Lets say we want to permit access to most every website on the Internet, but deny certain websites. Create a file named blocked_sites.

touch blocked.sites

Add the sites to be blocked to the blocked_sites file.

www.example.com

Add the following in /etc/squid/squid.conf or /etc/squid3/squid.conf:

acl blocked_sites dstdomain "/etc/squid/blocked.sites"
http_access deny blocked_sites

The ps command can be used to determine if your system is using init or systemd. If PID 1 is init, then you will use the service command. If PID 1 is systemd, then you will use the systemctl command.

If your system is using systemd, use the systemctl command to start and enable squid.

systemctl enable squid 
systemctl start squid 
systemctl status squid 

If your system is using init, use the chkconfig and service commands to start and enable squid.

chkconfig squid on
service squid start
service squid status

www.example.com should now produce the following:

Access can also be denied for certain keywords. Create a file named blocked_keywords.

touch blocked.keywords

Add the sites to be blocked to the blocked_sites file.

porn
pornography

acl blocked_keywords url_regex -i "/etc/squid/blocked.keywords"
http_access deny blocked_keywords

If your system is using systemd, use the systemctl command to start and enable squid.

systemctl enable squid 
systemctl start squid 
systemctl status squid 

If your system is using init, use the service command to start and enable squid.

service squid enable
service squid start
service squid status

Porn websites should now produce the following: