is a plain text list which has to be transformed into a Berkeley DB Database bevore squidGuard works. You can do this as root with the command:
squidGuard -c /etc/squidGuard.conf -C all
Afterwards, check the ownership of the created database files in /var/lib/squidGuard/db/blacklist/: squidGuard will silently abort (with an error message in /var/log/squidGuard/squidGuard.log) and your proxy runs without filtering. As squidGuard is started via Squid, the database files should be owned by the user and group of squid. Normally this is user squid and group nogroup (you can check squid.conf for cache_effective_user and cache_effective_group). To be shure everything works as expected, enter:
chown squid:nogroup /var/lib/squidGuard/db/blacklist/*
And now you can (re-) start squid and everything should work as expected. Have a look at the logfile /var/log/squidGuard/squidGuard.log from time to time...